Restauration of RCA radio receiver model Radiola 26 Great, I won ebay auction for a 20's american radio set ! This is an earlier superhet, a first generation battery powered radio. I got some rare doc on the Web. The supposed schematics -supposed, because in reference with texts, it seems that to hide precious superhet circuitry, RCA had potted components in container- is like this: (schema.pdf) Funny: our american friends give then name "Catacomb" to this container.... Does the fact that this box is located under the tubes sockets plate, and is airtight, such as the "Catacombs", or because my poor english does not allow me to understand this term ? I think I'll be enjoyed to work on this set ! Six tubes are required for this set: UV199 type, 6 triodes with the same characteristics as WD11, except heating; so, I could make some replacement tubes... The UV199 embases are nearly the same as the 01A's of the AK20, so I could make replics. The tubes are not here, but this is no so bad: no risk to be broken during shipping. I got wiring diagram too, with continuity tests (proceeded from outside catacomb box) (cablage.pdf) Now, I'm waiting for monster arrival.... 1. The arrival. Great, the parcel has just arrived this afternoon! It is intact and it has taken 6 days: gone from Ohio on 18, arrived in Normandy on 24! It must be said that everything went well: no error, no falls, no lost.... Here are some pictures of the package, congratulations to Joe for the package! (PG_CL95) (PG_CL97) (PG_CL99) (PG_CM01) 2. Inventory. Beautiful, this set. When closed, it's a simple wooden box : who might think that this is a radio set? (PG_CM03) When opened, it is not more explicit ... We must still admit that these battery-powered radios look a bit strange! (PG_CM07) As I got some photos on the Web of a Radiola 26 in very good condition, I can look at mine, and make a list of what to do. A) the ebenistry has suffered an attack of moisture: the veneer falls off over a large area. Funny, in Europe, the battery radio-sets had plain wooden boxes, the veneer was used on mains-powered radio sets. (PG_CM13) Moreover, the door (loop antenna) fixation is weak and the whole ebenistry is not enough strongly assembled (corners in the brackets must be tired) (PG_CM12) B) handle is left (I noticed several photos it is rare to find the set with its handle), but the ties are there, and all the fittings too. (PG_CM05) C) the plate cover that hides the tubes is left too. (On other photos, I can see it) D) the 6 triodes are not here (UV99) E) when we shook the set, there are things that go around within F) Horn speaker (HS) is here, it remains to verify whether it's coil is good... (PG_CM11) G) obviously, no batteries, but all the wires seem to be there. (PG_CM08) H) the manufacturer's plate is there, serial No.: 214452. (PG_CM09) For the moment, I can't say that this is a ruin: the body is tired, it's true, but who is not tired when 83 years old? It remains to open the monster ... 3. Disassembly. I have not found any disassembly notice, then I shall note in the same time I shall do. I will take the opportunity to take some photos of disassembly. A) removal of the grid that hides the HS. Simply pull the top to yourself and to provide the 2 peaks at the bottom. The fact remains that a single elsewhere. (PG_CM14) B) removal of the door. First, unscrew the antenna control knob at the top of the frame to disengage the top of loop antenna box, then pull it. (PG_CM15) (PG_CM16) (PG_CM17) Then unscrew the hinges. On the bottom and intermediate hinges are the wires of loop antenna. After unscrewed, it is necessary to cut off the 2 wires that are welded on back side of hinges, in a hole in the wood. (PG_CM19) (PG_CM20) (PG_CM22) (PG_CM23) C) disconnection of the power supply plug (PG_CM29) (PG_CM30) (PG_CM31) D) removal of HS (Horn Speaker). Simply unscrew the 2 screws that hold it on box, through the battery compartment. (PG_CM32) The HS is also hold on a third block; you need pull to the right to disengage block. Then unscrew the 2 nuts that hold the 2 wires, on LS body. (PG_CM33) (PG_CM37) (PG_CM34) I take this opportunity to measure the coil: about 1900 ohm, is a good sign! (PG_CM35) These wires cross two times through the body, it is necessary to drag the wires when radio chassis removal. (PG_CM36) Here is the HS outside the body: (PG_CM40) E) displacement of the 2 wires of loop antenna. One wire is soldered on a plug at the bottom of the box (which makes contact with the bottom hook), in the battery compartment. You must unsolder it, then you can then drag it from the hinge into the battery compartment. (PG_CM41) (PG_CM44) (PG_CM45) The other wire (intermediary hinge) has a wire that goes to the top hook. These 2 hooks could be used to fix the loop antenna at the rear of the radio set, instead in the front door. To get there, you must remove the cardboard plate fixed by 4 small nails. (PG_CM48) (PG_CM50) (PG_CM51) (PG_CM52) (PG_CM53) When unsoldered, the wire is free and as it does not pass through the body, then you can remove the radio chassis. (PG_CM54) F) removal of the radio chassis. You must remove 4 screws at each corner (not the two medians). Then, you pull up the radio chassis accompanying wires and powered cord through central hole. (PG_CM46) (PG_CM47) Here are some pictures of the removed chassis. Seen from below: (PG_CM55) Retail local oscillator coils: (PG_CM57) One of variable capacitors: (PG_CM58) Elastic suspension: (PG_CM59) power decoupling cap.: (PG_CM60) Damper (red) and 2 capacitors: (PG_CM61) Box "catacomb" (PG_CM62) Seen from top: (PG_CM64) from front: (PG_CM65) disassembly check up: Ultimately, it's easy to disassemble. Moreover, when removed from the body, the radio chassis is easily testable: everything is available (except, of course inside the catacomb!), and the whole may be tested as it is. I found that the 2 red dampers of the catacomb have fully cured and that the 3 dampers holding HS also died. The coil of HS seems good (at least its resistance ...) By knocking on the walls of the catacomb I realized that they resonate as if the box was empty. Will I lucky that tar is potted only at the bottom? When empty, the ebenistry seems easy to restore, after all, only the veneer, then with plasticine and wood veneer sheets, I should get out. At first glance, this radio chassis is slightly different from the schematics that I have: I have not seen jack for external loudspeaker nor 5 / 6 tubes switch. In addition, there are 2 plugs on the front panel of which I know nothing about the use (for the moment ...) We can, by removing loop antenna form the door, to operate the radio set with an antenna that hooks to the rear. The local oscillator coils do not seem to have suffered. The decoupling capacitor on +90 B has inflated a bit. It looks funny, it is visible from the outside. 4. Check the real wiring, new schematics. A quick review of wiring to realise that indeed, there are some differences: (schema7.pdf) As there is no switch to select 5 / 6 tubes, the T11 transformer is in operation at all times, therefore connected to the anode of L5. Similarly, there is no jack for external LS, the HS is therefore permanently connected to the anode of L6. The 2 plugs are in parallel with the primary T11 (H1 and H2), we can connect the headphones. A capacitor filtering AF is connected between the anode of L5 and the ground (CU) There is no antenna plug, nor coupling cap., however, the two rear hooks(A1 and A2) permit to install loop antenna. For the rest, everything looks the same (except that I did not open the catacomb!) 5. Opening catacomb. I just realized that the walls of the hollow sound box, in other words, do not seem to adhere to the potting inside. So I will try to open this box ... Rather, I will try to get the whole container. It seems to me regularly, and if really it retracted his potting, I should be able to succeed. So I started with the catacomb uncoupled from the rest. First, we need to dismantle the 2 lateral suspension 2 forming half circles. (PG_CM87) (PG_CM89) (PG_CM90) Then there's unplug all cables arriving in the terminal's catacomb. Although I have the wiring diagram, the reassembly will be facilitated. I use small pieces of tape of different colors to keep marks, and I made a good amount of pictures from different angles. Here are few of them: (PG_CM93) (PG_CM94) Some cables are retained by strings that must be cut. (PG_CM95) (PG_CN03) The power cord can be folded to the front (in fact, there is a wire connected to the variable resistor "K" that I have not yet removed ... I will do during front plate restoration) (PG_CN04) It should also disconnect ground wires as well as those which are connected to the 2 caps. (PG_CN05) (PG_CN06) (PG_CN08) Joining anode L5 includes 4-wire soldered together (anode-primary T11-CU-H1) must be cut the wire that goes to the front plug (PG_CN09) (PG_CN10) The catacomb began to emerge, but there is a common thread that we must unsoldered (it connects the 2 µF capacitor "BC") (PG_CN11) (PG_CN12) This is the catacomb released (PG_CN13) Clearly the number of this unit: C 206443. (PG_CN14) To access the inside, remove the top sheet (PG_CN15) (PG_CN16) And here's the monster wiring. The 6 tubes sockets form a single plate on which everything is riveted or soldered. (PG_CN17) To extract the circuit, I tried with a screwdriver to lever (PG_CN18) And it works: by turns at each end, the entire circuit slides out of the box. (PG_CN19) At one point, all frees itself: here is finally unveiled inside! (PG_CN20) Only the coils and the 5 Meg resistance were drowned, the capacitors are apparent (so are replaceable ...) and it's not tar, but only paraffin! 6. Verification of catacomb Of course, at this stage, it is hoped that the drowned components are in good condition. It is hard to imagine how to change one of the coils. Of course the internal wiring informs the whereabouts of the coils, but we must melt the paraffin in the right place but could perhaps unwind the coils if they are impregnated. The least I can do is to test the coils by measuring the resistance at accesibles points. If I can think a little bit, and with the wiring and principle schemes I can access at all! Indeed, the fact that capacitors are not drowned, some connections become accesible. Below are the results of measurements of resistance: T11 (BF transformer No. 2): P = 1100 ohms, S = 5900 ohms T10 (BF transformer No. 1): P = 1100 ohms, S = 6000 ohms R: 5.1 Mohms T5 (FI transformer No. 3): P (S6) = 52 ohms, S (S9) = 195 ohms T4 (FI transformer No. 2): P (S8) = 33 ohms, S (S4) = 156 ohms T3 (FI transformer No. 1): P (S5) = 33 ohms, S (S3) = 60 ohms, N (S7) = 54 ohms T1 (modulation transformer): P (S2) = 10 ohms, S (S1) = 13 ohms Whew! As we can see, everything is good. Incredible, after 83 years, all the components are intact. It would seem that everything has kept drown. I can only check capacitors. That is less easy, I must unsolder one wire of each cap. to be able to do test. Here's where these capacitors. C1, C5, CN, C3 and C6 are on the side of L1: (PG_CN33) At the lower end, C3 and C6 are on each other: (PG_CN37) C2 and C4 in the middle of the circuit: (PG_CN35) Given the pattern, it is that we can verify the capacitors C2 and C4 without unsolder them: C2 = about 150pF (instead of 250 pF); this capacity is not very critical C4 = about 170pF (instead of 50pF) is the detection cap, it would be great to change it ... For the other caps, I am compelled to isolate for measuring (they are all in parallel with coils (except for CN that I could measure unedited) I unsolder one of the legs of C1, and there, disaster: the connection opens in the paraffin! In other words, I have no means to rebuild without the melt it to a depth of at least 1cm. Ouch, big mistake! 7. tentative for melting the paraffin. I shall try to melt the paraffin at least on the right side, ie under the caps C1 .... C6. Here is the method: I put the catacomb on 2 tin box under which I put another tin plate. (PG_CN42) The catacomb is placed in the right direction, paraffin down, therefore. Then, with an heating tool, I melted paraffin to discover the connections on C1 (there are 2: S2 coil and coil S8) We must move on the heating , not to remain in place under pain of the burning paraffin (and it really smells bad) (PG_CN44) 8. Repairing and continuing verifications The 2 wires emerged, we must bring them together with a small piece of multistrand to make a good soldering. (PG_CN45) A) Until C1 is unsoldered I measure it: 1200 pF (instead of 200 pF), no hesitation, I must change it. Before doing so, I get to check C5. To isolate it, I do not unsolder anything: I cut the connection at the +90B connector. (PG_CN46) B) Measure C5: 1100 pF .... strange ... and if normal values were they? C) I will check the resonant frequency. For this, I reconnect C1 reconnects with the small wire. And I do the test as follows: (Schema8.pdf) I connect a sinus generator between the grid connection of L3 and L3 the -C plug. The oscilloscope connected to C1, is ground on +90 B, hot point on the redone soldering. And I do vary the frequency of the generator around 42kHz, nominal value of the IF. Result: The resonance is located at 42.6 kHz, in other words, C1 is good, and the nominal value is 1200 pF (and not 200 pF!) I take to measure the -3dB bandwidth : Fcb = 40.8 and Fch = 44.4 kHz, so, the band is 3.6 kHz ... receiving HiFi is quiet impossible !.... D) I checked in the same way the other IF transformer, as the wiring follows: (Schema9.pdf) Result: The resonance is located at 42.9 kHz. So C5 is good too (a little weak) and the 300 Hz gap between the 2 resonances does not require resolve C5. Whew, I know now that the 2 FI transformers are good and not too bad tuned. E) Measurement of C6 (50pF): This capacitor has a insulated connection (loop antenna input),so measurement is possible. I measured 150pF. Value a little big ... but acceptable. Besides, is 50pF the good value? Measure C3 (50pF): the best is unsolder the triple point C3-CN-S7 because it is also necessary to measure CN. Results: C3 = 150pF, CN = <5pF. F)we can now summarize the results: (pF values, and in brackets values figuring in the diagram) C2 = 150 (250) C4 = 170 (50) C1 = 1200 (200) C5 = 1200 (200) C6 = 150 (50) C3 = 150 (50) CN = <5 (not measurable) In view of the error on C1 and C5, I would prefer to say that the values on the scheme are wrong and that measurements are good. C2 is anyway not critical C4: its real value measured seems more coherent than 50 pF, the RC4 time constant is 0.85 ms, so a cut-off frequency of 200Hz, which is quite proper for a grid detection. C1 and C5 must have the value of 1200 pF for the IF : 42kHz. C6, antenna input, may well have the value of 150pF instead of 50pF, it is not critical because the impedance leak grid L1 is a coil (S3), which must have an important value for broadcasting range. Only the ideal value of C3 is difficult to determine: it depends on the self S7 and the neutrodyn compensation cap CN whose value is also unknown. CN seems to have a correct value. After all, it's not very inconvenient, the UV199 ersatz will present a grid-plate capacity certainly much less than the original tubes, neutrodyn compensation be justified unless ... In short, I believe the catacomb is functional ! I must put the box on, now. The operation is very simple, simply drag the block in the box and put the screws (6, 2 longer in the middle) 9. Following checks. A) measuring CT (is the cap, which remained hung catacomb, it comes in parallel on the HS): about 2nF. The leakage resistance gives more than 30Mohm. So CT is ok. B) CU (the cap which is set alongside CT on the front, in parallel with the primary T11): 2nF too, leakage resistance > 30Mohm also ok for CU C) CB (the cap filtering +90B): the leakage resistance gives 18kohms, the capacity is about 1 µF. In other words, CB must be changed. D) measuring variable capacitors: 660pF maximum. No short-circuit during operation. OK. E) measuring rheostats: K = 5 ohms, U = 50 ohms. These values seem quite correct. F) measuring local oscillator transformer: 2 windings (each is 2 coils in series) are 1.5 ohm each. OK. On the front side, CVs and rheostats operation is hard: I must dismantle all these components for cleaning and lubrication. 10. Rehabilitation of the front panel. To carry out this repair, we must lay down their components attached on the front panel. First, the var-caps. we unscrew the screw locking pinion gear on the command axis: (PG_CN51) The button and the axis can then exit through the front panel. (PG_CN52) It is necessary to remove the pinion (PG_CN53) We do in the same way with each rheostat axis. (PG_CN55) If the axes are seized, it is necessary to use unseizing agent to prevent breaking the button. If we must use pliers, it is necessary to interpose thick fabric: (PG_CN57) The needles dials varcaps are to be removed; for this, we must remove the nut-eyed: (PG_CN58) These needles appear to come from an old clock: (PG_CN59) When the 4 axes are off, it remains 2 large screws, between rheostats, that hold the wooden plate; they must be unscrewed. The plate is then released (PG_CN60) And then we discover varcaps and rheostats fittings : just unscrew the 3 screw of each varcap for deposit. (PG_CN61) Then the 2 bolts of rheostats. The two variable capacitors released: (PG_CN62) The rehabilitation involves polishing the steel wool axes, and to lubricate them. The sliders of rheostats will also be polished, as well as the center contact on the axis. For the varcaps, needless to desassemble them: it is necessary to lubricate the axes and operate them by hand until they rotate freely. The front wheel covers, as well as the varcaps needles, screws and sliders of rheostats are pickled in the diluted acid, and then scoured; Finally, they are polished with steel wool. Incoming state: (PG_CN63) State after cleaning: (PG_CN65) The wood can be cleaned (steel wool) and varnished or waxed. The oscillator coils plate must be deposited for removing dust and checking it. (PG_CN66) Each coil resistance is about 1.5 ohm (in fact, there are 4 coils, 2 by 2 assembled) We must also inspect rheostats: they are crossed by significant currents and the slightest bad contact would be detrimental to the proper functioning of the radio. (PG_CN67) It is best to deposite them from the front plate, but if everything appears normal, we can be content to use very thin sandpaper on the turning contact (the central puck) and on the track (resistor winding thickness) For me, the rheostat "K" (the one that compensates the reduction of heating-battery voltage during discharge) is out: Indeed, when I have tried to unsolder the last wire of power cord, I found that riveting was broken! (PG_CN70) This was hardly visible before oscillator coils deposit, if I had not done so, I would not have had heating ... I made this riveting by using a 3 mm(diameter) bolt. The best thing is to tear down the winding of the basement. (PG_CN71) The screw is a little grinded so, it does not exceed. (PG_CN73) (PG_CN74) Just to fix the rheostat on the front panel. The capacitor CB needs to be changed. Its value is 2µF. Initially, it is not polarized, but we can use an polarized one. A voltage of 160V is sufficient. I prefer to use 2 caps 1 µF/250V not polarized ... When the capacitor is removed, it must be emptied. (PG_CN76) (PG_CN78) Not many methods: the drill with a 10 mm drill. We make several holes and with pliers, we remove chips. It is long, tedious and dirty. When the box is empty, we install the new capacitor with 2 wires. (PG_CN79) And we all drown (I used paraffin recovered from the catacomb) (PG_CN80) Simply connect the 2 wires to the terminal (PG_CN81) And fix the cap on the front panel. Well, the front panel is revised; reassembly can begin! 11. Reassembly We need to start fixing the dials on the wooden plate: (PG_CN82) I changed the 8 screws that were really oxidized. Instead of spending time to renovate them, I have prefered using new brass screws. They are a little longer, I had to grind them when being in place, just at the edge of the nuts. Then the wood front plate is attached to the metal frame with 4 rounded heads screws: (PG_CN86) Then, the axes is reinstalled the varcaps needles too. Do not forget the rheostats needs that are washers wich have to be put under the buttons. (PG_CN87) The catacomb shock absorbers were completely dry: (PG_CN89) (PG_CN90) I have decided to rebuild new ones. Here is how I have done: A) I first cut 2 shapes in cardboard to make boxes whose dimensions are 44x28x26 (PG_CN91) And 2 internal walls approximately 25x21 dimensions. B) when boxes are assembled, partitions are glued to mid-length, on the bottom. (PG_CN92) C) I cast silicone rubber that I dyed red. D) then, we can unmould: (PG_CN93) (PG_CN94) E) the wall remains in rubber, but it is easy to remove it: (PG_CN95) Below are the new blocks installed in their place: (PG_CN96) (PG_CN97) The slot is closed, it is normal, I expected slightly lower dimensions for all to be held. These are the legs of catacomb that will come into these slots. The catacomb is fixed with 2 semicircles. Initially, these pieces were each in a different direction, but during reassembly, I preferred to put all of them oriented in the same direction: (PG_CN98) 12. chassis rewiring Now I can rewire the catacomb. The colored marks posed during dismantling are very useful ... When the connections are screwed, the power cord must be shrinked, as well as the 2-wire link to CB cap: (PG_CP01) (PG_CP02) Here are some pictures of the revised chassis. View from below: (PG_CP04) To the right: (PG_CP05) To the left: (PG_CP06) Seen from above: (PG_CP07) other views: (PG_CP08) (PG_CP09) Front view: (PG_CP10) 13. Manufacturing electronic tubes replacements. Initially, the tubes are UV199, universal triodes with low transconductance (0.425 mA / V) and medium plate resistance average (15.5 kohm). Their embase is "small 4-nub", about 25 mm diameter, with 4 identical nubs, positionned in accordance of the peaks of a about 12mm side square peaks. The dimensions are not critical because the contacts are made on the termination of the nubs, on slats fairly broad. The locking is done by one bayonet. The embase height is about 20mm, while the original tube had a total height about 88 mm (including nubs). The most critical point is to rebuild the bases. Here's how to do. >From a died capacitor 25 mm diameter, it is necessary to make a matrix. On this matrix, I stuck 4 plots on its face and a fifth one for the bayonet, which is 4 mm long, while 4 others are 5 mm long. The bayonet axis is just between 2 plots, and at a distance from the tip of the plots of 15 mm. (PG_CP11) Just take a mould of this matrix with silicone rubber. In a tube internal diameter of 18 mm, rubber is poured, it will be the inner cylinder mould. (PG_CN21) This must be split along 4 generating lines, 90 degrees shifted , to a depth of 2 to 3 mm no more. To pour the base, we must prepare: -- A small piece of 3 mm threaded rod with a 10 mm length, that is inserted into the hole of the bayonet (PG_CN38) -- 4 flexible insulated wires (different colors) soldered on four 3mm diam. screws 3mm, 14 mm length. These wires are inserted into the slots of the cylinder, the four screws are positioned in the end. These are introduced into the 4 holes of the mould. Ensure good orientation of the four wires depending on their color (red = anode, green = grid, black = minus heating, blue = plus heating) (PG_CN39) A notch in the end of the cylinder allows the passage of the screw of the bayonet. When black colored resin is poured, harding takes place within a few hours. (PG_CN41) We must then verify that the base fit well in a catacomb of media, and is well maintained. (PG_CN47) If it does not fit, you can try sanding lightly the resin. If it does not locked, is that its diameter is too small, we must redo the mold. In this case, we stick on the matrix few rounds of tape to increase the diameter and redo operations (except the inner cylinder) If the lock is difficult, it is necessary to grind slightly bayonet and nubs ends. Normally, after a few tests, we get good bases that fit well and lock perfectly. (PG_CN49) (PG_CN50) To achieve the "ersatz 99", I decided to use 3Q5s. These batteries pentodes really look nice. (PG_CP21) But first I have to make sure that I can use them with roughly the same characteristics as 99. I made a quick installation for measuring the anode current by varying the voltage anode 90 to 100V and voltage grid -4.5 to -3.5 V. I wired the 3Q5 in pseudo-triode mode (180kohm resistor between G2 and A) Similarly, a 270 ohm resistor is wired in parallel with the filament to obtain a current about 60 mA for heating. The obtained lamp is heated with 2.8 V (instead of 3V for 99) but it is not inconvenient, because there is a rheostat for tuning voltage battery. Here are the results: A) Vp = 90V Vg =- 4.5 V Ip = 2.4 mA B) Vp = 100V Vg =- 4.5 V Ip = 3mA C) Vp = 90V Vg =- 3.5 V Ip = 2.9 mA from a) and b) we get: Rint = 16.7 kohm (internal res.) and from a) and c) we get: s = 0.5 mA / V (transcond.) What's really close to a 99! (Rint = 15.5 kohm, s = 0.425 mA / V for Ip = 2.5 mA) I even made a measure in detection mode: D) Vp = 45V Vg = 0V Ip = 1.8 mA When these measurements are made, I can begin to make the first substitute (ersatz) "99-A". It is necessary to remove the base of the 3Q5; for this, it is best to cut the pins, then turn the base to break the glue. (PG_CP22) (PG_CP23) Here is a small outline to notice wires emerging from the base of the bulb (PG_CP24) When the rests of glue are removed, we cut the wires near the base of the bulb, except wire of G3 which can be cut very small, because not used. Then the 270 ohm resistor has to be solderer on the 2 wires of the filament, the 180kohm is soldered between anode and grid 2. (PG_CP12) The 4 wires of the base are cut, keeping approximately 5 mm length above the upper side of the base and connected to the lamp. (PG_CP13) Then we glue using thermogun. (PG_CP16) This is the first rebuild 99: (PG_CP17) plugged on the Catacomb: (PG_CP19) The lamp height is about 80mm; here is, seen from the front of the radio set: (PG_CP20) 14. Testing the first ersatz: LO verification. As I have made only one substitute, I decided to test it in the local oscillator stage. The operation is easy: plug in the power supplies, and a oscilloscope on the oscillator coils. However, it should be noted an important point: as the test is done with only one lamp, you either limit the heating voltage ( "A"), either limit the current with a 22 ohm resistor in the circuit. Without this precaution, there is a risk of burning the filament of the lamp! Here's how to connect the power supplies (no need to connect the +45 V): (PG_CP25) The oscilloscope can be connected to pin #5 of Catacomb: (PG_CP26) The lamp is plugged in slot #2: (PG_CP27) Here waveform when the varcap is maxi: (PG_CP28) The frequency is 239kHz .... very strange ... On the other hand, when the varcap is mini, the oscillation does not occur; If we want the OL works well, varcap tuning must be at least 10%, in this case, the maximum frequency is 543kHz. Is there any problem? 15. Wiring another ersatz. During ersatz tests on RCA radiola III, I tried a 1L4 with success... Maybe this lamp works too? Wire it in triode mode (G2 = A) and adjust the heating voltage (1.4 V) I decided to quickly wire an adapter, which is to say that I use a 7-pins miniature socket wired with a 4-nubs base, in this way, the lamp becomes replaceable. Here the lamp, ready to be tested: (PG_CP29) 16. Testing this second lamp on the LO stage. The results are identical: same frequencies. Just a small difference: this lamp does not allow -10V for -C bias, it requires minimum -7V. Otherwise, the oscillation does not start ever. So, this proves that whatever the lamp, the oscillation occurs at really low frequencies . Pondering a little, could we not imagine that the use of second harmonic of the LO produces the beat? Consider the numbers: varcap mini: Fmax = 587kHz (with the 1L4) multiplied by 2 = 1174 kHz varcap maxi: Fmin = 239kHz multiplied by 2 = 478kHz Assuming that we take the lower beating, it means that the wavelengths that can be received will be fixed between: 300000 / (1174 +42) equals 247 and 300000 / (478 +42) equals 577 meters. Values that I think are quite acceptable. To make sure it is the #2 harmonic which is used, I can measure the inductance of the coils of the local oscillator ... To do this, simply unplug the 3 wires of the coils from the Catacomb, and the wire on the varcap too. Then input a signal on the non-tuned coils, and visualize the signal on the other coils, tuned with fixed known value capacitor, then tuned with 2 identical caps (or one with double value). Thus, through this little spreadsheet file, with 2 measures, I can determine inductance and capacitance of the coil. (Osc-radiola-26.xls) The inductance is approximately 550 µH. The capacitance is around 30pF, that gives, with varcap tunde on max, a frequency about 250kHz, which is consistent with what I found. Thus, by design, it is truly the second harmonic beating with the incident wave to produce the 42kHz IF. 17. Constructing other substitutes I tried several other lamps tu substitute 99. First, a 3S4 that has not yielded good results in LO stage, then a russian 2SH27L which gives good results. I made a 2° ersatz of the first type (with a 3Q5), and then, surprise: no more oscillation! I had to remove the 180k resistor, i.e. wire it in truly triode mode. Then I get a 5° version that works well. Summarize: "99-A" based on 3Q5, worse than version -E "99-B" based on 1L4 "99-D" based on 2SH27L "99-E" based on 3Q5, best version. ("99-C" is abandoned) So I built a total of 6 ersatz: one -A two -B two -D one -E Here is a picture of the lamps set: (PG_CP31) And the outlines of the 3 versions that I keep now: (Ersatz-99.pdf) 18. Measuring and cleaning the loop antenna. The loop antenna is hidden in a cut corners square box. (PG_CP32) Removing the 16 screws of the cover plate, we discover the winding: 20 turns, which average area is about 480 sq. cm. (75 sq.inch) (PG_CP33) ******************************************* It is also noteworthy that there are 3 contacts: -- one at the top : the end of winding, which is linked to higher peak. -- one at the bottom, on the axis: the beginning of the coil, connected to the lower peak. -- another at the bottom, connected to 2 pins: a tap at 1.5 turns from the end of the coil. Only 2 contacts are used, connected at the hinges of the door. (PG_CP34) The 2 peaks are used to hang the antenna to the rear of cabinet (notches A1 and A2). In this case, the entire winding is used, but when the loop installed in the door, across the hinges winding used includes 1 lap and a half less (probably to compensate the length of the wires?) The central contact, bowl-shaped, touches the central plot of the door which is connected to the lower hinge; The 2 peaked contacts touch the circular contact of the door connected to the hinge between. No contacts through the hinge higher. It should be scrupulously check these contacts, in particular the wires are practiced in grooves in the wood of the door, hidden by wax. The hinges themselves include spring of threads that connect electrically the 2 parts that are moving one to the other. The measure of the inductor of the loop antenna gave 115 µH, the capacity approximately 40 pF. With the varcap at 660pF maxi, this will give a minimum frequency about 560kHz, i.e. a wavelength about 535 meters. (Part-radiola-26.xls) All the metallic components of the loop and the door must be removed and cleaned (acid, polish, steel wool ...) (PG_CP36) I took the opportunity to redo the contacts of the hinges. Simply put unsolder-braid around the axis and solder each end on each part of the hinge. We must do a turn and a half of braid, and does it in the open position of the hinge. Thus, when it closes, the braid is a little longer, but does not block the closure. (PG_CP37) (PG_CP38) I took the opportunity also to redo the notch lock of the door: a screw was missing, and the use was such that the remaining screw was not fixed. On the other hand, we see clearly that the 2 screws crossed the wood. So I rebuild 2 screws (by cutting 2 new screws at suitable length), and I put the plate on a thickness of wood cement, so it is better hanged. (PG_CP48) This wood cement must be tinted to be invisible. Then I glued a small piece of veneer on the box (wood glue) Just then sanding the wooden parts and eventually ending with steel wool; a layer of satin varnish will finish the antenna and door restoring. When the varnish is dry, metal parts must be reassemblied, especially the hinges that must be soldered with wires links (below). (PG_CP46) (PG_CP47) 19. Horn speaker. During the removal, I was able to measure its resistance about 2000 ohms and I had concluded that it was ok. So I wanted to check it with the help of a generator, and then, surprise: nothing ! By measuring its resistance again, I find infinity value! And the cause is there, obvious: at the release of connections, I had to force, and one of the 2 bolts runs free, in other words, I cut the internal wire connection! I have to disassembly the motor ... First I removed the 2 shocks, which are in fact made up of 2 rubber discs each, and a big washer is sandwiched and connected to the body of HS with a rod. (PG_CP41) (PG_CP42) (PG_CP43) The third shock has no washer, the rod welded on the ear that comes through one of the rubber discs. The discs are about 6 mm thick with a diameter of 38 mm. (1"1/2) The best thing is to do new discs in silicone rubber. The motor is screwed on the ear, 2 fiber seals are interposed. (PG_CP39) To disassemble the motor, I see only one solution: unscrew the body which is made up of 2 parts. Unfortunately, the first attempt was unsuccessful: seizure! So I leave the junction of 2 parts in the dégrippant some time ... So I tried again using a key filter: (PG_CP45) Nothing to do! I have forced with this key, the motor caught in a vise, everything is blocked. So I tried to screw 2 bolts, in order, with a metal bar, to make a kind of key: (PG_CP49) And this is the result: the aluminium smelter did not resist! (PG_CP50) So I decided to open ... For this, I use a diamond disc on a mini-drill: (PG_CP51) As I do not know how are disposed internal organs, I go in a haphazard manner; I cut arcs: (PG_CP52) (PG_CP53) Always hoping to be able to run the whole, but there is nothing! I go on ... And ultimately, I reach the wiring connections of the coils: (PG_CP55) Thinking bad contacts are located on the 2 pods, I decided to solder 2 brass screws. And in fact, doing this, I get the 2000 ohm again, whew! The reassembly is quite simple: I glue the pieces with cyanoacrylate glue. (PG_CP58) And I filled sawing straits with automobile mastic. I checked the resistance: horror, I always have bad contact! Unbelievable .... I desassemble again, but only on the screws side: (PG_CP59) I saw another piece to discover the other side of the pods: (PG_CP60) And there, I can see that the contact is made with a soldering rivet. We should not look any further, the bad contact is here! I solder the 2 rivets, the contact is restored. I reassemble all pieces. Here is the motor repaired: (PG_CP61) I measure the resistance one more time: ok. Two hours later, I measure the resistance: cut again! groar ! I do not understand anything. Or the problem is simply one of the coils to be intermittently cut ... I make this test: I tune a power supply for 100V and I put contact on the coil. By doing so, I hope to provoke a small electrical sparkle at the wrong contact and perhaps a mini welding will be made ... And it works: The contact is restored ! I will still monitor the motor of this horn speaker: I now know that it may cause me trouble. In any case, this is not the fact of having unscrew the 2 wires that caused this bad contact, I think it was inevitable. Well, if the problem recurs, it will be necessary that I decided to completely dismantle the motor to gain access to the coils, to be repaired. So, to be continued ... 20. Shock absorbers. The easiest way to rebuild them is to use the original bowls as metal moulds. They must be obtured and we have to pour silicone rubber. (PG_CP62) (PG_CP63) We get 3 double thickness slices ,it is enough to cut through the thickness to obtain the 6 washers. (PG_CP77) (PG_CP78) We must make holes in 3 of them for the passage of axes. The reassembly is simple: we put the holder, the holed slice, the big metal washer that is screwed on the axis. (PG_CP79) Then screw the holder on the stand after the another rubber washer was interposed: (PG_CP81) This is the HS fitted with its 2 rear shock absorbers, ready to be screwed in the cabinet. (PG_CP82) The third shock fits directly on the wood. 21. Cabinet. The cabinet of this set is plywood made. It suffered from moisture, the veneer comes off on the top and on the high sides. The rest is in a much better condition, just a little off, but no more. To redo the cabinet, remove everything: Handle anchors (PG_CP64) And the inside reinforcement wich is attached to the sides (PG_CP65) Tapped legs for fixing chassis (PG_CP66) Contacts rear antenna (A1 and A2) (PG_CP67) The lock of the rear door (PG_CP68) And the batteries support and connector. Here is the naked cabinet, ready to be renovated: View from the front (at the top :radio chassis compartment , at the bottom: horn speaker compartment) (PG_CP69) The right side (PG_CP70) The rear (battery compartment) (PG_CP71) The left side (PG_CP72) The underside (I left foot metal) (PG_CP73) And the top (PG_CP74) A) Repairing the top of the cabinet The top veneer can already be removed completely, it does virtually over. (PG_CP75) Discovered on the 2° layer of veneer with some material lacks. (PG_CP76) The first step is to paste the remaining pieces on the intermediate layer. Pliers and weights maintain pieces under pressure during glue harding: (PG_CQ19) Then fill the lacks by sticking cardboard 1 mm thick. Just cut out the shapes of the lacks keeping few millimeters joints. (PG_CQ21) A stroke of plane may be necessary to remove the lumps: (PG_CQ23) When the wood glue is dry (about a half of hour), we can use mastic to fill the interstices of pulp wood. (PG_CQ24) It must be very dry to be able to sand. (PG_CQ26) Thus, the surface is sufficiently corrected in order to receive the veneer. (PG_CQ28) I used thermofusible veneer. We must cut a piece slightly larger than the top (1 or 2 cm more) Then it must be positioned in such a way that a good side is on the front. (PG_CQ48) Normally, this veneer sticks with an iron, but the heat fan is more speedy! (PG_CQ49) First, paste a side, and then moves on the heater to the other side. I press with the hand with a rag to the heated place. When everything is stuck, it is necessary to cut the overruns with cutter on the reverse side of the veneer,laying it on a hard surface. This is what we obtain: (PG_CQ50) View from the corner: (PG_CQ51) Then we have to cut the 2 circles for the passage of the handle. First, I spotted the axes: they were strictly on the median in length and at 94 mm from the edge. 2 small crosses indicate centres (PG_CQ53) Cutter is used, from the center to meet the board. You must make sure that the support fits well (PG_CQ54) Those are the 2 cuts made: (PG_CQ57) The next day, it shall be ensured that the veneer is no bubble. Indeed, after a cooling time, it does happen. It is sufficient then to heat again locally and highly press. During one day, we have to check several times and it was only after 48 hours that is safe for work. It is better to lose a little time at this level, than be forced to heat again once varnish is applied! B) Repairaing the sides The sides are damaged on the top: (PG_CQ31) The veneer is off, but all can be kept. (PG_CQ32) It is therefore necessary to make pieces of veneer to fill in the lacks. Just take the form by putting a sheet of paper on the lack and coloring with a pencil: (PG_CQ34) Then, with a cutter, you mark the veneer using the form on paper. The veneer is cut with scissors, and properly adjusted to fit the lack (PG_CQ35) When the form is good, it can be glued. (PG_CQ37) There are still some lacks that need to be filled with the pulp wood (PG_CQ46) Once the sanding done, we ca see the connections parts, but really a little. (PG_CQ47) C) repairing the rest of the cabinet. The rest is not too damaged. There are a few places where the veneer comes off a little. Some pieces of wood should also be replaced (tassels, partition ...) The pasting is done with wood glue, the press is improvised, it is good to keep transformers ... (PG_CQ38) (PG_CQ39) The corners are also off. For glue them, clamps are needed (PG_CQ40) The partition is reglued also, just put transformers for pressing: (PG_CQ42) The rear door is not too damaged, just a few scratches. (PG_CQ66) Its internal side is just dirty, it needs to use lightly steel wool. Be careful not to break the label metal nor glued one. (PG_CQ68) The renovation is to lightly sanding the outside, insisting on scratches to attenuate them. Two layers of varnish is enough: the first is wild cherry, the second is medium oak. The grid of HS is a little more damaged: one corner is broken and twisted. (PG_CQ70) In addition, the canvas is ripped at 2 places, including a very visible one. It is also very dirty. (PG_CQ69) The plywood plate must be re-adjusted and re-glued. For this, it is necessary to dry the glue under pressure, against a metal plate. (PG_CQ72) The canvas should be depasted from the board. It goes easily, but we must still be careful not to rip more. (PG_CQ71) Once washed, it must dry flat on a sheet of paper. Unfortunately, in general, when washing this type of canvas, it shrinks, and then, the piece is 2 cm shorter! So, it would be better to change the canvas. The original canvas is unprinted, but we can try to use canvases with drawings, or with different colours: (PG_CQ80) And the result can be pretty... Anyway, it's really a detail you can always change later. Simply paste the canvas at the back of the grid, only on the edges(like this, it may be easier to remove it!) D) finish When the veneering and filling are finished, we must now varnish. First we must sand the entire surface with fine sandpaper, then with steel wool. The first layer of varnish, wild cherry tint, is applied with brush. The drying time between layers is to be met. Here is the cabinet, front viewed: (PG_CQ59) Remember varnishing 1 cm back inside, because the chassis and the grid of HS are set back from the edge. (PG_CQ60) Tint is not quite the same as the original, there's the antenna door positioned near the cabinet for comparison: (PG_CQ63) However, the tints are close: (PG_CQ64) A second layer of the same color will surely darken. It must be sanded again with steel wool before applying the second layer. Finally, a third layer, medium oak, will get almost the same tint as the original. 22. First tests. A) These tests were performed while the cabinet had not yet been renovated. However, we can test the radio, without the cabinet. I used a mains power supply, the door with the antenna and the HS. Here is the whole of the installation of test: (PG_CP84) Lamps have been plugged in the following manner: (PG_CP88) Power supply has been connected on the connector with clips: (PG_CP89) (-C is set to -7V, +45 is connected to +40 V, heating is -4V) The loop antenna has been connected to the inputs of radio with crocodile clips. (PG_CP90) And the HS is connected to the 2 wires outputs (note the direction!) (PG_CP91) And here are the results: it does work well! The operation is very instable: the settings are difficult, scratching, wheezing ... I also tried to swap lamps, to see what happened, and, in general, it's worse, except for a few combinations: - You can swap the IF and the Detector (-B and -D) - You can swap the RF and AF # 1 (-A and -D) - You can swap the IF and the AF # 1, with a stronger level (-A and -D) - We can swap LO and AF # 1, settling -C at -5V (-A and -B) The optimum setting is: - Battery = 1 - Volume = 4 to 6 (except for the last 2 permutations: 1 to 2) - "France-Bleu" (864kHz): Selector 1 = 25 to 30, Selector 2 = 30. We can untune the Selector 1 to decrease volume; at perfect tuning, unfortunately, there is reaction (too much gain or regenerative operation between the coils of the LO and the antenna?) Conclusion: first test is good, I am going to build some another lampes to see if I can improve performances. It is also possible that the reactions were due to the characteristics of the lamps, higher than original ones. B) Now that the operation is validated, I can do some checking ... Firstly, given the low value of the IF (42kHz) the frequency image is not far on the dial, in other words, we must be able to receive France Bleu, for 2 different settings o Selector 2. Indeed, the 2° setting is for Selector 2 = 24. By adjusting Selector 2 to 27, we tune on the incident frequency, in other words, there is a violent reaction with antenna! C) adjustment, to improve the sound quality. By adjusting the following manner: -Selector 1 = 25 (instead of 30) -Selector 2 = 30 -Battery = 1.5 -Volume = 6 This gives a sound not so bad. D) intensities. The measures were: - IA (heating) = 0.23 A - IB45 (detection) = 1.3 mA - IB90 (+90 General) = 12.5 mA E) testing the 5 lamps mode. I removed the AF # 2, and putting in place of the AF # 1 (-E). The HS is connected to the sockets on the front panel. The result is not very good: clashes, level really too low. I get the impression that because the rheostat "Battery" is set at minimum, its resistance in series with all filaments (5 ohm) helps the reaction to occur ... 23. Continuing tests. Pondering a little, I thought that the problems of reception perhaps due to the fact that the ersatz lamps should have too much gain. So I tried to replace the lamps ... I had already done during the first test, but you never know ... For example, why is the best reception corresponds to rheostat "battery" setting at the minimum? I.e. for a heating voltage very low (about 2.2 V)? So I plugged the lamp 99-A in LO slot again, test which gave nothing. By turning clockwise the rheostats, the reception emerged, but very bad (reaction). And there's the chance intervenes: whereas until now, every time I swapped lamps, I put the power supply off, this time, I did not do it! I removed the AF # 1 for changing it and then, surprise: Lamp is absent, but I heat receiving, low, but clear, with no reaction ! In other words, the gain is so high that even with the AF#1 lamp is absent, the signal can pass (capacity leakage or induction leakage between 2 AF transformers ?). So I decided to look at the signals on the lamps grids. Here's what I seen (on 864kHz receipt, on day, loop antenna in the basement, Battery = 3, Volume = 5) The lamps were: 99-D 99-A 99-D 99-D 99-D 99-E (except that for each measure corresponding lamp is removed) A) grid of the IF # 2 (PG_CP95) We have already 600mV peak after the reflex-mixer stage! B) detector grid (PG_CP97) Near 3V peak, more than enough to properly detect. Importantly, with this level, a single lamp might be sufficient, and there is still 3! C) AF # 1 grid (PG_CP99) There are some 20V peaks ! It's too much, this lamp must be completely saturated. D) grid of the final AF # 2 (PG_CQ05) peaks over 200V ! Needless to say that the entire AF stage is saturated and this explains the reaction: the power supply can not work well. *********************************** With these results, there is simple test to do, if the gain is too strong, it is sufficient to decrease it .... by removing a lamp! Just replace the AF # 1 lamp with a 10nF condenser 10nF between its grid and anode, so, no amplification for this stage. The result is quite satisfactory: the sound is good, there is no reaction, we can settle the 2 rheostats with flexibility and progressiveness, in short, the set works better. It should be noted that in order to achieve this function, you have to put the 99-A in LO stage and no other lamp is suitable for this stage! (nor the 99-E) That means that I must study another lamp specifically for this function (in fact, the 99-A is wired with a resistance between grid and anode 2, but not the 99-E) However, the 99-B may replace the 99-D at the three remaining slots (RF, IF#2, Det) Similarly, the 99-E is better in final AF#2 than others that work anyway (but with more distortion) Here is the radio set with lamps: (PG_CQ06) 24. making again a new ersatz. The idea is to try to find a substitute that could be suitable for all slots, including LO stage. I tried a 3D6 according to the following drawing: (Ersatz-99f.pdf) This substitute is suitable everywhere except in LO stage! Note that the gain is lower than 99-D, for example, which means that if I put 6 ersatz like this one on the radio, I would resolve perhaps the problem of gain. But it means that I need to build at least 4 subsitutes ! Why is the 99-A only suitable as oscillator? That needs further investigation ... So I installed the oscilloscope on coils of the oscillator (the hot wire connected to the varcap), and I observed the signal. First, when the reception is blocked, it is not because LO is blocked, but at this moment, the signal is polluted by a 42 kHz modulation, in other words, IF stage reacts ! This reaction does not depend on the LO lamp, but on this at RF-IF#1, and does it makes sense: This lamp has 2 functions: RF amplifier and IF amplifier. In short, the receipt is correct when this lamp hasn't too much gain. So I installed a 99-F at that position, and with this condition, I can put into any lamp at LO stage (99-D 99-A 99-F) However, as soon as it's a 99-D at RF-IF1, everything goes wrong. This version has too much gain. I think I will give it up. So here is the used lamps set: 99-F 99-F 99-A 99-B 10nF cond. 99-E For best reception, -C vlatge has been set at -10V. This is logical, versions -F use an 3D6 which works perfectly with this bias, which is not at all the case for 2SH27L used in the version -D. I even put a 99-B at AF#1 instead of the cond, and it remains some saturation, but not as much. I think that if we put in versions -F at detection and AF#1, it should work. Well, I still have to make two other versions -F substitutes. Here are the 4 manufactured ersatz "99-": (PG_CQ07) With these 4 lamps installed at RF, LO, IF and Det, we have good receipt, although the heating voltage decreases: indeed, the power supply can't give more intensity, it's time to build a stronger power supply ! Moreover, we must build this power supply which will be dedicated to the job and that I can permanently installed in the compartiement batteries. Here the set with its lamps; at left side the four "99-F" and right side the "99-A" and "99-E": (PG_CQ13) 25. Fabricating a power supply. This supply must provide: - heating voltage (originally, it's 4.5 V 360mA) - bias voltage (originally, it's -4.5 V, in series with the 4.5 V heating battery) - anodes voltage (45 and 90V) It is not necessary that the heating voltage was 4.5 V because the original lamps and my own ersatz need only 3V; Consequently, we can take a 3.5V for heating with a maxi intensity charge about 700mA (each 99-F ersatz consumes 110 mA) The bias voltage is adjustable, because I want to see its impact on the radio set working. Initially, it was -9V; During testing ersatz, I was able to set this voltage sometimes at -10, sometimes at -7V. I expect to be able to set this voltage from -12V to -5V. This supply needs no intensity. Anods voltage will be fixed at 90V, which may charge about 20 mA, and an adjustable voltage from 20 to 50V for the detector anod. Indeed, I could see that the detector voltage had some influence on the operation. This supply should be able to charge about 2 mA. Here is the power schematics. (Alim-2357.pdf) The settings will be available at the rear of the set, opening the battery compartment door. The mains cord will pass through the bottom hole of the cabinet and can be completely retracted into the compartment when the radio is stored. I wired the model on tests bakelit board. It's fast and this will allow modifications. The connection of the 5 wires be done with the original connector. It's very oxidized, it should be cleaned. It can be disassembled because it is made of 2 parts joined by a screw, holding the 5 contacts: (PG_CQ09) Each contact is deposited and cleaned with diamond cutter. (PG_CQ10) The 5 wires are now soldered to the reassembled connector. (PG_CQ11) Here is the power model (PG_CQ12) Results. The radio set works perfectly with this power. There are no more reactions or snoring. However, it sometimes happens Larsen, it seems caused by the detector lamp, which is really microphonic, by reaction with the HS which lies on the same board. It remains to be seen, once the chassis installed in the cabinet, therefore suspended by the 2 rubber blocks, if Larsen always occurs, in which case it will be remedied. The best settings for a correct receipt are: Baterry = 6 Volume = 3 - C = -9 V +45 B = +35 V Under these circumstances, tensions are measured: +90 B = +98 V VA = -3.5 V (output heating supply) VA General = -2.37 V (heating lamps except detector) VA detector = -0.8 V (heating of the detector) I90B = 16 mA (total anodes intensity except detector) I45B = 1.1 mA (detector anode intensity) IA = 0.4 A (total heating) Comments. The optimal value of C is really -9V as original; it proves that the lamps (3D6) need the same bias as the V99's. The anode voltage for optimal detection is +35 V instead of +45 V, but the difference on receipt between the minimum (20) and the maximum (+50) is not really significant. The detector does not really need much heating (0.8 V)! The intensity of 16mA anode is quite correct. We could use a fixed bias of -9V by using instead of the 1k potentiometer, 470 and 750 ohms resistors, only a single 560 ohm resistor(9 / 0016). Similarly, the voltage for the detector could be set at +35 V by a resistors divider bridge, to remove the knob. Here is the simplified power unit schematics: (Alim-2357-simple.pdf) I used standard components, easy to find: -- Transformers: one that delivers 2 x 24V under 3VA each, the other one delivers 2 x 6V under 6VA each. Of course, you can use other transformers, such as a 48V / 6VA , 12V / 12VA and so on ... -- Capacitors are found in PC power supplies. The 680µF and 220µF are 200V insulated. The 100 µF, 25V insulated. The 3300 µF, 16V. -- Integrated regulator is a LM350 in TO220 case. A LM317T could agree as well. It needs an heat sink. -- Diodes are all 1N4007, but may agree 1N4004. -- 27k resistors are 1/2W (or two 56k 1/4W in parallel), the 2.2 k in series with the +90 B is a 2W; the 560 ohm is a 1/2W. All others are 1/4W. Tensions and intensities indicated on the diagram were identified with the radio in operation, and Battery on "6", Volume on "3". Now that power unit is finished, it's time to make connections to original connector. I added a terminal on the power board, now I can disconnect it to replace or to check it without having to disassemble the connector from the cabinet. Here is the whole power unit-connector: (PG_CQ16) On power unit, I stuck a label identifying the terminal: (PG_CQ17) The original wires have been shortened to the same length and the metal tags have been cleaned: (PG_CQ18) 26. Failure. During testing the power unit, cracks have sometimes occurred. I first attributed them to a poor reception, but as testing continued, they increased in intensity. Here is a description of the symptoms: - The receipt is now impossible without interferences covering completely sound. - When you unplug detector lamp, you can hear in HS a noise loud enough , which seems random, with bass tonality. - When you remove the lamp BF#1, the noise disappears. I first thought that AF transformer T10 between the 2 lamps was out. - When you bypass the primary winding of the transformer (between the +45 and detector anode), the noise disappears. - When you measure the voltage drop at the terminals of the 2.2 k of the power supply +45, detector lamp removed, you get: 0.27 V. Conclusion: the capacitor C2 leaks. You can even evaluate his leakage, the open circuit voltage is 83V. The current is: 0.27 / 2200 = 123 µA. So the leakage resistance of the cond. is: 83/123µA = 676kohm! We must change this capacitor, because if it's been in short-circuit, there is danger for the primary transformer T10, which will be directly connected between +45 and the ground (however, the internal resistance of power supply would limit the current, but do not risk is better ...) So, I have to disassemble Catacomb again! Well, This Catacomb is removed, shield removed too. I decide to change C2 and C4, which are side by side. I used 150pF/250V. I had to lengthen one leg to connect the cond on each side. Here capacitors wired: (PG_CQ14) (PG_CQ15) Reassembling can start ... Duration of the repair: approximately 1:30! Tests: the failure has been repaired, the noise no longer manifested if we remove the detector lamp. A voltage measure on 2.2k shows there is no current output when the lamp is absent, proof that the new cond does not leaking. The reception is again correct, its level is stronger than with the original condensator. 27. Reassembly of the entire radio If the cabinet restoration is complete (wooden), we can begin to reassembly the radio set. It must first fix parts like door, the HS grid, contacts of the antenna ... There was no real order reassembly, with the exception of common sense! So I started to repair the hanging system of the speaker grid. This system is made of 2 axes on the grid and 2 eyelets inserted in the wood. The axes must enter eyelets, locking is made of 2 elastic latches below the horizontal partition. I had to glue one eyelet rivet that was ripped. (PG_CQ81) glue 2 nails into holes of the grid. The nails exceed about 5 mm (PG_CQ84) Latches are cleaned rested under the partition (4 screws) (PG_CQ83) Initially, there were 2 small rubber pads on the edge of the partition so that the loop antenna box will not damaging the wood by rubbing when the door was closed. Of course rubber was out; so I pasted 2 small pieces of felt. (PG_CQ85) I screwed the 3° speaker support. (PG_CQ86) I polished and reassembled rear contacts of the antenna (PG_CQ87) (PG_CQ88) The lock also has to be polished, and the inside plate and the heads of the screws (PG_CQ89) The lock is screwed on the door: (PG_CQ90) On the other side: (PG_CQ91) Hinges when cleaned and polished are screwed. I changed the screws: I used brass conic head screws M2.5mm x12 (ISO) (PG_CR14) The piece next to the lock was also polished: (PG_CR16) The parts that were used to contact batteries may not be used as they are now unnecessary: (PG_CR29) 28. Making new screws When I get the radio, missing 5 screws on the front panel. There is 9 screws: - 5 are used to retain wood front panel on metal panel. These ones are short. - 4 are used to retain radio chassis in cabinet. These ones are long. So, the 4 longer screws and only one short screw are missing. We must therefore find these screws ... The problem is that these screws have a round head of 10 mm in diameter and are made of brass. So I decided to refabricate them. The principle is simple: solder a round head on a normal screw. There I was lucky: indeed, the original screws had a diameter of 5/32 ", very close to 4 mm. On the other hand, the thread is 1/32 "(very close to 0.8mm), while the european ISO M4 screws have a 4 mm diameter and a 0.7mm thread. In other words, screw 4mm must enter virtually into the tapped brackets, which are pieces of metal about 2 mm thickness; with the difference between the two thread, the screw sould not be blocked. Indeed, we can screw a screw M4 virtually the length of support. So it needs to use a M4 tap into the brackets so that the screws drive well: (PG_CR17) (PG_CR18) I take this opportunity also to tap the 5° hole on the front: (PG_CR19) Here is the equipment to make theese screws ... Brass screw diameter 4mm, at least 30mm length, and nails used for decoration with head 10mm and indifferent length. (PG_CR20) We have to start by removing the nail of the head (PG_CR21) Then solder the head of the screw in the head of the nail, put enough soldering and testing perpendicularity between head and screw. (PG_CR22) Then, it is necessary to make the strait of the head with diamond disc: (PG_CR24) (PG_CR25) Where is the new screw? (PG_CR27) Just to finish cut off the screws to the right length: 4 screws with 27 mm 1 screws with 14 mm (head excluded) (PG_CR28) 29. Continuing assembly The tapped bracket have to be fixed on corner tassels (PG_CR30) When I get this radio, the handle was missing. Here's what it looked: (05aa_12) It should be removable, which explains why few radios are now equipped ... At first I tried to see what I could do from an existing handle (PG_CR31) This one is too short and too wide, it's inappropriate! So I decided to do a remake. It will not be removable, which is not so bad. It must be 15 mm wide and about 18 cm longer (between the 2 axes) In the meantime, I polished the cups and head screws (PG_CR32) We can also install the mains power unit. We must put three screws (4mm diameter, 40 mm length) on the partition. (PG_CR33) 3 nuts are used to raise the circuit from partition. The connector has been fixed on the connector; here is the power supply installed: (PG_CR35) There is enough place at the back of the cabinet to store the mains cord; Running, it will go through the hole drilled in the body. We should make a wooden box to hide the modernity of this power supply ... Super, I went to the shoe-maker who made the handle to me. I put it soon on the cabinet: (PG_CS24) Of course, it's not removable, but it's better than anything. The reassembly can finally be continued. All is need is resolder the antenna wire on the upper hook (PG_CS27) then put the insulation paper (PG_CS38) It is better to change the portion of wire connected to the hinge; a simple wire in a piece of isolated tube, a splice covered with adhesive tape and the wire is inserted into the hole: (PG_CS28) The radio chassis can then be positioned back. First power connector must be inserted (PG_CS29) and the 3 others wires through the central hole of the partition (PG_CS30) and drag them from the battery compartment. At the same time, we let slide the chassis into his housing. (PG_CS31) (PG_CS32) sIt should be checked that the 3 wire and the power strand is not wedged. we can then screw the 4 new screws to fix the radio chassis. (PG_CS33) The 2° wire of the antenna must be passed through the partition. (PG_CS35) Same manner than the first wire of the antenna, it is necessary to change the last centimetres with new wire. (PG_CS39) This one is insulated with adhesive tape then slipped into the hole. (PG_CS40) The 2 wires of the horn speaker is passed too through the partition (PG_CS36) and connected to the speaker. (PG_CS43) The Hs is fixed on the partition with 2 screws. (PG_CS44) We can then put the frontal grid of the speaker. (PG_CS45) The 2 wires of the loop antenna are cut leaving 3 cm length. (PG_CS46) then they are stripped and soldered on the 2 hinges of the door. (PG_CS49) The 3 hinges are then screwed on the cabinet (6 screws) (PG_CS50) (PG_CS52) It is then necessary to check the operation of the lock. Of course, after these years, the positioning of the door is not very good. I had to adjust by unscrewing the hinges a little, by shifting the door slightly. After some tries, the door is well aligned with the cabinet. The lock not functioning well, I had to add a hold under the pawl, so during closing, we haven't to press on the button, the door locks itself when it is pushed. (PG_CS53) Then, I ground a little the trowel of the door, as well as the pawl so that the opening was possible. It is necessary to make these fittings without antenna case to be able to see and reach the lock inside the door! (PG_CS54) When this is done and the door can be closed and open correctly, we can put antenna case in the door and carry out the tests. 30. Tests It is enough to connect power unit on mains and turn the button… and radio wonderfully works ! There is just a problem with antenna contact: when it's swivelled, the reception disappears and appears. By looking at there more closely, I realized that the point contact of bottom is unset: the cone moves slightly on the washer. It is necessary that I see that. (PG_CS55) the best is to dismount the lower screw of the pivot. It is necessary to remove filling wax (PG_CS77) and we reache the nut which is soldered with the wire (PG_CS78) once the unsoldered wire (PG_CS79) and the removed soldering, the nut is unscrewed (PG_CS80) and the screw can be removed on the top. (PG_CS82) I put the screw in the chuck of my drilling machine (PG_CS83) and I have polished (with sandpaper increasingly small grains then with steel wool) The reassembly is done by adding a washer because I had noticed that even when the upper screw tightened thoroughly, it remained play. (PG_CS85) Once the tightened screw, the wire is again soldered. (PG_CS84) It is necessary to carry out a test before filling wax in the hole. The test is conclusive: while swivelling the antenna, there is no more losses of reception, proof that the contact is correct. I tested the radio with the antenna fixed on the rear hooks, and it works well. Obviously, the disadvantage is that is necessary to turn all the cabinet to receive the maximum of energy. 31. Conclusion I hope this a little long report will have intessed you. Here the last schematics of the radio set: (schemab.pdf) if you need explanations for the frequency converter stage: (explanations-f.txt) and here are some photographs… The closed radio set (PG_CS72) (PG_CS74) We open the door and we discover... (PG_CS61) (PG_CS62) the open door with the swivelled loop antenna (PG_CS69) (PG_CS70) (PG_CS71) some details (PG_CS56) (PG_CS57) (PG_CS58) the radio with its antenna hooked at rear (PG_CS67) (PG_CS68) the radio put on its table (PG_CS76) I'm not an expert in english, so it's possible that I used wrong words or expressions. If you find translating mistakes, please, send me an email and indicate to me the right way! Pierre