Catacomb unit



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.

Photo


Photo


Photo


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:

Photo


Photo


Some cables are retained by strings that must be cut.

Photo


Photo


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)

Photo


It should also disconnect ground wires as well as those which are connected to the 2 caps.

Photo


Photo


Photo


Joining anode L5 includes 4-wire soldered together (anode-primary T11-CU-H1) must be cut the wire that goes to the front plug

Photo


Photo


The catacomb began to emerge, but there is a common thread that we must unsoldered (it connects the 2 F capacitor "BC")

Photo


Photo


This is the catacomb released

Photo


Clearly the number of this unit: C 206443.

Photo


To access the inside, remove the top sheet

Photo


Photo


And here's the monster wiring. The 6 tubes sockets form a single plate on which everything is riveted or soldered.

Photo


To extract the circuit, I tried with a screwdriver to lever

Photo


And it works: by turns at each end, the entire circuit slides out of the box.

Photo


At one point, all frees itself: here is finally unveiled inside!

Photo


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:

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:

Photo


At the lower end, C3 and C6 are on each other:

Photo


C2 and C4 in the middle of the circuit:

Photo



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.

Photo


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)

Photo




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.

Photo


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.

Photo


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:

Fichier pdf  Test

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:

Fichier pdf  IF transformer

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)


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 F. 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.





front panel restauration...