Hi Arran.
I continue to disassemble and I see that the interstage transformer is completely beyond repair. It is placed in an iron box and completely filled with bitumen. There is no way to clean and rewind it. But I plan to use for the first step the circuit upgrade we discussed above with a symmetrical choke instead of a phase inverter transformer. As a choke I plan to use a small 120-240V converter transformer, I have a couple of them, it should be popular for this purpose. In the future, I may find a ready-made transformer with a combination of about 120V + 120V + 120V or something like that. I can apply a similar method to the output transformer. I have changed similar parts several times to fix the problem of a broken output transformer in several of my portable tube radios. In this case, rewinding is extremely difficult, as the audio transformer in this radio is very small and has a huge number of turns of very thin wire. For this case, I used with good results a 120v x 6-12v power transformer from an old power supply from small devices such as a phone charger. The winding data for this transformer matched the original requirements quite closely.
If you want to work, lie down and sleep, and everything will pass.
Vlad;
It's possible that the tar/bitumen using to pot the box may have lead to the failure of the transformer, either that or the paper insulation, one or both may have been acidic, or hydroscopic, and corroded the wire. One nice feature of the metal box is that a more modern replacement transformer, or choke could be hidden inside. I think I melted the tar out of the box upon the suggestion that it could be repaired, I even went a step further and attempted to peel the paper back to find the break, I did not get very far. Somewhere I have a plastic container full of the laminations from this transformer, which I had the idea of maybe finding a substitute transformer bobbin that would fit the iron. The choke substitute is an interesting idea, though you do loose some element of amplification, I think I worked on a Canadian Westinghouse set that had a similar arrangement to your family battery radio from Ukraine, I never thought that the Soviet equivalent of a 1N5G could be used for audio output tubes.
Regards
Arran
The chassis is ready for the next steps - cleaning, repainting, restoring dead components.
All dead parts are removed and disassembled for restoration, also the some chassis parts are removed for separate repainting.
As I expected, unfortunately, both audio transformers have open coils. This will be a big headache for restoration. But as you can see in the message above, for some people it is not a big problem .
Also, all the capacitors are bad. All of them show a maximum resistance of 0.5 - 1 mOhm. But repacking them is just toys with a transformer problem.
But the good thing is that the speaker is in excellent condition.
Okay, the next step will be cleaning and repainting all dirty and rusty parts of the chassis and repacking the capacitors.
I will continue to report on the restoration process.
If you want to work, lie down and sleep, and everything will pass.
Today I tried to restore the output audio transformer. The primary windings were completely open. Usually in 50% of cases, in my experience, such a problem is a consequence of corrosion of the soldering points of the primary wires with the output terminals or wires. Usually the ends of the windings are brought out to the outside of the coil, and not inside (in this case, only a complete re-winding can help) and already from the outside they are soldered to the terminals.
Okay, I'll try.
First, I disassembled the transformer and removed the top layer of insulation.
Yes, I was right. The soldering points are completely eaten away by green copper corrosion. New additional connecting wires were created for soldering the very short remains of the ends of the windings.
Soldered them all
And ...
Yes, now they are not completely open, but the resistance is about 200 kOhm - 1 mOhm.
In any case, apparently, there are corrosion breaks inside the windings. There was no easy way. More brain-twisting and headaches will be required.
Fun continue.
If you want to work, lie down and sleep, and everything will pass.
(This post was last modified: 06-24-2025, 10:33 PM by Vlad95.)
I found a way to solve the problem with transformers, but I'll deal with them later. Now I'm starting to restore the capacitors. As a rule, I don't like the standard method of simple "recaping". In my opinion, this is a way to destroy an old radio. When I see the result of "recaping", I want to cry over a dead radio that lived for 70-100 years and was eventually killed by a careless hand.
But all of the above is just my personal humble opinion.
So, I'll start the report on the restoration of the capacitors. As I already mentioned, all the capacitors were either completely open or had a large leak. Except for a couple of mica ones.
This is an electrolytic capacitor
8.0+8.0uF x 450V.
Paper capacitors are:
1.0+1.0uF x 650V,
2 x 0.5+0.5uF x 650V,
0.1uF x 650V.
If you want to work, lie down and sleep, and everything will pass.
Let's open up the large electrolytic capacitor.
Carefully flare the case with a screwdriver, a wooden mandrel, pliers and socket heads to align the edges of the case.
And remove the two rolls of foil and paper.
The output connections are aluminum and will be replaced with solderable parts.
If you want to work, lie down and sleep, and everything will pass.
The square paper double capacitors were disassembled using a heat gun and a few handy words.
The small 0.1 mF capacitor was easily disassembled using pliers and a small hammer.
If you want to work, lie down and sleep, and everything will pass.
All capacitor parts were straightened and cleaned. The following parts were selected to replace the capacitor internals:
electrolitic caps - 22uF x 450v
ceramic caps - 1.0uF, 0.63uF, 0.1uF x 650v
If you want to work, lie down and sleep, and everything will pass.
Vlad;
Have you thought about using non polarized film capacitors, or motor run capacitors in place of the electrolytics inside the filter can? Bob Andersen, and a few others have restuffed old electrolytics with these so they don't have to deal with the filter caps ever again.
The biggest issue with returning an older radio to a "near original state" is replicating the body-end-dot coded "dogbone" style resistors, unlike with bypass caps there really isn't any way to restuff them, so replicas would have to be made.
Regards
Arran
I thought, thought and decided. The previous ones lasted for almost 100 years. These ones will also last for 50 years. I am 75 now. So when I turn 125, then I will think about replacing electrolytes with longer-lasting film ones.
If you want to work, lie down and sleep, and everything will pass.
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