[RadioSvit]

Hello Vlad. In general, in my opinion, restoring a wooden case, even in such a bad condition, is much more pleasant than restoring a chassis that is too dirty and rusty. Washing the chassis and cleaning it of rust is the most unpleasant procedure for me, so never expect a perfectly clean chassis from me. But repairing the receiver case is a real pleasure. In my opinion, there will not be too many problems with your cabinet in terms of reproduction. First, you need to glue it and remove the old layer of varnish, and then it will become clear what materials are best to restore it with.

[Vlad95]

Since the original schematic was in an old unreadable style, I created a new schematic diagram.
Owners of this radio can use it.
The original schematic is also attached for reference.

[Vlad95]

Today I finished inspecting all the parts. The result is not very pleasing.

The first positive news:
1) The power transformer looks alive.
2) The speaker and field coil are alive.
3) The primary power capacitors C21, C22 are alive.
4) The power choke is OK.
5) All resistors are within normal limits.
6) All mica capacitors are within normal limits.
7) All lamps are most likely alive.
8) All coil include L7 - OK.

The second negative news:
1) All electrolytic capacitors C 8, 9,10,11,14,16,18 are dead (maybe not all, but I will still change them (repack).
2) Both potentiometers R11, R14 are broken (open or poor contact). I will try to restore them.
3) Most of the wires have cracked insulation and require replacement.
4) Upper section of resistor R13 - 3.6k open, but it can be fix easy.

The third and very sad news:
Both audio transformers are broken.
I'll try to rewind it, but the phase inverter transformer can have over 10,000 turns in each coil, and the wire is less than 0.08 mm
It will be a terrible job to rewind. The output transformer is a little easier, but not much.

In the end, I'll probably start with restoring the case, and in parallel, step by step, I'll restore the circuit parts and chasis

Oh-oh-oh
 

[RodB]

You can bypass the interstage transformer by disconnecting the primary, connect a load resistor of about 10k - 20k to the 24 plate, connect a coupling cap to the 24 plate to 45 grid. The transformer secondary takes care of the phase inversion. I've done this in a couple 1930s sets. Works great, and you can wait till a replacement transformer shows up. This is documented elsewhere on this site by Ron Ramirez.

[Vlad95]

Thanks RodB for the help.
But this is not a real solution to this situation, not even a temporary one. Because the first output stage will only work in single-ended mode, not in push-pull. But the output voltage setting of the tube is in "B" mode, and you need to change the grid voltage setting to switch to "A" mode. Otherwise, the audio output will be heavily distorted and very low power. And only one of the two tubes will work. In other words, it will cause more problems than it's worth.
But in any case, the output transformer is also dead and needs to be rewound or replaced. So I still can't revive the radio this way, even temporarily.

[RodB]

The output 45s are still in push-pull because the transformer secondary winding is still in the grid circuit providing opposite signal polarity.

[Vlad95]

No, you are wrong, because you did not know the details.
Unfortunately, only ONE winding out of six is intact in both transformers - the secondary in the output transformer, (which is not surprising).
All other windings are open.
And no such solution is possible without replacing the transformers. But if they are to be replaced anyway, then they must be replaced completely.
 

[Vlad95]

By the way, the bypass you suggested is a rare solution in some circuits.
For example, this schematics solution is used in my radio receiver "Rodina-47" made in the USSR. You can see it here:

Rodina-47


[Image: https://www.radionostalgia.ca/My_collect...ematic.jpg]

[RodB]

Ouch! Not often the secondary takes a hit. Wish there was a better solution. I have a good interstage transformer but it's from a Philco 650.

[Arran]

Vlad;
I looks like your set has the same problem that mine did, both a bad output transformer, and a bad audio interstage. I suspect that some form of corrosion was to blame. I think that I even took the interstage transformer apart hoping that it was just a broken wire but no luck. There is a solid state substitute for these that was published in the Antique Wireless Association "Old Timer's Bulletin" but I cannot vouch for how well it works verses a proper transformer. Hammond does make a substitute interstage transformer, and Antique Electronic Supply does sell a generic one, made in Mexico.
Regards
Arran

[Vlad95]

Thanks RpdB
I don't think there's much difference with interstage transformers of different models other than dimersion. But I try to localize the problem internally first.
In my experience, the most common cause of thin wire breakage is corrosion at the solder joint to the output wires or lamellas. These terminals are usually on the outside and can often be found and repaired.
Also, I'm not sure shipping to Canada is easy. But if I did not fix it I will contact with you about transformer.

Arran, yes, finally if I did not get fixing result I will look on market for transformers.