A few years back I bought a radio from the Soviet era. It has the Russian markings and so on, but the valves are standard octal types. It also has a tuning indicator that doesn't work.

The volume seems a bit low, and I noticed that the 6SQ7 triode is not used at all (the diodes are connected). Do you think it would be ok to hook up the triode to give a bit more oomph?

Also, the tuning indicator lights up a pale green, but there's no sign of a shadow. I was thinking maybe the resistor to its inbuilt triode could be open circuit. What do you think?

Anything's possible, there was apparently pressure to get those things out the door to meet quotas despite missing parts.

Do it!

Send photos buddy

The resistors on a tuning indicator have an attrition rate, like wax paper caps, never to be left unchecked. We also have the issue of no AGC voltage.

Marc

If the reception is weak, there is likely a problem or problems in the front end. These can be anything; misalignment, resistors gone high, faulty valves, I.F. transformers lost their "Q", open windings, leaky capacitors, capacitors with high ESR, especially mica types, etc. Dozens more possible causes. It is puzzling that the triode part of the 6SQ7 is not connected. Is there another audio driver used? Is the 6SQ7 the correct valve for that socket?

A good thing to check is if AGC voltage is being generated. If it isn't, see above. That would also be an explanation for why the tuning eye is not working.

Cheers, Stuart

No problem with reception, it's just the volume is a bit lower than i'd expect with the number of valves it has.

I don't remember what pre-amp is in use. I'll need to look when i'm down there next week.

The greatest cause of "deaf sets" relates to alignment: What is often overlooked for on, is the recommendation by manufacturers, to re-align if RF parts have been changed.

2nd comes with the test equipment itself. I have just made up a test strip for a Mower / Small Engine shop, that will allow the meters to be quick checked against known resistances and two HV caps to check the calibration of the ignition capacitor testers. I have replaced one old DVM meter recently as it went out of calibration.

Then there is the signal generator. Mine is stable but correlation between output frequency, band spread & the dial are another matter. So it is calibrated with a frequency counter: Even that presents a trap. There are two counters here, that will be very, very wrong, should you dare have the tone / modulation turned on when you set the frequency.

Tuning indicators are a good indicator of serious issues up front and in the IF train.

Photos sent to Brad.

I had a look, and found the reason the tuning indicator didn't show a shadow is that the socket wasn't wired correctly. In fact the wiring did not align to any valve I know of. I did some experimenting and found that a EM34 works well, once the socket was rewired. However it came with a 6U5G (unknown if this is the intended valve), so in the end changed the wiring again to work with that. I did notice that the triode in the EM34 has 3 times the gain of that in the 6U5G, when expressed as voltage swing on the anode.

The next problem, as some of you already guessed, is inadequate AGC voltage, only managing to get -1.2 volts on 2RN (the former 2FC), the strongest station out there. So, in the end, the 6U5G shadow never moves. The radio looks quite complex, being full of green resistors with small type-written values printed upon them. I feel I'd need a schematic.

The valve line-up is: 6SA7GT, 6SK7GT, 6SQ7GT, 6SJ7GT, 6V6GT, 6X5GT, 6U5G.

Sensitivity-wise, it picks up everything I'd expect of a valve radio, but the volume isn't controlled as well as I'd like, due to the inadequate AGC.

Sounds like it's low in gain which, with that valve lineup, it shouldn't be. First, have a look at plate and screen voltages - you might have a screen dropper resistor that's gone high or a leaky bypass cap or 2 or 3....

6U5 needs around -22V Grid bias

EM 34 is a Dual sensitivity type Minimum shadow Angles at -5 V and -16V

It is very unusual to find the 1M resistor on them good. Miss wire is different.

Photos uploaded to Post 8.

Thanks Brad.

My questions are: does anyone recognise this radio, and can someone give me a schematic of it?

There are odd things about it and I am wondering if its an under licence job? The tuning gang is more like the Stromberg Carlson types and Philips were one that used big cable drums like that.

The photo of the logo is too grainy to read and I would expect CCCP on it if it was built in Russia itself.

A photo of the inside of the pan may be useful?

There is always reverse engineering, which is why I bought the AutoCAD decades ago.

I asked a friend in Ukraine to identify the radio.

Its a Baltica made circa 1950-52 either in Riga, Latvia or Kharkov, Ukraine.

https://www.radiomuseum.org/r/zilgorky_baltika.html

you will find circuit diagrams here .. looks like there are 3 variants :-

https://www.gstube.com/schemes/

Hope this helps

Nhanwell, thanks very much!

Looks like the Baltica52 is the closest to what I have.

Now I'll be able to find out what's going on. I might even be able to find out why the long wave band is so insensitive.

Going by those photos, I'm missing the back panel, also the valves are completely different shapes to mine. But maybe they are equivalent.