ВЭФ 12 (Astrad VEF 12 Project) - including a transistor tutorial

[Nowhere-Man]

I will shortly continue with the transistor "crash course". The Russian radio hobbyists gave me a fair bit of feedback on the VEF 12 but threw a lot of technical jargon I needed to translate. The turret they refer to as a "baraban" Russian for drum.
All of this sometimes overloads my brain and I get blocks. Guess I need to learn the technical terms.
I may soon print out a ARRL transistor circuit we can look at and discuss. Note that then in 1960 transistors were seen as useful but not a replacement for the valve. So the depth isn't overly deep.

[Nowhere-Man]

Today I messed about with transistors with books left aside. I tested some 0C44 transistors in a very simply made Bush radio. I was very impressed with the way they made stuff back then. Nicely sized transistors solidly point soldered on a robust chassis. Simple and reliable circuit. Transistor testing was fairly easy. Funny but if I put my finger on one of the Soviet transistors, it bursts into whistles. Not these mullards.
I tested some more AF117's (removed from use) and they test OK at the junctions.
Much to be learned though.

[Murphyv310]

Hi.
Some of the early Russian transistors were far less stable than Mullard and others from the west. The Russians were behind us in semiconductor technology in the 60's. Valves though were their forte and they definitely were the leaders in the pack till probably the 80's. The Rod Pentode's being the culmination of all their research.

[Nowhere-Man]

The USSR economy was always lagging in some areas but rocket technolgy was always strong. Having actually watched a Soviet CRT TV I can clarify they were superb but weigh a ton. They were built for purpose and not for marketing. I am told under Stalin factories would be given a production target and, if it wasn't met, charges of sabotage could arise. So, work was rushed. A few shortcuts as well.
Also (and this is actually true) I recall having my photo taken in Russia back in 1992. It was for an ID pass. I was asked to sit down and look ahead. The next thing I knew this guy appears holding a giant monstrosity with bellows and funnels attached. Looked like something from the 1920's. There was this huge flash and I was left dazzled.

[Miguel Lopez]

Having actually watched a Soviet CRT TV I can clarify they were superb

Have to disagree at this point. We had a lot of Soviet CRTs in Cuba both with valve and SS TV sets. Althought the CRTs which came with the set from the factory lasted several years (about 10) , when you had to replace it, the replacement used to last about two years at best. At the same time there were in Cuba many Western TV sets from the 50s with the original CRT still fitted, so I don't think that the Soviet TV CRT should be considered as very good. My opinion.

I'm agree about the weight. A friend of mine who studied in the USSR, told me that all the Soviet productions were measured in tons, so the annual production of TV sets was X tons. Maybe that is the cause for any Soviet stuff being so heavy.

[Nowhere-Man]

I suppose Soviet production didn't face much competition in an international market so emphasis was on practicality. When I lived there I had to queue for food and amazingly the shops just had "PRODUCTS" painted on the entrance. Anyway, our radios were built in an era when the USSR was leading the space race (Valentina Tareshkova was 80 yesterday). I guess the said radios reflected optimism within the country.
By the way, Miguel, are the transistor legs of the VEF soldered to the board through the sockets or do they pull out of the sockets? I did test all the legs are OK and I wax sealed the ferrite windings. These tested fine for continuity but had to be resoldered, tidied and waxed. It was fiddly and I had to scrape the ends of the windings before soldering.

[Miguel Lopez]

None of my VEF-20Xs have sockets for the transistors. I think the Soviets abandoned that way of thinking by the 70s. I just have seen sockets on my Spidolas and one Selena-206 that I repaired. I think that if they used sockets, it should had been to avoid soldering.

[Nowhere-Man]

Here's a question: The red square capacitor Miguel warned is best to be substituted has the marking H90 33H. In Russian "H" is the term for nanofarad (because "H" is pronounced as "n" is, say, "nut". So, I am fairly sure the red square menace is 33 nanofarads. At least, I hope that's correct.
Fishing around on my boat I located a spare capacitor marked 2A 333J. I estimate this to be also 33 nanofarads. It's rated up to 100 volts and smaller than the red square menace. Do you reckon it will be OK? I was going to go to Maplin but maybe this will suit my purpose.

[Crackle]

Is it C61? If so then it looks like it is decoupling RF in parallel with a 20uF electrolytic C60 on the supply to T5 & T6. So its actual value is probably not all that critical. To be honest unless you know it is faulty I would think it is not going to need changing. Foil capacitors, even wax paper ones, normally leak very little in these low voltage circuits. I have loads of 60 year old transistor radios all working perfectly with their original foil capacitors, and transistors. (sometimes I find the odd electrolytic that is pulling down the supply voltage to a part of the circuit)
Have you got a multimeter with capacitance function?

Mike

[Nowhere-Man]

It must be C61 as it's in circuit with the IF transformers. I doubt changing it would make any difference but the quality of the red square capacitors is known to be not so good. Changing to a better capacitor may not make any difference I guess but should be easy to do. Any idea what the max current would be as I couldn't say for sure?