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

[Murphyv310]

Actually a quote from my old lecturer at college, told me to put it away and once qualified would be a professional!!!!

I think the reason was he had a couple on his courses and they disrupted the routine.

[Nowhere-Man]

At the moment I grapple with radio related material at night. However today I need to buy some water based paint. Last night I was curious about the average collector current in a vintage tranny. I winded up looking up the AF177 in my reference book. It listed 10 milliamps. I was trying to just envision a typical scenario. Before I go and shop for paint I should add I have some very detailed data sheets on the P423 transistors supplied by the moderator of the Russian site. He told me the P423 is considered pretty mediocre by the Russian enthusiasts. Maybe a bit like we suspect the AF117.

[Nowhere-Man]

By the way that bomb attack in St Petersburg was where I lived in 1997. It was metro station Tehnologicheskiy Institut. I used that metro all the time. Apparently 13 died and many wounded.

[ppppenguin]

The AF11x transistors were certainly not mediocre. They were high performance parts for their era and still do a perfectly good job in their intended applications. The AF114 was the best, AF117 worst, presumably done by selection from the production line. It's unfortunate that they were later found to suffer from tin whiskers. Once the whiskers are cleared by one of several well known methods they usually carry on working OK.

NB: The AF118 is a special case. I don't know if was selected from the same production as the others.

[Cardigan]

I'd second what was said in the post above. The AF11x family were the gateway to making VHF transistor radios a reality, so in no way can be classed as 'mediocre'. I have wondered how the OC170 family relate to the AF11x family.

[Murphyv310]

Totally agree about the AF*** range. The performance in British made sets of the era was quite remarkable. Just a pity they did have the whiskers issue as otherwise they are extremely reliable.

[ppppenguin]

The OC170 family were the first VHF capable transistors readily available in the UK. Immediate predecessors of the AF11x. I presume the AF11x were an improvement.

[Nowhere-Man]

However the case may be, the moderator didn't rate the particular P type transistor I referred to. Maybe he was being a bit harsh but he indicated they were a sort of an early attempt. I have found a few links to the VEF 12. One is a complete circuit commentary in Russian. If I ever find time, maybe I'll translate it into English (why not?). In the meantime, maybe an online translator can do the same thing. Here is the link and it gives a schematic too:
http://kot-ivan76.livejournal.com/307493.html
Is there any reason why putting your finger on the case of an HF transistor would cause shrill whistling? I know people have tapped AF117's and this alone caused a dead radio to revive.

[Murphyv310]

If the metal case of a transistor is not grounded it can basically act like an aerial when you touch it, thus giving all sorts of whistles from pick up. You get this effect on AF117's if the screen is cut off.

[Cardigan]

If the metal case of a transistor is not grounded it can basically act like an aerial when you touch it, thus giving all sorts of whistles from pick up. You get this effect on AF117's if the screen is cut off.

I've had the issue where cutting the screen lead restores life, but with instability. I have never tried reconnecting the screen back to its 'earthy' connection via a small capacitor - I suspect that will kill any signals but I wonder if anyone has tried it?