Hi transistor fans- I'm mainly a tube guy, and in spite of working on transistor broadcast equipment all my life I've never really gotten into repairing pocket-sized transistor radios. But I have a number that I'd really like to see playing, what with the baseball season coming up. May I ask a few questions?

1) I know that anything can go wrong with an electronic circuit, but by and large are bad 'lytics the most common problem plaguing transistor radios? Does replacing 'lytics revive a majority of dead or weak transistor radios?

2) Do these radios use 'lytics mainly after the detector or are they used in RF/IF stages as well?

3) Is it common for old (45+ years) germanium transistors to become leaky or otherwise bad?

I thank you in advance for your guidance! Bob

...bad electrolytics are among the major things that can plague transistor radios. They are rarely found outside the audio section (occasionally in the AVC line) except in AM/FM radios (there is usually one in the FM detector stage) and are used in the audio section as coupling/DC blocking capacitors (something rarely, if ever, encountered in tube radios), as well as bypass capacitors. And in transistor radios, because they run at much lower voltages, they tend to fail in a different manner. Rather than shorting/leaking (with often disastrous results) like in tube radios, the overwhelming majority of electrolytic failures in transistor radios stem from drying out and going 'open'. This causes weak or no sound.
...and oh, yes, old germanium transistors can also be failure-prone, especially those that are in metal 'cans' and have a fourth 'shield' lead connected to the can. This is well documented in this forum (searching 'tin whiskers' should get you some older threads about this); in a nutshell, they tend to develop internal 'growths' that extend from the germanium out to the 'can' and short to it. Germanium transistors also were 'weaker' than silicon, that is, they could not handle the voltages and/or currents that later silicon types can. Generally, it is not possible to substitute a silicon transistor for a germanium transistor without extensive re-engineering of the circuit...

1. Yes

2. After

3. Not really

The vast majority of problems with transistor radios are caused by bad electrolytics. They are used mostly for coupling in the audio stages but also as battery bypass and AVC filtering/timing in the circuits leading back to the RF and IF stages. A bad electrolytic as part of an FM ratio detector is often a problem. Finding leaky germanium transistors in old equipment is not an everyday occurance but you can't rule out the possibility. The failure mode mentioned earlier (tin wiskers) is very common.

Dave

electrolytics everywhere even across the battery. I am working on this model. as you can see there is a 50uF sort of across the battery through a 150 ohm resistor but its there. this one had a bad audio output transformer that I am fixing

From the point of view of a repairman who was there in the 50's as pocket sets came on line
the problems were equally divided between transistors , ( germanium oscillator/ convertor and I.F.),
drop problems, and battery terminal/leakage.

Convertor transistors were hard to get for off-brand imports, and the American replacements
were too big to fit easily (top hat transistors).

Drop issues were broken wires to the ferrite rod , earphone jack, power switch contacts,
and pcb breaks.

About the only issue after the detector was short battery life because of leaky output transistors
or issues with the thermistor in the base bias circuit.

Sometimes the large electrolytic across the battery rail would detach a lead after a drop.

I would mildly disagree on the topic of the germanium transistors. My transistor repair experience has been mainly with Transoceanics with some lesser Zeniths from the same era. After maybe 8 Royal 3000s and 4 1000s that I have worked on for myself or others, I have found at least one dead-failed transistor in 10 of the 12, and low-performing/degraded/noisy/leaky transistors in every single one, many times more than one. Other Zenith transistor radios from the same era haven't had the same sort of problems, so maybe it's a statistical anomaly, but it's got to be way out there on the bell curve.

With the socketed transistors, maybe the ease of substituting them make me more likely to find weak ones than the more general case, but I have found a much higher failure rate of germanium transistors than I have tubes and astronomically higher failure rate of germanium transistors over silicon. The failure rate is not as high as some brands of electrolytic caps but I would certainly put the transistors in a strong second place.

Brett

Well, I guess this is why one would digest a variety of experiences, to get a compass of sorts.

I've recapped well over 100 Transistor (I've lost count, actually), and hybrid sets.

I especially like and collect the earliest of the genre, so Germanium Transistors have been prevalent.

How many have I replaced? Very few. As an example, out of 10 Regency TR-1 and TR-1G's
a total of three Transistors (donated from my 11th set).

AFA my 13 hybrids (Emerson/Hoffman/Tom Thumb/Firestone) each of which used two of the very earliest Transistors,
I've restored 11, and only one of them required an output Transistor change.

My mid-fifties Philco/Emerson/Admiral/Sonora/Westinghouse/RCA/Motorola/Arvin/Bulova/etc. haven't required
but perhaps three at the most.

I would say that replacing the (usually 4) Electrolytics, adjusting the two or three IF cores to compensate for component age related drift,
as well as the antenna trimmer on the tuning cap, fixes 85% of American and Japanese Transistor sets, given that the earphone jack isn't tweaked.

Touching the solder pads with a hot iron to re-flow the solder is another step to either get a radio working, or working better
if it's performance isn't as good as it should be.

Also to my ear Germanium transistors have a different sound to later ones, this is why im now trying to find some spares for my 2 solid state consoles using Germanium transistors.
Probably somebody will say im wrong about the sound, but to my ears they have a very clean sound, its also nioce to keep them going because in years to come there will be no more germanium transistors.

Bad germanium transistors are a major cause of failure in British built radios of the 60's. Basically, the whole of the AF 11x range suffers from the tin whisker problem. There are equivalents you can use to rectify the problem though. Also look out for the OC range too - they do tend to get a little leaky after some 30 - 40 years of service.

I'm assuming that US built equipment didn't often use British made transistors?

...you would be correct. US manufacturers, initially at least, used the American 2N range of transistors. However, it wasn't long before even US-built radios began sourcing parts outside the US, so you'll find a wide variety of transistors were used--often they were 'house numbered' (such as the Zenith 121-xxx numbers) which disguised their actual origin...the transistors themselves might have been renumbered 2N-types, or Japanese 2SA/2SB/2SC types, or even the occasional European transistor...sometimes--if you were lucky--the service literature would actually cross the 'house numbered' transistor to its 'standard' equivalent (again, Zenith sometimes did this)...
...the OC range of European transistors are indeed very rare in the US, mostly found in very early European imports. Other European ranges (AC, AD, AF, etc.) are not quite as rare, but still primarily limited to imports, and usually come from Germany or the Netherlands rather than the UK (I don't know of a lot of British radios being imported into the US)...

Since arriving in Canada from Britain in 2007, ive done a lot of searching but it seems british radios/consoles/phonographs of any number are few
in Canada/America.
One or two brands slip through sometimes but it looks like they where imported.
Only things to make it in vast quantities where BSR/GARRARD turntables.
Im always on the lookout for a new phonograph if anybody has a british one hidden away let me know.

For what it is worth, I have some Amperex 2N2091 transistors for a Royal; 1000/3000 that seem on even close inspection to be identical in every detail (down to the details of various tool marks in the base) to the equivalent Zenith 121-xxx originals. The only difference I can see is the numbers stamped on the side.

I am not sure any of the failures I have seen were due to tin whiskers but all of them look just like the tin-plated "bad" style and I would expect the problem to be present any time there is exposed tin. So I wouldn't make much of the country of origin, it appeared to be an industry-wide problem.

Brett

... and now that here in the UK (at least), we're bound by law to use lead free solder for anything other than "personal use". It's 99% tin, so are we asking for trouble?

I mention it being a British transistor problem specifically, because it was on the range of transistors made by Mullard, and the problem is probably down to the manufacturing method used for this specific range. If other manufacturers devices suffered from the same problem then that's news to me.

NASA did an investigation.... http://www.vintage-radio.info/whiskers/ Makes for interesting reading

Tin whiskers are a *ubiquitous* problem. I don't know specifically about old germanium transistors used in Zeniths (although they seem to be tinned with, er, tin and appear to be identical to ifnot actually of Mullard manufacture). But I work in the aerospace industry and we still occasionally run afoul of tin migration issues. For example, we have some wire-wrap prototype boards in one of our test labs that develops a short about every six months due to tin whiskers. We take it out, put down some paper, and then drop it, flat from about 18" onto a table. Sometimes you can see them after they fall out. Put it back in, works dandy again for a while.

Unless you have some sort of encapsulation or coating, soldering with pure tin, particularly on SMT parts, will cause you a problem eventually.

Brett

Thanks everyone for the benefit of your experience. I think I'll heat up the pencil-tip, replace caps and and get some of my long-silent pocket radios going again.