Old Gernanium Transistor Repair

Does your radio have a brand name and model number?

They often used transistors that were weak or had one dead junction as diodes-- either as detector and agc diodes, or as biasing diodes for the output stage.

Sounds like a perfect job for a can of freeze spray. Warm it up until the problem goes away, then give suspect components a quick shot of cold.

Yes, it's a "Keytone" or "Kaytone" deluxe model, 8 transistor, made in Japan. Chrome faceplate, white plastic body, red plastic back. I searched Google but didn't find much.

-Bill

Yes, good idea, but the can of freeze spray costs $10, and the radio only cost two dollars. So I put the radio in the freezer for 30 minutes and took it out and it didn't work at all. Then I applied a hot sodering iron to the body of the oscillator transistor and it very quickly started working again. Seems the oscillator doesn't run at low temperature.

Would you guess the solution is a silicon transistor? or just adjust the bias on the existing germanium transistor?

-Bill

Might be a collectible. If so, don't screw with it. Sell it to a fool^H^H^H^Hcollector and use the money to buy a good set.

Yes, I'm thinking about selling it, but I want it to work well, as good as new or better. The radio I'd really like to have is the CCRadio Plus from ccrane company, for $134 at:

It's supposed to be optimized for 'talk radio' and voice frequencies, but it's a little large to carry around. Runs on four 'D' cells for 250 hours and has a leather case and a bunch of options, solar charger, Antenna amplifier, ect. It's supposed to be one of the best AM radios. I see it on ebay all the time, so I might make a bid and get it for $100 or less.

-Bill

I somewhat covet a Grundig all wave hand cranked, but I expect it's made in China too.

snipped-for-privacy@att.net wrote in news:1163559828.809638.315730 @e3g2000cwe.googlegroups.com:

I wonder how that is different from "lacks good bass and treble"?

Some of those CC Crane radios have a high failure rate on the LCD displays. Ask about the model you are looking at on: news:rec.radio.shortwave but be ready for the flaming idiots who like to hijack almost every thread.

neither, increase the stage gain. That probably means higher collector R or similar. You may then need to adj the bias a little.

Or with an old radio like that it might just be biased way wrong, where gain is down. Meter it and see where Vce sits when not oscillating.

NT

neither, increase the stage gain. That probably means higher collector R or similar. You may then need to adj the bias a little.

Or with an old radio like that it might just be biased way wrong, where gain is down. Meter it and see where Vce sits when not oscillating.

NT

PS keep slobbering irons off geraniums, they max out at 90C, and slobber doesnt even melt till over 200. Just soldering Ge trs into pcbs is prone to killing them, this is why they typically had long sleeved leads.

NT

Some of the early, cheap transistor radios used really poor quality transistors. they had so much leakage that they were self biasing. Even if you replace them with a good germanium transistor, they may need the bias adjusted.

I did have one set only (ever) that had weak transistors. It was a minimum count model (5 or 6) and I replaced all of them to get it to work again.

Michael A. Terrell spake thus:

Which implies that, at least sometime in the past, there were those who repaired those radios. Did they? I remember when those things appeared on the market, and I always thought of them as disposable items. Did people actually take them in to be fixed?

Who knows. But early transistor radios, that would have used germanium because there was no choice, were not cheap radios. They cost significant amounts at the time. Even later, one could still get decent transistor portables that would have cost a fair amount at the time. I once found a Sony portable from the early sixties, and it has metal casing and is quite heavy, complete with the large speaker. People would have been having those repaired, there's no way they'd toss them if they stopped working.

The cheap transistor portables came later. Likely they were less likely to be repaired, but circuit wise they weren't that different from the expensive portables.

Michael

The collector appears to drive the oscillator coil and mixer coil in series (no collector R other than maybe decoupling). There is a emitter resistor of 2K with a drop of 0.35 volts. I figure the oscillator stage is running at 0.35/2000 = 175 miroamps. I added a 3K resistor in parallel with the 2K so the current is increased to 0.35/1200 = 292 microamps. This brings up the gain about 3dB, but the radio still fails at low temperature in the refrigerator. At low temperature there is only noise and no signal. I tried this with a more modern radio using silicon transistors and it works well an 40 degrees or so. So, I'm almost convinced the problem is the germanium transistors.

Will continue to investigate.

-Bill

The first Sony shirt pocket (just) sized one cost me more than a week's wages - at wholesale! I repaired them for a few years until I moved on to other things.

We had a popular Philips model that had a transistor audio output stage (OC71s and OC72s) but still had tubes for the convertor and IF. Later they came out with the OC44 and OC45 and went fully solid state.