Old Gernanium Transistor Repair

do you remember what years those hybrid car radios were produced?

NT

where in the world does a can of lighter gas or camping gas cost 10 bucks?

NT

Mid 60's? IIRC the tubes used ran OK with just 12 VDC on the plates.

I'm sure there was no vibrator then.

This is just illogical. What is Vce when not oscillating, and whats psu v? Posing the osc cct would give more opportunities for upping or stabilising the gain.

NT

First one I saw was early '60s.

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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW To e-mail, change noise into sound.

Late '50s & early '60s. Most of the hybrid car radios used tubes that operated with +12 VDC on the plates, as well. This eliminated the problem of bad vibrators.

A lot of transistor radios were repaired in the '60s and & '70s. Sams published 159 different TSM manuals, covering about 1000 models. B&K made a piece of test equipment specifically to repair transistor radios, as well. It had a power supply for the radio, a signal generator, signal tracer, and voltmeter all in one package so you could quickly locate and repair the faults. Most of the problems were bad transistors at that time, followed by bad volume controls and variable capacitors.

Yup - and just in time for 'Good Vibrations'...

now i know, thanks everyone.

PS Some were proudly marked 'transistor' on the front panel, one could be forgiven for not realising that meant just the one.

NT

The 1958 Fords had radios with 12 volt tubes and a 2-transistor power amplifier. The transistors were 2N256's or thereabouts. If you looked them up in the GE transistor manual, their high frequency cutoff was like 4Kc ! Not Mhz or GHz, KHz!

Hi...

But for those of us who were able to order them with the incredibly expensive optional radio, they sure sounded good to us :)

Take care.

Ken

AM radio doesnt go that high anyway. There still would have been output above 4kHz, and preemphasis is not so hard.

Worst Ge spec I ever saw was 2kHz ft. Not for audio.

NT

That doesn't sound so great for audio use.

Transistors had to start somewhere. There was a famous article in the amateur radio magazine "QST" where the author said something about how transistors could never amount to much, and included something about their not being able to work at radio frequencies. But it wsa an early article.

IN retrospect, 4KC seems awful low, and even transistors suitable for 455KHz IFs seem low, but at the time each increment must have seemed a big step forward, because it was all so new.

Michael

Lets cut right to the way to fix this . First get the radio apart so you can get to the capacitor connections .

Take a 25mfd at 15 volts or so , get the radio playing and touch that capacitor across each one in the radio . If its bad te radio will improve , replace the capacitor . Another way would be to just replace all the capacitors ... probably 5 of them ? This will eliminate any capacitor issues

If the radio still has the noise when cold . Get it so you can get to the tops of the transistors and when cold & noisey touch a hot soldering iron tip on each transistor top one at a time quickly to warm the part up . If its a transistor this will find it .

Vce is about the same as the battery voltage. I haven't traced it all out but most of the voltage is dropped across the oscillator transistor. As I said, reducing the emitter resistor increased the current and gain about 3dB or more. It now works fairly well outdoors on warm days. But there is still too much internal noise. The noise is not from the antenna, and must be coming from the oscillator or IF stages. I suspect the germanium transistors.

I'll take it apart again Monday and try and figure out the bias scheme for the oscillator.

-Bill

snipped-for-privacy@att.net wrote in news: snipped-for-privacy@h54g2000cwb.googlegroups.com:

I was just thinking are you shure it is the oscillator ?

Tune near the bottom of the band take another radio and try to tune to the oscillator probably 455Kcs above tuned frequency, listen for a dead spot with a little background noise, that changes when the dial is rocked slightly on the defective radio. Do this while the radio works then chill it and see if you can still tune the oscillator or not, don't change the dial on the now cold radio.

I had a problem similar to this and it was a bad IF transformer worked fair when warm got worse as temperature droped and guit completely at aproximately 25 deg. F.

If it worked with gernamium transistors at one time when the defect is repaired it should function without major modifications, which would be necessary with the change to silicon transistors.

Hope you understand what I am saying.

R!

"R!" wrote in news:1164112908.770760 @nnrp1.phx1.gblx.net:

How did you figure out it was the IF transformer? And did you figure what was wrong with the IF transformer? I mean, gee, what could go wrong with an IF transformer that would vary with temperature?

Broken winding I suppose, or worn through insulation causing a shorted turn.

Jim Land wrote in news:Xns9882A71FBADDCRrrrFfffTttt4396hotm@216.168.3.44:

The IF transformer has some really small capacitors in their base, one of the capacitors developed leakage that varied with temperature.

I use an old radio to find problems such as this. Make a removable connection at the detector circuit in a working radio and use it for a signal tracer. The connection contains a .01uf capacitor in series as well as a 100k resistor near the end used for a probe. Connect chassis together for ground return, sometimes the + side of the power supply.

R!