"Homer J Simpson" ) writes:
"Michael Black" wrote in message
...

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.

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.

There was that whole period where transistors were available commercially,
but not very good. I can't say I've heard of hybrid portables before,
but of course car radios that used tubes but a transistor audio amplifier
were quite common.

And I seem to recall that some of the Motorola "lunchbox" style transceivers
used some transistors in the IF stages along with the subminiature tubes
that provided the active elements at higher frequencies.

Michael

Michael Black wrote:

There was that whole period where transistors were available commercially,
but not very good. I can't say I've heard of hybrid portables before,
but of course car radios that used tubes but a transistor audio amplifier
were quite common.

And I seem to recall that some of the Motorola "lunchbox" style transceivers
used some transistors in the IF stages along with the subminiature tubes
that provided the active elements at higher frequencies.

Michael

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

NT

wrote:
James Sweet wrote:
wrote:
wrote:

I have an old 8 gernamium transistor, protable AM radio that is noisy
on weak stations when cold. It works reasonably well when set it in the
sunshine and warms up. The problem seems to be the RF section since the
noise goes away when the volume is turned down. I'm suspecting the
germanium transistors may be the problem and wondering which one might
be replaced with a silicon variety to cure the temperature problems?

I'm not sure what all 8 transistors do. Two are in the output stage,
and another is used as a audio driver that drives the audio input
transformer.There are four RF coils, the usual oscillator (red) and
mixer (yellow) and white (1st IF) and (black (second IF). But that only
requires 6 transistors, and there are eight total. The detector is a
diode, so they didn't use a transistor for that. I haven't figured out
what the other 2 transistors do.

I'm thinking of replacing the oscillator transistor with a high gain
silicon variety to try and eliminate the temperature problems?

Any other ideas?

-Bill



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, good idea, but the can of freeze spray costs $10, and the radio
only cost two dollars.

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


NT

wrote in message
oups.com...
Michael Black wrote:

There was that whole period where transistors were available
commercially,
but not very good. I can't say I've heard of hybrid portables before,
but of course car radios that used tubes but a transistor audio amplifier
were quite common.

And I seem to recall that some of the Motorola "lunchbox" style
transceivers
used some transistors in the IF stages along with the subminiature tubes
that provided the active elements at higher frequencies.

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

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

I'm sure there was no vibrator then.

wrote:
wrote:
wrote:

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

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.

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

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

In article .com,
wrote:
do you remember what years those hybrid car radios were produced?

First one I saw was early '60s.

--
*If PROGRESS is for advancement, what does that make CONGRESS mean?

Dave Plowman London SW
To e-mail, change noise into sound.

wrote:

Michael Black wrote:

There was that whole period where transistors were available commercially,
but not very good. I can't say I've heard of hybrid portables before,
but of course car radios that used tubes but a transistor audio amplifier
were quite common.

And I seem to recall that some of the Motorola "lunchbox" style transceivers
used some transistors in the IF stages along with the subminiature tubes
that provided the active elements at higher frequencies.

Michael

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

NT

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.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Michael Black wrote:

David Nebenzahl ) writes:

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.


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.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

In article ,
Michael A. Terrell wrote:
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.

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

--
*Sometimes I wake up grumpy; Other times I let him sleep.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
Michael A. Terrell wrote:

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.

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!

Ancient_Hacker wrote:
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

Ken Weitzel wrote:
Ancient_Hacker wrote:

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

"Ancient_Hacker" ) writes:
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!


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 .

wrote:
wrote:
wrote:
wrote:

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

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.

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

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

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

wrote in
oups.com:

I have an old 8 gernamium transistor, protable AM radio that is noisy
on weak stations when cold. It works reasonably well when set it in
the sunshine and warms up. The problem seems to be the RF section
since the noise goes away when the volume is turned down. I'm
suspecting the germanium transistors may be the problem and wondering
which one might be replaced with a silicon variety to cure the
temperature problems?

I'm not sure what all 8 transistors do. Two are in the output stage,
and another is used as a audio driver that drives the audio input
transformer.There are four RF coils, the usual oscillator (red) and
mixer (yellow) and white (1st IF) and (black (second IF). But that
only requires 6 transistors, and there are eight total. The detector
is a diode, so they didn't use a transistor for that. I haven't
figured out what the other 2 transistors do.

I'm thinking of replacing the oscillator transistor with a high gain
silicon variety to try and eliminate the temperature problems?

Any other ideas?

-Bill



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:

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.

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?

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


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.


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
. 3.44:

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

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.

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?

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!

R! wrote:


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.


Yes, did that and the oscillator definetly stops at low temperature.
Measured HFE was 75 so I switched the oscillator transistor with
another germanium with HFE of 220. Performance improved, but oscillator
still stops at 40 degrees F or lower. I also switched the last IF with
a high gain silicon and adjusted the bias and retuned the coils.
Performance again improved, but radio still has noise problems on weak
stations. The signal trimmer capacitor peaks near the center of the
range, so I'm pretty sure the front end is aligned correctly. The noise
must be coming from one of the IF stages.

If I can fix the noise problem, the thing should work as good as new at
moderate temperatures.

-Bill

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!

wrote in message
ups.com...

Yes, did that and the oscillator definetly stops at low temperature.
Measured HFE was 75 so I switched the oscillator transistor with
another germanium with HFE of 220. Performance improved, but oscillator
still stops at 40 degrees F or lower. I also switched the last IF with
a high gain silicon and adjusted the bias and retuned the coils.
Performance again improved, but radio still has noise problems on weak
stations. The signal trimmer capacitor peaks near the center of the
range, so I'm pretty sure the front end is aligned correctly. The noise
must be coming from one of the IF stages.

Check the voltages on the bases of the first one or two transistors at
different temperatures. Check all of the resistors - if you have a low
voltage meter that can test without turning the junctions on use it.

wrote:
R! wrote:

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.

Yes, did that and the oscillator definetly stops at low temperature.
Measured HFE was 75

then your problem certainly isnt the transistor.


NT