Old Gernanium Transistor Repair

[[email protected]]

Maybe you have a suggestion to overcome the temperature problems?

As already suggested and explained, find the fault. Anything else is
just senseless.


NT

 

[Michael A. Terrell]

It's just a little pocket size radio (5 X 3 X 1.5) with 2 sections for
the tuning cap.It has the usual four RF coils and input and output
audio transformers. But that only requires 6 transistors, and there are
8 used. I suppose I can trace out the connections to try and figure out
what the extra 2 transistors do.

Does your radio have a brand name and model number?


--
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

 

[Ancient_Hacker]

It's just a little pocket size radio (5 X 3 X 1.5) with 2 sections for
the tuning cap.It has the usual four RF coils and input and output
audio transformers. But that only requires 6 transistors, and there are
8 used. I suppose I can trace out the connections to try and figure out
what the extra 2 transistors do.

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.

 

[James Sweet]

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.

 

[[email protected]]

Does your radio have a brand name and model number?

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

 

[[email protected]]

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. 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

 

[Homer J Simpson]

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.

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.

 

[[email protected]]

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:

http://www.ccrane.com/radios/am-fm-radios/ccradio-plus/index.aspx

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

 

[Homer J Simpson]

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:

http://www.ccrane.com/radios/am-fm-radios/ccradio-plus/index.aspx

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.

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

 

[Jim Land]

[email protected] wrote in @e3g2000cwe.googlegroups.com:

The radio I'd really like to have is the CCRadio Plus
from ccrane company, for $134 at:

http://www.ccrane.com/radios/am-fm-radios/ccradio-plus/index.aspx

It's supposed to be optimized for 'talk radio' and voice frequencies...

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

 

[Michael A. Terrell]

[email protected] wrote in @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:
but be ready for the flaming idiots who like to
hijack almost every thread.


--
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

 

[[email protected]]

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

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

 

[[email protected]]

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

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

 

[Michael A. Terrell]

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.


--
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

 

[Homer J Simpson]

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

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.

 

[David Nebenzahl]

Michael A. Terrell spake thus:

Some of them think that Atwater Kent radios are too new for that
group. Ignore them, there are a number of transistor radio collectors
in that group. I have most of the "Sams Transistor Radio Manuals" in my
collection: http://home.earthlink.net/~mike.terrell/HWSTm.html The Sams
index is available online.

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?


--
Just as McDonald's is where you go when you're hungry but don't really
care about the quality of your food, Wikipedia is where you go when
you're curious but don't really care about the quality of your knowledge.

- Matthew White's WikiWatch (http://users.erols.com/mwhite28/wikiwoo.htm)

 

[Michael Black]

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

 

[[email protected]]

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

 

[Homer J Simpson]

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?

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.

 

[Homer J Simpson]

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.