What is the fifth transistor likely for?

[mm]

I was junking a moderately priced combo CD, AM/FM/Casette, from 1998,
that I got out of the trash and which wouldn't play CDs anymore, and
it had an array of five output trnasisttors, instead of the usual
four. All are the same size, on one big heat sink. No schematic
of course.

The part numbers are obscured but I can see the ends of several.
1 B1370
2 B1020
3 B1415 (or 01415, or D1415, or ?1415
4 B1020 same as 2
5 same as 3

What is the fifth transistor likely for?

Don't put a lot of work in to this. The device is junked/trashed
already.

 

[William Sommerwerck]

Temperature compensation for the bias? (This seems unlikely, as the devices
would be silicon. But who knows?)

 

[Sjouke Burry]

I was junking a moderately priced combo CD, AM/FM/Casette, from 1998,
that I got out of the trash and which wouldn't play CDs anymore, and
it had an array of five output trnasisttors, instead of the usual
four. All are the same size, on one big heat sink. No schematic
of course.

The part numbers are obscured but I can see the ends of several.
1 B1370
2 B1020
3 B1415 (or 01415, or D1415, or ?1415
4 B1020 same as 2
5 same as 3

What is the fifth transistor likely for?

Don't put a lot of work in to this. The device is junked/trashed
already.

Temperature measurement.
Used to keep the bias where it belongs.

 

[mm]

Temperature measurement.
Used to keep the bias where it belongs.

Thanks all. Very interesting ideas. Maybe it wasn't as cheap as I
thought it was. But I had no use for it. I just like to look at
things and fix them when I can.

 

[Mark Zacharias]

Temperature measurement.
Used to keep the bias where it belongs.

Doubtful. As Arfa mentioned, probably a regulator (voltage, not temp). Quite
common to mount on the same heatsink as the output transistors.

Mark Z.

 

[Adrian C]

Thanks all. Very interesting ideas. Maybe it wasn't as cheap as I
thought it was. But I had no use for it. I just like to look at
things and fix them when I can.

There is an dramatic element of keeping us in suspense here

Could you give a clue to the make / model for some of the clever peeps
to find a schematic on this?

 

[Meat Plow]

Ha ! Thanks Mark. I was beginning to think that no one had understood
exactly what I said ...

Arfa

I knew what you said. There shouldn't be a need to compensate for temps
in something that doesn't put out a lot of wattage in the first place.

 

[William Sommerwerck]

There shouldn't be a need to compensate for temps in

something that doesn't put out a lot of wattage in the
first place.

Not so -- not for germanium transistors, anyway, which were very
temperature-sensitive. Look at the schematic for any early transistor
radio -- there's a diode or thermistor in the output stage.

I was the first to suggest temperature compensation -- but also pointed out
it was unlikely.

 

[Meat Plow]

Not so -- not for germanium transistors,

Grow up Bill. Poster said circa 1998. How many combos from then had Ge
outputs?

 

[William Sommerwerck]

There shouldn't be a need to compensate for temps in

Grow up Bill. Poster said circa 1998. How many combos
from then had Ge outputs?

None. But that isn't what you said.

 

[William Sommerwerck]

I have only seen flatpack transistors being used for this purpose where

we're talking big power levels, such as in PA amps.

However, repairing this Chinese crap every day of my working life, I can say
that it is extremely common to find one or more flatpack devices, additional
to those being used for the output stage, mounted on the same heatsink. I
guess this is to cut down on cost. Invariably, these 'extra' devices, are
simple linear voltage regulator pass transistors, and that is what I would
be fairly sure that the OP's fifth transistor would be.

There's also the fact that there's only one extra transistor. Wouldn't a
two-channel output stage require two?

 

[mm]

There is an dramatic element of keeping us in suspense here

Could you give a clue to the make / model for some of the clever peeps
to find a schematic on this?

Sorry. I stopped reading the thread. By the time I first posted, I
had destroyed it. Don't remember the brand, much less the model.