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

In article ,
"William Sommerwerck" wrote:

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

Not uncommon, and a B-E junction has a matching tempco, which a standard
diode does not. RCA used to make (when they made transistors) a special
"diode" which was a B-E junction in a two-wire package, for just that
purpose.

After saying all that, though, my bet is that the fifth device has
something to do with running the CD drive motor.

Isaac

"mm" wrote in message
news
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.

Might be nothing at all to do with the output stage. PSU regulator
transistors are often fixed to the same heatsink as the outputs.

Arfa

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?

The 2SB1020 (PNP) and 2SD1415 (NPN) are complementary pairs of power
transistors... absmax around 100 volts 7 amps. Presumably the "usual
four" that do the current amplification.

The 2SB1370 is a PNP in the same TO-220FP package. It seems to be
spec'ed out as a driver.

I'd lean towards agreeing with the speculation that this is being used
to regulate the output-stage bias voltages or currents somehow - to
provide thermal tracking. This is more commonly done with one or more
diodes in the bias string (one set per channel) but there may have
been some tricky way of doing it with a single thermally-coupled
transistor on the heatsink which was simpler and/or cheaper to
implement.

Maybe (and this is sheer speculation in the fact of an acute lack of
schematic) this one transistor controls two separate idle/bias strings
via a current-mirror arrangement of some sort?

Or, maybe it's just a "Whoops, too hot!" emergency shutoff switch
circuit, to keep the player from going into thermal runaway if the
owner tries to bend metal and break walls by turning the poor beast up
to 11?

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

mm wrote:
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.

On Tue, 08 Feb 2011 01:23:08 +0100, Sjouke Burry
wrote:

mm wrote:
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.

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.

On 08/02/2011 05:18, mm wrote:
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?

--
Adrian C

On Tue, 08 Feb 2011 15:22:30 +0000, Adrian C
wrote:

On 08/02/2011 05:18, mm wrote:
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?

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.

"Sjouke Burry" wrote in message
...
mm wrote:
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.


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

Mark Z.

"Mark Zacharias" wrote in message
eb.com...
"Sjouke Burry" wrote in message
...
mm wrote:
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.


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

Mark Z.

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

Arfa

On Tue, 08 Feb 2011 17:28:49 +0000, Arfa Daily wrote:

"Mark Zacharias" wrote in message
eb.com...
"Sjouke Burry" wrote in message
...
mm wrote:
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.


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

Mark Z.

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.




--
Live Fast, Die Young and Leave a Pretty Corpse

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.