What is the fifth transistor likely for?
mm
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
would be silicon. But who knows?)
Arfa Daily
"mm" <NOPSAM...@bigfoot.com> wrote in message
news:oo00l6l3hjbh87osg...@4ax.com...
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
Dave Platt
> 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 <dpl...@radagast.org> 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!
Sjouke Burry
Used to keep the bias where it belongs.
isw
"William Sommerwerck" <grizzle...@comcast.net> 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
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
news:4d508cec$0$8915$703f...@textnews.kpn.nl...
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?
--
Adrian C
Arfa Daily
"Mark Zacharias" <mark_za...@sbcglobal.net> wrote in message
news:4d512809$0$10821$c3e8da3$eb76...@news.astraweb.com...
Ha ! Thanks Mark. I was beginning to think that no one had understood
exactly what I said ... :-)
Arfa
Meat Plow
I knew what you said. There shouldn't be a need to compensate for temps
in something that doesn't put out a lot of wattage in the first place.
--
Live Fast, Die Young and Leave a Pretty Corpse
William Sommerwerck
> something that doesn't put out a lot of wattage in the
> first place.
Not so -- not for germanium transistors, anyway, which were very
temperature-sensitive. Look at the schematic for any early transistor
radio -- there's a diode or thermistor in the output stage.
I was the first to suggest temperature compensation -- but also pointed out
it was unlikely.
Meat Plow
>> There shouldn't be a need to compensate for temps in something that
>> doesn't put out a lot of wattage in the first place.
>
> Not so -- not for germanium transistors,
Grow up Bill. Poster said circa 1998. How many combos from then had Ge
outputs?
Arfa Daily
"William Sommerwerck" <grizzle...@comcast.net> wrote in message
news:iispii$tmi$1...@news.eternal-september.org...
Many modern amps still have temperature compensation for the output
stage(s). However, it's very unusual to see it made from any transistor
package larger than a TO92 in a typical 10 to 60 watt hifi rig. These will
often be clamped to the heatsink on their 'flat' side, with a sizeable
dollop of white heat goop. They may also be encountered pushed into a hole
in the heatsink, or sometimes just pushed or glued against it. Occasionally,
they can be found clamped between the heatsink, and the PCB. You will also
see the same mounting tricks used with glass (1N4148) silicon diodes, and
sometimes with them just sticking up from the board and close to - but not
actually touching - the heatsink. Very occasionally, you will find a tiny
bead thermistor doing the job.
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.
Arfa
William Sommerwerck
>>> something that doesn't put out a lot of wattage in the
>>> first place.
>> Not so -- not for germanium transistors...
> 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
> 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?
Arfa Daily
"William Sommerwerck" <grizzle...@comcast.net> wrote in message
news:iiu459$rem$1...@news.eternal-september.org...
If the transistor was being used for bias compensation, then yes. Most
likely one per channel. In the case of voltage regulator transistors, the
rails are shared between both amps in most common hifi units, so only one
transistor required per regulated rail, no matter how many channels are in
there.
Arfa
mm
wrote:
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.