10k
  + ——–/\/\/\/\———
 9v battery                 |
                           —
                            ^
                            |
  – ————————-

That will  drive about 1 mA through the  diode (actually a  tad less).
Then put a voltmeter across the diode.  It will read the Zener voltage
(if  under  9V).   With the diode backward,  it will read  the forward
voltage, which is 0.6 V for silicon and 0.3 V for germanium.

Or you  could trace the  circuit.   Is  this an amplifier stage with 2
diodes and 2 power transistors?   If  so,  the diodes  are part of the
bias voltage circuit,  and are forward  biased to produce a  0.6  volt
drop per diode.  I’d try ordinary  1N914 or 1N4148  diodes in place of
them…  probably close enough.

–
Michael A. Covington                http://www.ai.uga.edu/faculty/covington/
Artificial Intelligence Center                                           <><
The University of Georgia                Unless specifically indicated, I am
Athens, GA 30602-7415 U.S.A.                not speaking for the University.

>I’m trying to rebuild the amplifier stage of a Pioneer bookshelf stereo
>which blew nearly every component in the Right channel (except for the
>electrolytics… went as far as to blow the preamp transistor too).  
>Anyhow, there are two tiny diodes, smaller than the typical small-signal
>diode you get at Radio Shack, I think they are only 3mm long.  I’m not
>sure what kind of diodes they are, one has a black stripe and some
>illegible writing and the other has a blue stripe.  Do the stripe colors
>mean anything or do I have to derive some other method to figuring out
>what they are?  How would I go about figuring out what they are anyway,
>resistance?  diode check mode on a DMM?  Derive a zener regulating
>circuit?  Check voltage drop?
>–
>Shawn Lin "Knock softly, but firmly.  I like soft, firm knockers."
>srl9…@nic.smsu.edu 1-417-883-2169 >sli…@mail.orion.org

ao…@detroit.freenet.org

If this amplifier has discrete output transistors and the diodes are
mounted on their heat sink, they are probably there to maintain a constant
voltage between the output transistor bases and thus cut crossover
distortion.  These are plain old Si diodes, though there may be several
connected in series inside one case.  This gives a higher forward-bias
voltage drop.  You’ll probably need a schematic, but if I were desperate
I’d replace them with small-signal Si diodes and then check for crossover
distortion.  If this isn’t your amp, be sure to solder an
appropriately-sized fuse in series with each speaker line so the customer
doesn’t wreck it again by short-circuiting the speaker lines.
  Your signature quote isn’t as funny as you think it is, and it’s
offensive to some people.  
                                   M Kinsler