[sdiy] Diode voltage drop

[Harry Bissell Jr]

The diodes are usually attached to the heatsink and
form a part of temperature controlled biasing. You
could try a generic (iN400x) but sometimes these are
special components and using the wrong one can cause
thermal runaway.

If they are NOT on the heatsink, I'd try the generics.

If they are, I'd try to find exact matches

H^) harry

--- Fredrik Carlqvist <Fredrik.Carlqvist at iar.se>
wrote:

> 
> I suppose Q5 and Q6 are power transistors like
> 2N3055? 
> 
> Probably D2 and D3 are used directly as a voltage
> source for biasing the
> output transistors.
> 
> I think you'll be ok with 1N400x. The difference in
> forward voltage at
> currents between 100 and 200 mA is not so big. Since
> 1N400x will have a
> lower drop than the specified diode, there should
> not be a risk of
> thermal feedback. 
> 
> However, crossover distorsion at lower currents
> could be slightly
> bigger. But since they are not mounted on the power
> trannies (it seems),
> I don't think they are  critical.
> 
> Without the values of resistors, transistor types
> and voltages, it is
> hard to say exactly what is going to happen. I guess
> you'll just have to
> try it. Or fry it? :-)
> 
> 
> Fredrik C
> 
> > -----Original Message-----
> > From: owner-synth-diy at dropmix.xs4all.nl 
> > [mailto:owner-synth-diy at dropmix.xs4all.nl] On
> Behalf Of Tom Arnold
> > Sent: den 27 juli 2005 10:36
> > To: synth-diy at dropmix.xs4all.nl
> > Subject: [sdiy] Diode voltage drop
> > 
> > So, I'm trying to identify a diode to replace it.
> > 
> > First off, the schematic :
> >
>
http://home.insightbb.com/~dunn.greg/ST120/schem2.jpg
> > 
> > Between Q3 and Q4 you'll see D2/D3 in series. 
> They are specified
> > as .8 volt drop at 140ma.  In another schematic,
> the same 
> > part number is
> > specified at .8 volt drop at 100ma.
> > 
> > I'm wondering if I can get away with with a
> 1N400x, which has 
> > .8volt drop at
> > more like 200ma.  I could just leave these diodes
> in, but 
> > they'd be the only
> > silicon I left stock in the whole unit, not that
> that is a 
> > bad thing.  
> > 
> > I just dont grok single ended amps, it'd help if I
> could 
> > locate my service
> > manual which has a detailed circuit description in
> it...
> > 
> > -- 
> > 
>
-----------------------------------------------------------------
> >  - Tom Arnold       -  Free Synth DIY webspace
> http://www.sdiy.org 
> >  - SynthGeek        -
> >  - BBD Fanatic      -  "...is it a virus, a drug,
> or a religion?" 
> >  - echo evho wjxo   -    Juanita Shrugs. "What's
> the difference?" 
> >  --------------------  
> > 
> > 
> 
>