[sdiy] Diode voltage drop

[Fredrik Carlqvist]

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...
> 
> -- 
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