[sdiy] slightly OT: solid state power amp topologies

[Harry Bissell]

You can't necessarily tell a class B from a class AB by inspection. It depends on whether the
bias causes one transistor to cut off before the other conducts (class B) or if there is an area
where they are both conducting.

Class B is actually pretty rare for audio (imho) as it is tough to eliminate or minimize crossover
distortion, which is level independant and really very noticible (and objectionable !)

A Silicon transistor will have a base-emitter voltage drop of around 0.7V, germanium will have a drop
of about 0.2V. That is the best test imho, easier to do out of circuit though...

Transformer coupled power amplifier designs are common in PA amplifiers as you can match impedances
very easily. They usually lack some low-end unless the transformers are very large and heavy...

H^) harry


----- Original Message -----
From: aankrom <aankrom at bluemarble.net>
To: synth-diy at dropmix.xs4all.nl
Sent: Sat, 12 Nov 2011 15:07:19 -0500 (EST)
Subject: [sdiy] slightly OT: solid state power amp topologies

I am removing an amplifier from an old Kimball 600 organ. The power 
transistors are unmarked, but in the schematic, they have the same 
(Kimball) part number. Both are PNP with a bipolar supply. Is this a 
class B amp or a class AB amp? If it's a class B would it be possible to 
bias it to class AB? It does have a transformer before the power stage. 
Is there a good test to see if a power transistor is Ge or Si? About how 
much power could you expect from two T03 sized power transistors from 
the mid-70's? The power supply for this thing is a monster - it uses 
four inductors.

I have a speaker cabinet that is perfect for this - it's big so the 
reverb tank will fit easily. It's about 3 feet tall and about 2 feet 
wide.

The organ itself is yielding up two nice manuals, a pedal, a swell 
pedal, lots of wire and nice Ge transistors and Orange Drop caps.

Anthony
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-- 
Harry Bissell & Nora Abdullah 4eva