40 WATT CLASS B AMP.

In 2005 I had a job to fix an "energy transducer" produced by James B Lansing in
about 1959. The energy transducer was just a two channel amplifier.

It was originally full of germanium transistors and many were fused.
I refuse to replace germanium transistors with more of the same in any circuit
unless I am bribed into doing so with so much money that I cannot refuse.
If ever there will be a bunch of electronics that won't be missed it will be all the junk
with germanium which lasted on the scene between about 1954 and 1960.
The resistors and capacitors of that era also were often very poor,
making all the gear with germanium devices even less worth collecting.

The first transistors were point contact germanium items with horrific characteristics,
and makers of tubes chuckled about then since they were such poor performers.
But production increased and they weaseled their way into countless small radios
to give us inferior sound quality that the poor could afford and carry around in
their pockets.
The germanium transistors were very prone to easy failure from heat and had
poor linearity and had current leakage and noise problems.
In about 1960, the bipolar junction transistors were made using silicon and
with a new heat process and suddenly it was all over for germanium AND vacuum
tubes because the silicon was thermally much more rugged than the germanium,
and perhaps even better sounding.
The current linearity of the new silicon based bjt wonders was a lot better
and leakage currents were not a problem and soldering them was easy without
having to use heat sinks clipped to the leads while soldering.

The world suddenly got a heck of a lot more cheap electronics, but no better
musicality in amplifiers.

The early JBL "energy transducer" was merely a 30 watt per channel stereo
amp for an organ and speaker console a guy has in Melbourne.

I removed all the germanium based circuitry and old R&C parts and filed them
in the rubbish bin.

The new circuit I used is as follows :-
Fig 6.
Schematic 40watt
          bjt amp.

The circuit uses the original power transformer with CT secondary to produce
+/- 27Vdc rails with a bridge of diodes.

The arrangement of Q7&Q8 as darlington pairs to drive the Q9&Q10 effectively
give the output emitter followers stage a high base input resistance at Q7&Q8
because they are effectively connected as darlington triples. Therefore the gain
of the VAS stage Q4&Q5 is not disturbed by input resistance variations of the
output stage. The amp continues to make nice organ music.
But hey, give me a Hammond with a tube amp if you want the best sound!

Fig 7. 
40w amp on
          bench1
I made the perforated steel cover which slots into position at the
bottom and is firmly held by two screws for easy access for servicing.

Fig 8.
40w amp on
          bench2.
I fitted new RCA inputs and level adjust pots, IEC mains input socket
and fuse holder.

Fig 9.
40w amp on
          bench3
This Fig 9 view is with all the covers off and the amp lying with the panel
face down.
The boards for each channel are white fiberglass with wire tracks and
surface mounted R,C, and other parts. New PS capacitors are fitted
on the right side with a pair of fuses for the outputs in front of the caps.

Fig 10.
40w amp on
          bench4.
With all covers screwed into place. The amplifier unit fits into a long
speaker unit for an organ with speakers at each end.

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