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Scott Dorsey
 
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randomexpress wrote:
"Scott Dorsey" ...
randomexpress wrote:
I've seen some tube mics(Korby?) with 5703 tube- a small triode.
Some even suggested that this tube could replace AC 701 in KM 54,56 other
neumanns.


It's a nice tube, the 5703. It was in production in the Raytheon plant
in Massachusetts until the late 1980s, and there are a lot of them out
there because they were used in a lot of military equipmnent.

Is this possible?
If so--how is it done?


Well, the plate voltage is in the right ballpark. I think that the

filament
voltage may be different so you may need to replace the zener in the

filament
supply. You will almost certainly need to change the cathode resistor so

that
the tube is biased properly (and I don't recall what grid-cathode voltage

it
wants but the Raytheon Tube Handbook will tell you).

It will sound different than the AC701. I think this is a good thing
personally.


Any schematics floating around..?



Same schematic, same topology. You aren't changing the circuit at all,
just the tube bias point and (maybe) filament voltage.

Be aware that this will devalue a Neumann mike, but just about any change
will.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."