mm wrote:

I just acquired a Lear Sigler brand, Bogen Communications Division, 30
watt, monaural audio amplifier, model 330A Series H-57, with tubes,
that has 3 empty tube sockets. Unlike the other sockets which have the
tube numbers on the chassis next to the sockets, these three don't.

How very coincidental; I just repaired one of these and I will be photographing
it from all angles and will post an url for the results (it is really a beautiful
piece). Fortunately the schematic is easily found on the web but I will also
include it on the site.

I was impressed that after years of operation, it sounds great, has no hum
and very low noise.

Here is a tube placement diagram:

FRONT
------------------------------------------
| |
| V5 |
| V3 V2 |
| |
| V1 |
| V4 |
| X3 X2 X1 |
|-----------------------------------------

v1 6eu7 x1 t-200 input network
v2 6eu7 x2 t-200 input network
v3 7247 x3 t-200 input network
v4 7868
v5 7868

Regards,

Michael