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.

I would like to give this amp away, and I think I first need to insert
new tubes, but I don't know what to use.

The other 5 sockets are marked
V1 6EU7
V2 6EU7
V3 7247
V4 7868
V5 7868

Since there is only one speaker output, the 2 pairs of matching tubes
seems to me to indicate push-pull stages to the amp. Yes?

The other three sockets are labled X1, X2, and X3. I've never seen
such names before. Perhaps this is a secret government amplifier?

The sockets are labeled Mic, Tape 1, and Tape 2. Each has a slide
switch for Hi or Lo Impedance, on top of the open backed chassis.

Is it possible that a tube is needed for Lo impedance inputs and not
needed for Hi impedance? Or is it vice versa?

I would like to be able to tell the next owner, if I can find someone
who wants this, what tube he should use if he has the other impedance
input. Does anyone want to wager a guess? The tube sockets are 9-pin
and each has clips for a tube shield. Do they still sell tube
shields? I have some, but I don't know if I can find them.

Four of the tubes are the original Bogen tubes, and the other, V3, the
7247, is a Telefunken tube labeled "Made in West Germany". So I guess
this was repaired between 1945 and 1990. Can anyone suggest when it
was made?

It also has little adjusting holes in the chassis for WMT-1 input and
output, plus an RCA jack labeled "WMT-1 HIZ". Is that the same as
High Z, and what would that be?

Any help is much appreciated.


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