"mm" wrote in message
...
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?

snip

The 'X' sockets are most likely for microphone transformers.
It was common in those days to supply plug-in transformers
with 8 pin octal bases that looked exactly like octal tube
sockets.

Dave