"NGS" wrote in message
...
Phil S wrote:
"NGS" wrote in message
...

My guitar combo has five preamp tubes. They are all supposed to be
12AX7. For the effects send and return I use a 12AT7. For the first
preamp tube V1 I use a 5751. The last position V5 is the phase
splitter. What happens if I were to use a 5751 or 12AT7 or even 12AU7
in this position? Is it just the last boost stage prior to the power
tubes? Thanks.


In simple terms, the phase splitter of phase inverter (PI) divides the
signal so that half goes to each power tube in a push-pull design. (If
you've got 4 or 6 or 8 power tubes, there is a pair or group on each
side
that acts as "one section".) I don't think it makes sense to use
something
other than what's specified. For the other pre-amp tubes, use whatever
12A?7 tubes that give a sound you like. 7025 and 5751 are variants of
the
12A?7 family. I think using another PI tube will give you signal loss
at
the wrong place in the circuit.


Makes sense, thanks. Follow up question. Telefunken, Mullard, Amperex,
etc. obviously can be useful in "preamp" locations BUT for the phase
splitter does the TONAL QUALITY of the tube still matter. I'm guessing
it still does since it amplifies the signal going to the two power tubes
in PP but maybe not as much as say V1 or V2. Thanks.

I've been told you can put a microphonic tube in this spot and generally it
won't be a problem. I'd put a decent tube in there, but wouldn't waste a
Tele or Mullard. The tone gets made before the PI.