12AY7 or 12AU7 as V1 in a Fender Bassman preamp?

[dehughes]

Specifically, in a Black or Brownface Bassman preamp.....would either of those tubes have enough oomph to drive the tone controls in an effective fashion? I'd like to try something like that in my next amp....low power/gain bassman-ish...

[Andy Le Blanc]

12ay7 should do it, the 12au7 wont give the gain you might expect, that style
of tone stack has a -10 loss. 12ay7 has a max design center plate voltage
of 300 a little less that the 12ax7 330, but its max plat dissipation is larger than
the 12ax7 1.2w per unit, at 1.5w per unit. Its amplifaction factor puts it
between a 6sn7 and 6sl7.

[David Root]

Harp players use both in their amps, which are often old tweed Bassmen or clones thereof. Fattens up their tone and cuts acoustic feedback.

However a harmonica is not a guitar pickup. I think Andy is right, the Y works but the U likely would not.

[ER]

why not try an octal build?

[David Root]

I've done a fair amount of work with 6SL7/6SN7 preamps and they do have nice tone, BUT if you are using stage gain levels much above 30 or so (which is what we are talking about here) you will have to use a 6V DC heater supply on all of them or they will hum like crazy.

I have even done a Dumble OD stage with them and with DC heaters they hum pretty hard when you crank them >50W or so on a 100W amp. In my experience they are better on cleans than OD, and certainly easier to control.

[dehughes]

Very cool...thanks guys. I actually WAS considering a 6SL7 Bassman build, but put that off in favor of nine pins mostly because of the extra heater hassle (had to build a DC supply for my 6SN7 amp...). Plus, I've kinda fallen for the 12AY and AU7 tubes as of late, so I was toying with the idea of a low-gain Bassman-ish thing.

So, the AU7 won't work at all in your typical Black/Brownface Bassman V1 spot? Or, are you saying it will do it, but with the tone stack it will be basically unusable in terms of gain?

[M Fowler]

DeHughes,

I built the Bassman 5b6 PTP using 6SL7, 6SC7, 6L6 pair and 5U4 rectifier. Its a two knob job but is a nice sounding amp but yeah it doesn't get very loud but has a sweet breakup and deeper tone. Easy to build as well.

Mark


https://tubeamparchive.com/viewtopic.ph ... highlight=

[Andy Le Blanc]

6FQ7/6CG7 can be used as a 9-pin for 6SN7.
6AT6 is a 7-pin (one stage) on the same RC table as a 6SL7.

the voltage gain of a 12au7 is low, pop a couple in an amp in place of a
12ax7 and you'll hear immediately. I really like they're tone too,
but the voltage gain is really low for the application. You'll have to modify
your intended gain structure after the pre to bring the over all signal up post
to get the power side of the amp to respond in a expected manner.
Not bad, just plan ahead for it.

[dehughes]

Very cool...thanks! I think I may have a 6AT6 on hand, actually...

I'm trying to stick with one V1 tube (input and post tone stack triodes) and one for the PI (probably LTPI....maybe paraphase...). We'll see...

[Structo]

Yeah the gain on the 12au7 is what? 17-20?


I have an amp that I was experimenting with. It would oscillate if I turned the volume up too high.

I ended up with a 12au7 in the phase inverter (LTP).
I didn't have any 12at7 or 12ay7 around so the au7 was all I could try.
That really calmed it down and sounded pretty darn good.