Dual bandmaster design- plausible?

[reverendbk]

I have a defunct bassman 10 that I am converting to 5E7. However, given the huge chassis and tons of knobs, I would like to give each channel of the original 5e7 its own cathode-followed tone stack (yes i realize I need to add a tube. from what i read, this is not a problem for the PT).
So each half of V1 would go to its own volume (like normal) and from there each to its own direct-coupled CF stage (V2&3 respectively), followed by the tone stack. They would then mix into the last stage (V4).
I think this will be a really cool amp, but am not sure about mixing both tonestacks back into the last tube. I don't want the tone controls on one channel to affect the other channel. Would putting a couple of 470K mixing resistors into the final grid be sufficient? Or is this just a bad idea...

[Don Moose]

Well, 2 volume controls (1M?), each with a 470k from the wiper to a common node (grid) would, worst case, be like another volume control at 50%.

Worst case being one volume control at zero.

It's not quite isolation, but better than nothing. If you're not going to be using the two channels simultaneously, a couple of series LDRs to select one or the other might be a better choice.

Hope this helps!

[Bruce / Mission Amps]

I have a defunct bassman 10 that I am converting to 5E7. However, given the huge chassis and tons of knobs, I would like to give each channel of the original 5e7 its own cathode-followed tone stack (yes i realize I need to add a tube. from what i read, this is not a problem for the PT).
So each half of V1 would go to its own volume (like normal) and from there each to its own direct-coupled CF stage (V2&3 respectively), followed by the tone stack. They would then mix into the last stage (V4).
I think this will be a really cool amp, but am not sure about mixing both tonestacks back into the last tube. I don't want the tone controls on one channel to affect the other channel. Would putting a couple of 470K mixing resistors into the final grid be sufficient? Or is this just a bad idea...

How many preamp tubes can you stand to have on the chassis?
There is a very easy way to mix two channels into a single 12AX7 sharing a common anode or cathode....
*********
added:
This will give you something crazy like 10Meg ohms of isolation...

[Chris / CMW amps]

If I understand correctly it's like this:

half tube - volume - whole tube - tonestack - to PI
and
half tube - volume - whole tube - tonestack - to PI

You could at least try using two mixing-resistors (220k to 470k) coming from the tonestacks to the PI-driver-input-grid.

Compared to the stock circuit the PI will (probably) driven somewhat "softer" but that cab be a +, depending on your sound-wishes. If it's too much you could (then) try lowering the amount of neg. feedback if needed to up the gain from the PI.

Hope this helps!

[drewl]

How about each tonestack going into the different inputs of the phase inverter?
Some amps use the 2nd PI input for the reverb signal.

[Bruce / Mission Amps]

How about each tonestack going into the different inputs of the phase inverter?
Some amps use the 2nd PI input for the reverb signal.

These amps use a cathodyne driver/splitter... not a long tail pair.

Can you see yourself clear to insert two more sockets?
There are only three now but the chassis is huge....
Another 9 pin socket and maybe a 7 pin for a 6C4 or even two 9 pins for a 12AX7 using only one half?
The anode mixer is your answer.... the channel isolation is incredibly high.
You'd use the extra, fourth socket as the single triode cathodyne driver.

I drew this from memory (times two channels) so don't count on it being 100% accurate!!
Main thing is to look at the anode mixing stage before the phase inverter
triode.