Shared Tone Stack

[C Moore]

I understand what you are saying. Kind of seems like the long way home. I am dealing with an old friend who has some real quirky, idiosyncratic behavior. I am sort of caught in the middle of this. I understand why it seems there are better solutuons......because there are.
I probably just need to start putting my foot down with this cranky, old guy, and have him start listening to some of you guys that have a lot of experience with this stuff. You cannot believe how long it has taken me to get him to this point.
Anyway.....he has just thrown me another curve, and I am going to have to rethink this whole thing. Now he wants high-gain low mids instead of higher-gain and fatter mids. This is a long story that involves a very old friendship with a miserable lout.....
I am going to get back to this after I get ALL his ideas straightened out.
Thank You So Much

[Firestorm]

I posted a new drawing above.
Maybe I will raise that 150 to 220.
This is just a partial drawing. Not complete at all. I was just wondering if the amp will work as I had it laid out.
The owner wants me to make the Deep Switch into a bright switch. He wanted two separate channels, and make them a High and Low input separately for different guitars. Will it be a big deal if the inputs are not parallel.? I guess what I am asking is, is it better to make the cat and plate variations switchable, than it is to just just have to change from one input jack to another.?
He also did not want to add any holes, pots or switches. I was just trying to give him two different/separate channels he could plug into on the bass channel that he never used anyway.
His amp still has the Normal channel also. I am sure I will have to make some changes for him, but I first wanted to make sure the amp will at least work the way I have it wired. Then I know I have a working amp I can do something with per my friends desires.
I really appreciate all the help and suggestions from everybody. I do not play guitar, so I Really Do Appreciate the input. Feel free to make any other suggestions you feel would help.
Thank You

If those two inputs were completely separate (like on a switch) you would hear almost zero difference between the 350pF/56K and the 250pF/33K. As it is, they still interact (with just 89K between the inputs) so the difference will be even less. No point whatsoever.

Both channels have hi/lo inputs stock, so IMO it's better leave the conventional setup to accomodate different guitars and make the tone shaping all switchable. If you replace both volume pots with the 1M switched types and put the bright switch cap there, that frees up both of the slide switches to do other things (switchable slope, switchable cathode bypass, etc.) If you take care to keep the channels in phase, you friend will also be able to bridge them and dial in a sound with the volume pots (technically it would be better to decouple the two channels power supplies to do this, but it does work without that complication). The extra triode gives you all sorts of creative options: you could make one channel stupidly high gain by cascading another triode, though you'll have significant work to clean up the lead dress if you go that route. Or you could do the "Dave Funk" mod and wire a cathode follower between V1a and V1b and put the tone recovery stage on V2.

[C Moore]

Yeah, I was just talking to him about using a cat follower. And trying to figure the best option for that un-used triode.
Thanks for the input info. That will by all I need to convince him to try something different. Let me find out exactly what he wants this time around, so I do not need to keep bothering you guys with a bunch of "what if" scenarios.
I really need to know what he needs from the "bass channel" that he is not getting from the "normal" channel. Let me see if I can get Steve to cough up some specifics, so we can all put this one behind us. Glad he does not read these forums. I guess that is what he has me for.
And yeah, I really like your efficient use of the deep and bright switch. And I will get him back into the typical input jack set-up.
I really appreciate everybody's effort and suggestions.
Thank You Very Much

[C Moore]

I posted a new drawing above.
Maybe I will raise that 150 to 220.
This is just a partial drawing. Not complete at all. I was just wondering if the amp will work as I had it laid out.
The owner wants me to make the Deep Switch into a bright switch. He wanted two separate channels, and make them a High and Low input separately for different guitars. Will it be a big deal if the inputs are not parallel.? I guess what I am asking is, is it better to make the cat and plate variations switchable, than it is to just just have to change from one input jack to another.?
He also did not want to add any holes, pots or switches. I was just trying to give him two different/separate channels he could plug into on the bass channel that he never used anyway.
His amp still has the Normal channel also. I am sure I will have to make some changes for him, but I first wanted to make sure the amp will at least work the way I have it wired. Then I know I have a working amp I can do something with per my friends desires.
I really appreciate all the help and suggestions from everybody. I do not play guitar, so I Really Do Appreciate the input. Feel free to make any other suggestions you feel would help.
Thank You

If those two inputs were completely separate (like on a switch) you would hear almost zero difference between the 350pF/56K and the 250pF/33K. As it is, they still interact (with just 89K between the inputs) so the difference will be even less. No point whatsoever.

Both channels have hi/lo inputs stock, so IMO it's better leave the conventional setup to accomodate different guitars and make the tone shaping all switchable. If you replace both volume pots with the 1M switched types and put the bright switch cap there, that frees up both of the slide switches to do other things (switchable slope, switchable cathode bypass, etc.) If you take care to keep the channels in phase, you friend will also be able to bridge them and dial in a sound with the volume pots (technically it would be better to decouple the two channels power supplies to do this, but it does work without that complication). The extra triode gives you all sorts of creative options: you could make one channel stupidly high gain by cascading another triode, though you'll have significant work to clean up the lead dress if you go that route. Or you could do the "Dave Funk" mod and wire a cathode follower between V1a and V1b and put the tone recovery stage on V2.

Investigating your idea of using the Deep Switch as a cathode switcher, and using the free triode as a cat follower for the tone stack.......
I am a bit out of my league as a engineer. Is it just a matter of making that free triode into a cat follower.? Or is there any consideration to things like B+ levels.? Does the B+ voltage need to change at all for me to be able to implement the CF, or do I just hook it up and go.? That is to say, if the nominal B+ happens to be 208 volts at the V1-V2 plates....is that good enough for the CF, I just tie right into that.? Or do I have to make any changes in the B+ dropping resistor to get more or less voltage for the plate of the CF.? Does the CF run off whatever plate voltage is there for the existing preamp tubes.?
Thanks

[Firestorm]

I think you would want to have V1a direct coupled to V1b and put the tone recovery amp on the unused V2 triode. Silverface Fenders tended to run the preamps hotter than previous models, so it would probably be best to increase the dropping resistor feeding them (you could split the rail and preserve voltage for the Normal channel if you have room for another cap somewhere -- there is a fair amount of space inside a Bassman). The gating factor is the heater/cathode voltage the tube will tolerate. In most modern tubes, especially some of the ones with spiral heaters, this voltage is lower than in classic tubes. The workaround is to elevate the heaters enough to minimize this differential.

[C Moore]

I think you would want to have V1a direct coupled to V1b and put the tone recovery amp on the unused V2 triode. Silverface Fenders tended to run the preamps hotter than previous models, so it would probably be best to increase the dropping resistor feeding them (you could split the rail and preserve voltage for the Normal channel if you have room for another cap somewhere -- there is a fair amount of space inside a Bassman). The gating factor is the heater/cathode voltage the tube will tolerate. In most modern tubes, especially some of the ones with spiral heaters, this voltage is lower than in classic tubes. The workaround is to elevate the heaters enough to minimize this differential.

Been gone all day at a mini tone fest....
OK, I get most of this. I will start on it tonight and be back for help when I get stuck
Thank You

[selloutrr]

Just a thought to make this super easy... ask if he has an amp in mind that gives the tone he is after.. instead of trying to reinvent the wheel and hoping you get close enough to make him happy. Just clone that amps circuit as one of the channels. I have a friend who just like yours is an excersize in self control.. I ripped him a new asshole this morning. it needed to happen but it didnt feel half as good as i thought it would.

hang in there it's a shitty ride...

[C Moore]

Just a thought to make this super easy... ask if he has an amp in mind that gives the tone he is after.. instead of trying to reinvent the wheel and hoping you get close enough to make him happy. Just clone that amps circuit as one of the channels. I have a friend who just like yours is an excersize in self control.. I ripped him a new asshole this morning. it needed to happen but it didnt feel half as good as i thought it would.

hang in there it's a shitty ride...

Oh....that's funny. I needed a laugh.
I think I will be OK. I really think you guys have put me ion the right track. With the suggestions I got, I think I can make the bass channel into something usable that he will like.
My thought was to:
1. Increase plate load resistor.
2. As Firestorm mentioned......use the "deep" switch to make the cathode switchable between two values of resistor/cap.
3. Use the un-used triode for a cat follower for the tone stack. I can probably just use the same stack as the normal channel. I think that will be a big enough departure from the Bass Channel to make him pretty happy.
4. And the cat follower is probably where I am going to need some help when I get there. Not sure if it will just fall into place, or if I am going to need another drop resistor/filter cap set up. Guess I'll find out when I get there.
I am using the PS Filtering of the AB165, and that has an extra filter compared to AA864. Maybe that will handle the addition of the CF.?
Thanks

[C Moore]

I think you would want to have V1a direct coupled to V1b and put the tone recovery amp on the unused V2 triode. Silverface Fenders tended to run the preamps hotter than previous models, so it would probably be best to increase the dropping resistor feeding them (you could split the rail and preserve voltage for the Normal channel if you have room for another cap somewhere -- there is a fair amount of space inside a Bassman). The gating factor is the heater/cathode voltage the tube will tolerate. In most modern tubes, especially some of the ones with spiral heaters, this voltage is lower than in classic tubes. The workaround is to elevate the heaters enough to minimize this differential.

OK, so back to the CF idea.
After the guitar inputs to V1a, I run that straight into the grid of V1b.?
Then I run that into the CF.? And then I run the CF into the Fender tone stack.?
I must be missing a step somewhere. What component(s) should be used to couple V1b into the CF.?
Thank You