Two different preamps (one octal and one regular) in a Tweed Delux "clone"

Jerry garrcia

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Hi all. I would like to have the possibility to shift between two preamps in one combo speaker cabinet, Tweed Delux, 5E3. One octal preamp (1x6SL7, 2x6SJ7) and one 12AY7+ 5751 preamp. Then 2x6V6 power tubes and a Weber 12A125 or a Jensen P12R Speaker.
1) Is that possible?
2) will it fit in a Tweed delux cabinet? If not, what is the minimum required tweed cabinet size?
3) if so what is the best solution to shift between the preamps? A switch?
I don’t want any external preamps even if it easier or cheaper.

Does anybody have a nice schematics/layout for this construction from a previous build?
 

BluegrassDan

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Hmmm. Interested to see what folks suggest.

The two greatest issues will be real estate and the switching itself.

Part of the mystique of the Deluxe is the interaction between channels.
 

Bobbyoso

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Not a whole lot of spare real estate in a std 5e3 chassis for a second preamp, but people build 3-mast clipper ships inside small bottles, so it may be doable.
 

Jerry garrcia

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Probably cheaper/easier/better to build two separate amps.
I agree but not as fun and practical. To get the "umpf" and warm octal preamp sound (from example a Gibson GA 20-50) and to be able to shift between the two kinds would make this the perfect gigging amp for Jazz gigs since it is quite light and would be able (in theory) to produce all of the nice sounds needed without the need for a massive pedal board. A hand built octal guitar amp is >$2000 from a specialized company if buying a new one like the Tribute.

If it is impossible to make it as good (focusing on clean tones) with a combined amp, then the two amp build would be better. But if it is doable to get the two preamps in a nice looking combo tweed cab with a 12 inch speaker, I'm all in.
 

Jerry garrcia

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Or if size is the problem with the two preamp solution, can a 5E3 be built within a Tweed Pro 5E5 cabinet for extra space?
 

archetype

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Or if size is the problem with the two preamp solution, can a 5E3 be built within a Tweed Pro 5E5 cabinet for extra space?

Sure. With a custom cab, the builder should be able to cut the top to fit a 5E3 chassis into anything that's big enough.

You're still trying to stuff 10 pounds of 5E3 circuit into a 5 pound chassis, though. Consider using another standard tweed chassis and plugging unused holes.
 

Jerry garrcia

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Sure. With a custom cab, the builder should be able to cut the top to fit a 5E3 chassis into anything that's big enough.

You're still trying to stuff 10 pounds of 5E3 circuit into a 5 pound chassis, though. Consider using another standard tweed chassis and plugging unused holes.
tnx. Do you have any suggestion for standard tweed chassis in different sizes? been searchin the web instead of working but without success. The only one I could find that was larger than the 5E3 with just one speaker was the Tweed Pro 5E5 cabinet.
 

boredguy6060

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You can make the cabinet as big as you like, there’s no rule
that states that you have to use the standard size cab.
If you have the know how there’s no reason why you couldn’t use two pre amps either.
Actually I really like the idea, that would be a killer amp for sure.
If you decide to do it, I love to follow along.
 

Jerry garrcia

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You can make the cabinet as big as you like, there’s no rule
that states that you have to use the standard size cab.
If you have the know how there’s no reason why you couldn’t use two pre amps either.
Actually I really like the idea, that would be a killer amp for sure.
If you decide to do it, I love to follow along.
Glad to hear that you also like the idea and think it could be a killer amp.
Just got a tax return so I’m doing it! I just need to redirect some of the cash to the “have fun account” with limited transparency from
My better half. It will probably be a quite expensive project…
ga-20.gif

00B5863C-34BF-4283-A7A7-84041B8086AA.gif
 

NTC

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How about a 5F8 tweed twin chassis with a cab for only 1x 12 or 15? 5 octal, 3 9 pin sockets.
 

AlfaNovember

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Interesting idea.

Seems to me that you could do the preamp switching with a 6-pole, dual-throw rotary switch with break-before-make switching. It would have to be a good sized one: 5 cm diameter, ceramic base, sturdy contacts, etc. Like the old HAM radio guys used in boatanchor radios.

If it were switched between the PI and the power tubes, something like:

pole 1: B+
pole 2: signal pos
pole 3: signal neg
pole 4: Ground
pole 5: feedback connections
pole 6: (bonus) different cathode resistors for the power stage. That GA-20 looks like it has a fixed bias? you'd likely abandon that for self-bias with a cathode resistor.

You would need to take the B+ for the grid, PI and preamp stages from 'downstream' of the switch, and have dedicated decoupling capacitors for both sides. Caps are cheap, so building extra RC networks isn't horrible.

With a big rotary switch, it would probably thump when you switched between sections. Might need to work out a solution to that.

I'd build it as a standalone. The chassis will be bigger, and I wouldn't want to risk a full combo cabinet if the whole thing proved unworkable.
 

boredguy6060

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OP, you need to try and enlist the help of RobRob. He is a genius and projects like this are his specialty. He is very much in demand. He has written extensively. Google RobRob with the goal of getting to his website,webpage.
You can write to him thru this Forum and explain what you are trying to achieve, give him some time and you’ll get some priceless info.
You’ve gotten the best advise and direction I have to offer, good luck and I’ll have my eye out watching your progress.
 

Jesco

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I think I would leave the PI and driver as one tube type or the other and just switch the preamp .

This is exactly what I was thinking! If you leave the PI as is, the switching would be a piece of cake. And though I am no expert on tube distancing, I would reckon you could fit another socket in the preamp section, no problem (the 12ax7s in my ao-35 ghia clone are awfully tight). That way, you don’t need any kind of special chassis or cab.
 




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