Pentode in V1 of 5E3

[Codymobley]

All,

I've gotten it into my mind that I want to build a GA-40/5E3 hybrid. I've searched through the backlog of posts here and elsewhere looking for discouragement, but the worst news I've found is that it will be a quiet amp. I'm hoping to end up around 5-10watts so that doesn't bother me too much.

My thought is to use the 5879 preamp section of the GA-40 and marry it to the 5E3 to have interactive volumes with the tied together channels on V1. I'm worried that since the 5879 only has a single plate the interactive channels may be moot since they will be drawing from the same plate at the same time. The values of the tone and volume pots, gridstoppers, bypass resistor, etc. have been changed from the 5e3 circuit to those of the GA-40.

The V2 would be a 12AX7 acting as a para phase inverter just as in the 5E3, the rest of the circuit is unchanged.

To y'all's experienced eyes is this something feasible? Or should ai add a second gain stage to drive the 5879? The transformers will be the standard 5e3 recommended trannies.

Thanks!

[ChopSauce]

Your idea is interesting but its implementation requires probably (much) more work than you seem to having thought.

Notably:

One pentode -> 4 inputs...

One 12AX7 <=> 2 triodes -> 2 x 2 inputs(1 Hi, 1 Lo) sounds pretty sensible but the above much less...
(not to mention the expected interaction)

Why not (2 inputs), otherwise...

A schematic might help having a more clear view.
(plus you should locate the master volume closer to its related portion of the circuit)

[Codymobley]

Sorry, I have attached the edited wiring diagram now to the original post.

[Codymobley]

I don't think it will work, but I'm hoping more experienced eyes will see something I don't.

[ChopSauce]

Yes, I saw the layout, but it is not the same thing.

I suggest you start from here

Modified Schematic.jpg

copying the input section of the pentode alone and then see how to mate it to

fender-tweed-deluxe_5e3_Schematic_Clean.gif

after one of the first (.1-400) coupling caps.

forgetting all about the holes for the jacks and the pots in a first approach (then you may want to put the master volume where the tone is located, and so on).

[Codymobley]

Thank you for looking it over and your advice.

[pdf64]

The master volume you’ve got shown in post #1 doesn’t work very well. It’s main advantage is that it kinda works, and doesn’t require any additional circuit nodes (eyelet / turret).
With an added cap and the master volume control wired in a more conventional manner, it can work a lot better, see https://www.thegearpage.net/board/index ... t-33797990

[Codymobley]

Thank you, I'll keep this in mind for future use.

[ChopSauce]

The master volume you’ve got shown in post #1 doesn’t work very well. It’s main advantage is that it kinda works, and doesn’t require any additional circuit nodes (eyelet / turret).
With an added cap and the master volume control wired in a more conventional manner, it can work a lot better, see https://www.thegearpage.net/board/index ... t-33797990

Here it is:

image_25105.jpeg

Seems worth a try...

[jabguit]

The V2 would be a 12AX7 acting as a para phase inverter just as in the 5E3, the rest of the circuit is unchanged.


Thanks!

5E3 has a cathodyne PI. A 5C3 has a paraphase PI.


cheers,

[10thTx]

For consideration . I have NOT built this. IF the tone stack did not work as well as one liked, you could easily add a mosfet cathode follower to help implement the tone stack. I have found the mosfet in the cathode follower position to have NO negative impact on tone. https://el34world.com/Forum/index.php?topic=21873.0

There is a SCH editable schematic attached also.

With respect, 10thtx

[Codymobley]

Thank you for clarifying that. I'll look at the 5C3 a little closer.

The V2 would be a 12AX7 acting as a para phase inverter just as in the 5E3, the rest of the circuit is unchanged.


Thanks!

5E3 has a cathodyne PI. A 5C3 has a paraphase PI.


cheers,

[Jerry garrcia]

So fun that someone also wanted this combo. My goal with the design of the amp was to have the best of both worlds. The pentode is grid leak biased to give it that sweet octal sound. Then I use a 12ay7 as a triode due to the aim of the amp is mainly jazz through an archtop. Wanted the triode possibility to have the deluxe sound and to be able to use it with pedals. The grid leak biased pentode doesn’t like a boost pedal

I built this a couple of months ago. It’s a beauty and the 6sj7 really sings!
You have the possibility to run it with the triode or pentode. Started up with a switch to shift between the preamps but couldn’t get it to work. The whole switch circuit became a radio receiver. Tried with several different shielded cables but without success. In this schematic you can switch between the preamps with a A/B switch pedal if you need to switch while playing.
Used a 6SC7 as a PI and a solid state rectifier to free up a tube socket since it was designed to be built in a 5E3 chassis. A sag resistor to compensate for the lack of a 5y3 rectifier. Used a standard Hammond PT for a 5E3 circuit with 330 VAC. First filter cap a 500v.
A p12n speaker that handles the bit darker sound of the 6sj7 really well.

AFDE89A1-9CA9-4DA1-9912-5D1C953F4C35.jpeg

[jabguit]

AFDE89A1-9CA9-4DA1-9912-5D1C953F4C35.jpeg

Where does the "D" B+ node come off of?

[Jerry garrcia]

7396070F-1D8F-4A7B-ACF8-E2DE63CC48A1.jpeg

FE07091A-6C2A-4071-8A15-10DDB0BEF2A9.jpeg

DA284038-EFCF-4AEA-BC47-90580DD08584.jpeg

Sorry. “D” and “C” are the same. Both preamp tubes get the same voltages.
B+1/2/3 without tubes. 478/477/468 VDC.
B+1/2/3 with tubes 378/322/229 VDC