Pentode in V1 of 5E3

[Jerry garrcia]

Doing a lower wattage version as of now. With a spring reverb. Modded a F2a chassis. Used a LNDVerb for the reverb driver

432CEDA3-4ED3-4A60-9FC4-2FAC4317B185.jpeg

[Phil_S]

In 2009, I built something similar. I thought Jimi reincarnated was inside the amp. I liked it, but it wasn't clean. I don't think I've fired it up in quite a few years. Life gets in the way.

[Jerry garrcia]

@Phil_s Nice one. What did you use for v1? Another 6sj7?
Want to build a GA-20/30 with two preamp tubes, one cathode biased and one grid leak biased. Then 6SC7 PI and speakers like the GA-25/30/50, one 8” and one 12”.
Bad on producing layouts. Not interested in point to point build but turret based.

[jabguit]

7396070F-1D8F-4A7B-ACF8-E2DE63CC48A1.jpegFE07091A-6C2A-4071-8A15-10DDB0BEF2A9.jpegDA284038-EFCF-4AEA-BC47-90580DD08584.jpegSorry. “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

That's a nice looking amp!

cheers,

[Phil_S]

@Phil_s Nice one. What did you use for v1? Another 6sj7?
Want to build a GA-20/30 with two preamp tubes, one cathode biased and one grid leak biased. Then 6SC7 PI and speakers like the GA-25/30/50, one 8” and one 12”.
Bad on producing layouts. Not interested in point to point build but turret based.

V# labels are sloppy. V2 is really V1, etc. That schematic is the whole amp. As I recall, I started in one place and ended in another. I didn't change the labels. I worked on the dropping resistors for the 6SJ7 plate supply to raise it up as much as I could. The original lower voltage was fizzy as I recall.

I chose the 6SL7 over the 6SC7 because I didn't care for the shared cathode of the 6SC7, and tube characteristics are about the same. Also, I already had a 6SL7.

[Tobyk]

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!

I’ve tried this, or very similar.
I made a Gibson GA19 clone, which has a cathodyne PI.
Channel two was taken from GA20T tremolo channel (whithout the tremolo!), which is 5879, into the same PI.
The result was underwhelming in terms of differences. Even though the 5879 had a 510K (!) plate resistor, the gain was lower than the GA19 channel (which uses a 12ax7 in v1, with a 470K plate resistor).
Tonewise I can’t hear any difference between the two tubes. But yes, a gainy amp for sure, like a hotrodded 5E3!

[Tobyk]

@Phil_s Nice one. What did you use for v1? Another 6sj7?
Want to build a GA-20/30 with two preamp tubes, one cathode biased and one grid leak biased. Then 6SC7 PI and speakers like the GA-25/30/50, one 8” and one 12”.
Bad on producing layouts. Not interested in point to point build but turret based.

You could put that grid leak bias on a switch instead, will save you half a tube (or a whole tube, depending on what you use)! I did that in a build recently.

[Tobyk]

In 2009, I built something similar. I thought Jimi reincarnated was inside the amp. I liked it, but it wasn't clean. I don't think I've fired it up in quite a few years. Life gets in the way.

Been wanting to do exactly like your schematic!
But wondering if it’s worth it – will it sound just like yet another 5E3 or will the grid leak bias/paraphase combo add something special?

[Jerry garrcia]

@Phil_s Nice one. What did you use for v1? Another 6sj7?
Want to build a GA-20/30 with two preamp tubes, one cathode biased and one grid leak biased. Then 6SC7 PI and speakers like the GA-25/30/50, one 8” and one 12”.
Bad on producing layouts. Not interested in point to point build but turret based.

You could put that grid leak bias on a switch instead, will save you half a tube (or a whole tube, depending on what you use)! I did that in a build recently.

So funny. I built an amp a couple of month ago with a bias switch for a 6SJ7 to be able to switch between grid leak and cathode bias. Works actually well. And the other channel was a cathode biased 6SC7. Will try to find the schematic.

88367B29-FD99-48DB-A5CC-0A49783AA66D.jpeg

Now on the final stretch on powering up a modded EH-185 circuit with a 6SC7 as the second gain stage of the mic channel and the first and only for the instrument channel just to save a tube due to lack of space in the chassis. A 6SN7 PI instead of the 6N7. Added a mosfet reverb driver, for a reverb tank before the PI.
Struggling with the voltages that are a bit high since I’m aiming for 288V at the plates for the 6L6’s, 185V for PI and 135V for the preamps. Will get there but work and family life is in the way
PT 300-0-300VAC AND Voltage drop resistors 10K, choke and 100K.

061D92F0-A49E-4946-B8D9-417712D1E69E.jpeg

[rooster]

Here's maybe some odd input. A long, long time ago I ran into (and purchased) an original Fender 'Woody' amp, circa 1948 (I was told). It had the etched K & F Thunderbolt logo on the black metal chassis control panel. It had a silver 10" Jensen alnico speaker with the output transformer attached to the speaker frame. The chassis sat on the bottom of the case. It had two volume knobs and one tone knob.

OK, I eventually sold the amp, and, since I've never met anyone else who owned one, I was never able to document if the behavior this amp had was typical. It had an Instrument channel and a Mic channel. Anyway, as I recall, it was the instrument channel that I plugged into - and - if I turned the Mic channel up (simultaneously) the preamp gain would virtually double. Somehow one channel was cascading into the other channel. This interaction created a super cool sustaining overdriven guitar sound with a HB pickup. It easily created controllable feedback, too. I also remember that I had to buy glass encased preamp tubes (it came with metal cased versions) because when I used it in this high gain mode, the metal cases would just ring.

Is this the amp circuit the OP is trying to replicate? Was this gain that occurred just the behavior/nature of the 6SC7 tube and the circuit?

[jabguit]

7396070F-1D8F-4A7B-ACF8-E2DE63CC48A1.jpegFE07091A-6C2A-4071-8A15-10DDB0BEF2A9.jpegDA284038-EFCF-4AEA-BC47-90580DD08584.jpegSorry. “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

Nice! I like it!
Reminds me of my "Little Giant Killer" (5E3 with 5E5 iron; 6L6/5881 capability/ 10" Ragin' Cajun):

LGK_02.jpg

[martin manning]

There's this, which morphs an EF86 between triode and pentode operation: http://www.valvewizard.co.uk/ef86pcb.html

[Phil_S]

In 2009, I built something similar. I thought Jimi reincarnated was inside the amp. I liked it, but it wasn't clean. I don't think I've fired it up in quite a few years. Life gets in the way.

Been wanting to do exactly like your schematic!
But wondering if it’s worth it – will it sound just like yet another 5E3 or will the grid leak bias/paraphase combo add something special?

It makes me sound like Jimi Hendrix, however, I don't have Jimi's chops, so I'm not suggesting plugging into this amp makes me a guitar god. I'm talking about tone. No, it is not at all like a 5E3.

[Tobyk]

7396070F-1D8F-4A7B-ACF8-E2DE63CC48A1.jpegFE07091A-6C2A-4071-8A15-10DDB0BEF2A9.jpegDA284038-EFCF-4AEA-BC47-90580DD08584.jpegSorry. “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

Nice! I like it!
Reminds me of my "Little Giant Killer" (5E3 with 5E5 iron; 6L6/5881 capability/ 10" Ragin' Cajun):

LGK_02.jpg

Nice looking amp. Looks like you decided not to use cleves for the upper back panel and have the chassis meet the cab sides for minimal width. Any special reason for this?

[jabguit]

for minimal width.

Right there...