Mosfet reverb recovery

[Bieworm]

Hi guys

I’ve been looking a lot at circuits with mosfets substituting triodes in tube amps. I always end up with circuits that have a mosfet cathode follower, but I would like to try an IRF840 in the recovery part of an AB763 reverb circuit. Has anyone got a schematic for such application?

Thanks

[tubenit]

I know an LND150 is used as a recovery in active FX loop designs.  See reply #33 in FX loops from the ARCHIVES:


tube effects loop on board (el34world.com)


I have not used one, but I'm thinking that perhaps it could be used as a reverb recovery?


Hopefully, someone more knowledgeable can offer a more educated answer.


With respect, Tubenit

[Bieworm]

Is it an idea to test this on an amp doing the following?

Pull the recovery tube, clip in an LND150 mosfet on both triodes with each a back to back 12V zener from cathode to grid? And leave all other connections as they are. Or are there other values that would definitely need to be changed?

[DummyLoad]

Hi guys

I’ve been looking a lot at circuits with mosfets substituting triodes in tube amps. I always end up with circuits that have a mosfet cathode follower, but I would like to try an IRF840 in the recovery part of an AB763 reverb circuit. Has anyone got a schematic for such application?

Thanks

Sub the ckt at the top of the page for a triode gain stage - For reverb tank recovery, you don't need ZD1 & ZD2. An IRF840 to do the job is overkill.

http://www.hawestv.com/amp_projects/amp_solid_tube/fetpreamp_200v1.htm

--Pete

[Bieworm]

Hi guys

I’ve been looking a lot at circuits with mosfets substituting triodes in tube amps. I always end up with circuits that have a mosfet cathode follower, but I would like to try an IRF840 in the recovery part of an AB763 reverb circuit. Has anyone got a schematic for such application?

Thanks

Sub the ckt at the top of the page for a triode gain stage - For reverb tank recovery, you don't need ZD1 & ZD2. An IRF840 to do the job is overkill.

http://www.hawestv.com/amp_projects/amp_solid_tube/fetpreamp_200v1.htm

--Pete

Thanks Pete! That is exactly what I was looking for👍👍👍

[Greenwichpaul]

This thread includes a LND150 recovery stage that has been used successfully, last post.


https://el34world.com/Forum/index.php?topic=27722.0

[kagliostro]

In my archive I've this



Franco

See attached pdf

[tubeswell]

The Surfy Bear stand alone reverb is mosfet driven IIRC (it’s like a 6G15, but with fets instead of tubes). That’ll have a recovery stage. Schematic is floating around somewhere. If someone else hasn’t linked to it by the end of the day, I’ll attach the schematic file when I get back to my desktop thingy later.

[tubeswell]

(Edit - attachment deleted - schematic already posted in reply #6)

[tubeswell]

And the Surfy Bear (JFET)

[mat janssen]

Hi I think there is a problem in the drawing of the phase inverter. The 1M resistor shoud be connected to pin 7 of the 12AX7 and the other point of the capacitor 10nF to ground?

[PRR]

Hi I think there is a problem in the drawing of the phase inverter.

In reply #7? 6 Yes, there is.

Reply #6 and #8 it seems.

Typo, thanks.

[tubeswell]

Hi I think there is a problem in the drawing of the phase inverter.

In reply #7? Yes, there is.

Reply #6 and #8 it seems.

[DummyLoad]

And the Surfy Bear (JFET)

Would be nice to know what type PNP Q1 is - Assuming BC556 or similar.

--Pete

[PRR]

And the Surfy Bear (JFET)

Would be nice to know what type PNP Q1 is - Assuming BC556 or similar.

"Silicon"?

It doesn't look fussy. >6V, >0.7mA, Vbe near 0.6V. You could probably put it in backward (E and C reversed) and it would play OK.