Reverb on 124

[gary sanders]

Where should it start and finish?

[dreric]

Bump

I recently posed the same question to normster via PM as I remember seeing some layouts showing his one tube verb in some amps. (may have been the blue monkey) haven't heard back yet.

I'd to the question with how does verb work in this circuit w/o the dumblator as an interface?

Eric

[talbany]

Here you go..

Tony

[gary sanders]

Cool.Thanks!

[glasman]

FWIW,

You can get a large improvement in reverb performance if you bypass the B+ feed to the reverb transformer (red wire) with a .1uf 600V to ground.

Gary

[Max]

Where should it start and finish?

Hi gary sanders,

AFAIK Alexander Dumble placed the reverb stages in his amps with an OD circuit like this:

pre-OD reverb:

Sometimes he placed the reverb stages (driver, return, mix) in front of the OD circuit. This approach is perhaps a bit similar to using a Fender with built in reverb (or a stand alone reverb in front of it) and get harmonics and sustain by power amp saturation. In this kind of setup and in the "OD mode" the reverb part of the sound won't be very prominent in the moment of the first attack of the note but will get the more prominent the more the note decays. This delivers some kind of ducking effect (to some extent). Some pre-classic second generation ODR amps I am familiar with have such a kind of "pre OD" reverb structure. AFAIR these ODR have a bit less OD gain than the usual second generation ODS amps as an example and you will perhaps need some time and experience to dial in the sounds you are happy with. But IMO a very interesting approach with special merits.

post-OD reverb:

Sometimes he placed the reverb stages (driver, return, mix) between the clean/OD stages and the PI (/driver) stage(s). This approach is a bit more similar to using an outboard stand alone effect in the loop. AFAIK Alexander used this kind of placement of the reverb stages in some of his later (classic, skyline) ODR amps. One example is the ODS 150W. I've attached a pdf file of this kind of "post OD" reverb structure (file source: Schematic Heaven).

All the original Dumble amps with an OD circuit and reverb (with the exception of some of the modded Fender amps) I am familiar with in person or from pictures or have heard of use a three tube reverb structure (driver tube, return tube, mix tube).

Cheers,

Max

[gary sanders]

Good info.I like the idea about the pre OD and the "delayed"reverb

[Max]

I like the idea about the pre OD and the "delayed"reverb

Hi gary sanders,

ODR #013 is an example for an ODR with such a kind of pre-OD reverb structure. Three of the six preamp tubes are the usual V1, V2 (OD) and PI tubes. The other three are the driver, return and mix tubes of the reverb circuit.

The 100W ODR amps I know of with the post-OD reverb structure have the same number of preamp tubes. The ODS 150W has two additional tubes, one for the tremolo and one to drive the power tubes after the PI stage = 8 preamp tubes.

Here you find a discussion about ODR #013 with the pre-OD reverb: https://tubeamparchive.com/viewtopic.php?t=407

Cheers,

Max

[Normster]

FWIW, I would NOT use the 124 layout that Tony posted. I was experimenting with tube rectified 6V6s at the time. The amp worked, but was not a great sounding amp. (Sold it to a friend that loves it but I never cared for the tone that much.) Also, adding to what Gary said, the reverb as it's shown in that layout is very weak and thin. I've since started using a completely seperate node for B+ to the reverb driver.

[talbany]

I never cared for the single tube 12ax reverb either...This is the best one I have used (tweaked version of Eric's 6Bm8)..For whatever this is worth!!...On the edge of surf..
Been discussed to death here..

Tony

[gary sanders]

Well thats a weird little tube.

Im limited on space for tubes so Ill have to see what I can do.May can add one more and do a Fender-ish circuit

[gary sanders]

I think I even have a 6bm8 from an old stereo.hmmmmmm

[BobW]

Gary you could also try a 6AN8. It's what Dynaco used as their preamp/drive tube.

[heisthl]

Well thats a weird little tube.

Im limited on space for tubes so Ill have to see what I can do.May can add one more and do a Fender-ish circuit

If you can do 2 tubes, this is my fav reverb circuit:

[mat]

Well thats a weird little tube.

Im limited on space for tubes so Ill have to see what I can do.May can add one more and do a Fender-ish circuit

If you can do 2 tubes, this is my fav reverb circuit:

heisthl, would You put this before or after active loop and what reverb pan would You suggest for the circuit ?

Thanks,