Single tube reverb in a Marshall

[eddie25]

I saw the plans for the single tube reverb on the Hoffman forum (http://www.el34world.com/Forum/index.php?topic=7957.0) and I'm very interested in trying this out in a 100w Marshall 1959 build at the request of a friend.

Anyone ever tried this?

I've come up with a board layout that I think would work, but I'm considering options for the 'send' triode plate voltage, (also known as the red wire from the reverb transformer). Most of the examples connect it right after the choke, at the screens cap, but they are also generally lower voltage amps. So should I just move further down the line and connect to the PI cap to get a lower voltage? Should I add a node to the B+ dropping string? Or, should I maybe branch off the B+ string, like a separate 20K resistor and a 22uf cap splitting off after the choke, but keep everything else the same?

For the return triode plate I think I would stick with using the last node on the B+ rail.

I've noticed that many amps have their reverb tubes at way over max plate voltage, but I'm feeling like I'd rather keep it lower for reliability, or is there reason NOT to worry about it in this case? Hopefully I can learn something here.

Thanks

[Alexo]

Or, should I maybe branch off the B+ string, like a separate 20K resistor and a 22uf cap splitting off after the choke, but keep everything else the same?

This is what I would do. Doesn't interfere with the rest of the power supply string by pulling extra current through it, gets the right plate voltage, and its own cap ensures it won't interfere with other stages via motorboating or whatever.

However, if you're building from scratch, I might just redesign everything so that it's more integrated and doesn't feel as much like a band aid.

[Structo]

Yes having it's own power node would seem the best, that way it is decoupled from the rest of the power supply.

[eddie25]

Well, I'll try that first and see how it goes.

It is gonna be a scratch build, so if you know of any other one tube reverb circuits, I'm all ears. The layout I am currently working on seems fairly neat, I'm ditching the dwell pot for fixed values. Hopefully the verb sounds good and doesn't mess with the tone. Thanks fellas.

[topbrent]

I would take a good look at the Rocket W/Reverb amps for your build ideas.

Study the layouts and schematics in this thread and you will be well on your way:
https://tubeamparchive.com/viewtopic.ph ... c&start=30

Look close and you will see where to sub the marshall pre/PI values, ...fixed bias, ect... tweak to your "marshall" taste.

The Rocket W/Reverb will provides the architecture and framing, go ahead and hang the Marshall drywall and wallpaper and you should be fine.

[Normster]

The 1-tube reverb is also used in several Mesa amps if you need examples. The best example I know of for a Marshall implementation is the Pignose 60VR. It's a simple take on a 2204 MV and sounds VERY good.

[Normster]

The problem with implementing the Rocket Reverb circuit is the NFB on the PI. On non-NFB PIs, it's easy to return the reverb to the bottom of the PI, but NFB will play havoc with that circuit. Andy Fuchs advised me once that it CAN be done, but I'd probaly need an engineering degree to follow the steps he outlined.

[eddie25]

Yeah, I thought about that with the 'rocket reverb' circuit, which is why I've been set on the 'hoffman forum' single tube reverb, with one knob. Wish I could post my layout, but it's full size hand drawn on grid paper right now. A little nervous how it will sound, but I guess you gotta give it a go and see. I'm just about finished planning and was gonna start drilling the board in a few days, but I'm all ears for suggestions. I couldn't find a schem for that pignose amp unfortunately. (EDIT: HA, I wasn't signed in when I first read your post, thanks for the schem!)

[eddie25]

Well, now you've thrown me for a loop. The reverb in the pignose looks pretty clever as well. I wonder if that is with a standard AB tank and Fender style transformer?

I noticed they take the power from the screens tap as well, but it's 357V I think (why is that the only voltage reading on the schem?). I'm expecting more like 450V on the screens of a Marshall. So far, in my layout I've set up a branch from the screens like I mentioned before.