12AT7 driven outboard reverb unit?

[Dingleberry]

Hi.

I have fender reverb transformer and matching tank lying around and I was wondering has anyone of you made an outboard reverb unit alá 6G15 but instead of 6K6 or 6V6 using 12AT7 as driver alá Fender amps?

I'll have few power transformers from old tube radios and some of them would probably suit well for that project too so it's halfway there already;)

Do you have any suggestions or "ready" schematics or should I just combine Fender amp reverb and 6G15 circuit and tweak it to taste?

-T

[Alexo]

I've done it, not too much else to it. I think the AT7 will reach full power and overdrive a lot sooner than a 6K6, so you either have to modify the dwell control with series resistor, or drop some gain somewhere along the line. Worked out pretty darn well too, have fun!

[Dingleberry]

Thanks for reply Alexo.
Lotsa new questioins;)
Did you have one or two gain stages before AT7?
It probably will be able to drive the AT7 with one gain stage also.
Do you have a schem drawn?
Did you follow the 6G15 schematic and just mixed it with fender amp reverb driver part?

-T

[10thTx]

Don't know if you saw this post ?:

https://tubeamparchive.com/viewtopic.php?t=13194

You could build this and leave off the FX loop if you wanted. It goes into a passive effects loop prior to the phase invertor.

With respect, 10thtx

[Dingleberry]

Hi 10thtx.
I actually saw that post when I was using the searc function of this forum.
That will probably be one good driver stage option.
Just have to convert it to stand alone unit use (before amp input) which won't be a problem using 6G15 topology as a rough guide. Just have to be aware not overdrive the 12AT7 into serious distortion as Alexo pointed out. Gotta fiddle with gains in the preamp. I was also thinking to make it switchable between two tanks with different decay times (medium and long) to get the most versatility out of it.
I have a chassis and a head cab which could just fit those two tanks.
Any opinions about that one?

-T

[10thTx]

I don't know about the outboard 6G15 unit, so I don't know how to advise you about your idea?

I didn't notice you mentioning what kind of amp/s you'd use this with? IF you're using a reasonably clean (not overdriven amp) then placing reverb at the input may get you exactly the tone you want.

Having said that ..............
I personally don't want reverb being overdriven and prefer an overdriven tone being reverbed later in the signal chain. That's why I like the insertion point of using a passive effects loop just prior to the LTPI. And while I like surf music, I don't play it and don't have need for very intense reverb.

Just a thought. With respect, 10thtx

[Alexo]

Thanks for reply Alexo.
Lotsa new questioins;)
Did you have one or two gain stages before AT7?
It probably will be able to drive the AT7 with one gain stage also.
Do you have a schem drawn?
Did you follow the 6G15 schematic and just mixed it with fender amp reverb driver part?

-T

I had two gain stages, but I used a 12DW7, so one of them was a pretty low gain stage. I am still easily able to overdrive the AT7 by turning up the dwell control, which is a surprisingly cool sound... but you might be able to get away with a single pentode gain stage or maybe a cascode, I think just a single AX7 stage in front of the AT7 may not give you quite enough oomph for all situations, but two is probably too many.

The schematic's in my head but yeah, it's basically a 6G15, but the 6K6 is subbed by the reverb driver you'd find in just about any old Fender amp.. except I like to bias them a little warmer.

[Dingleberry]

I'm gonna use it with amps set clean. It'll always be last in my siganl chain before amp input.
I've got few different tube amps without reverb mostly small (5-20W) combos. I don't play surf either but sometimes I need grand canyon reverb just to use as an effect mostly in studio sessions. On the other hand for live use I usually need just little subtle hint of verb. That's why I was thinking to make it with two different tanks so I could make it as versatile as possible.

-T

[Alexo]

I'm gonna use it with amps set clean. It'll always be last in my siganl chain before amp input.
I've got few different tube amps without reverb mostly small (5-20W) combos. I don't play surf either but sometimes I need grand canyon reverb just to use as an effect mostly in studio sessions. On the other hand for live use I usually need just little subtle hint of verb. That's why I was thinking to make it with two different tanks so I could make it as versatile as possible.

-T

Haha I built an amp a while back with 2 different tanks and a blend pot to go between them. Interesting experiment, but the differences turned out to be so subtle that I basically canned the project once I had it up and running - takes a lot and gives you a little.

Not that the 2 tanks did not sound different, but upon mixing them, one very quickly dominates the sound, and you really wouldn't notice if the other was just disconnected. So it just becomes a choice of a long delay or short delay tank, and imo, the long delay tank gets a little too cloudy and discordant for most guitar-oriented applications.

By adjusting the dwell, mix and tone controls on a 6G15-ish circuit, you can go from grand canyon to subtle ambience pretty easily, imo. Not that there isn't room for improvement in the 6G15. But don't let me stop you!

[10thTx]

Here is a DRAFT idea that I have not built. It draws heavily from Heisthl's FX & Reverb idea.

I tend to like more mids reverbed since I use subtle amounts of reverb. So if you tried this, you might want a 500-680p going into the 12AT7. And you might want to try lower value coupling caps for the 12AX7.

With respect, 10thtx

[Alexo]

That is a massive amount of reverb recovery gain! Personally, I would use the extra gain stage in front of the AT7 (maybe - depends on what is actually in the hidden "preamp" section.

More gain in front of the tank vs. after it gives you a better signal to noise ratio, and a surfier sound. Less signal into the tank = more ambience.

[Dingleberry]

That is a massive amount of reverb recovery gain!

That's what I was thinking too.
I think that I'm gonna follow the 6G15 topology using two gain stages before driver and adjust the preamp stage gains that I don't overdrive the 12AT7 into distortion.

-T