Transformerless Reverb

[drewspriggs]

Howdy,

Looking at options for transformerless reverbs, and want to stick with tube driven (1 if possible). There seems to be two approaches I've seen from the searching I've done:

Swart/Ampeg - Swart use a 12DW7, with second triode for drive and first for recovery, whereas Ampeg use a 6SN7.
Channel Road Amps/Valve Heaven - pentode to drive the tank, triode for recovery. VH use separate tubes for each, where Channel Road suggest using something like an ECL82.

Aside from tube cost/availability, and assuming I can buy whatever pan I need, are there any inherent advantages/disadvantages to either approach? The plan was to put it onto a modular board similar to the Valve Wizard ones, with the input of the board handled by a MOSFET buffer/splitter and a mix control to combine the dry/wet at the end.

[mountainhick]

I've done 12DW7, works great for my needs.

I have not used a mosfet to integrate, just standard insertion into a signal path with mix resistor and cap.

Do you have a schematic of the amp you want to build or mod with reverb?

[sluckey]

Here's another reverb circuit that you don't see often. Works great and sounds good. Not as splashy as the typical Fender AB763 circuit.

[Yerffej]

Traynor YRM-1 uses an el84 coupled through a 10uf cap and sounds great. Aside from that and the slightly unique power supply, it's a great blackface clone.

https://schematicheaven.net/bargainbin/ ... r_yrm1.pdf

[nuke]

The reverb pan is going to be the tricky part. You need one with a drive coil of a suitable impedance value to match up well with the load impedance the drive tube wants to see as a load.

The datasheet for the 6BQ5 shows triode connected, it wants to see a 3500 ohm impedance, with a plate supply of 250 volts. Traynor is running that 6BQ5 at a lower plate supply and I can't really make out what it says the pan's coil DCR is, but maybe it says 180-ohms. So probably at 1khz, maybe 2500-3000 ohms. They put a relatively big DC blocking capacitor on it and a plate load resistor of 15k/10watts. Everything else looks about right to match up with the data sheet.

But you'd need to find the right pan. The return side, not that critical, just setup the recovery amplifier to mate with it.

[drewspriggs]

The reverb pan is going to be the tricky part. You need one with a drive coil of a suitable impedance value to match up well with the load impedance the drive tube wants to see as a load.

The datasheet for the 6BQ5 shows triode connected, it wants to see a 3500 ohm impedance, with a plate supply of 250 volts. Traynor is running that 6BQ5 at a lower plate supply and I can't really make out what it says the pan's coil DCR is, but maybe it says 180-ohms. So probably at 1khz, maybe 2500-3000 ohms. They put a relatively big DC blocking capacitor on it and a plate load resistor of 15k/10watts. Everything else looks about right to match up with the data sheet.

But you'd need to find the right pan. The return side, not that critical, just setup the recovery amplifier to mate with it.

That's the easiest part tbh - Accutronics has plenty of tanks available

[nuke]

That's the easiest part tbh - Accutronics has plenty of tanks available

They have lots of part numbers, but putting hands upon the needed configuration can be a much more difficult, especially if it is an odd ball configuration.

[TUBEDUDE]

I've become fond of the constant current pentode fed into an FB tank.

Screenshot_20260423_135315_Gallery.jpg

[didit]

Hello --

These all are at least adequate options.

I have gone on down the Channel Road. Single 9 pin, both driver and recovery, fits well. The solid circuit engineering helps both understanding and confidence. That constant-current driver mates with tanks ranging easily from 300-2000 ohm impedance. Recovery triode has good gain to match mixing with the "dry" signal. A 6GH8A is a fine choice, but there are several similar that'd work fine. Clean NOS can be had for about $10 each or less. Mod sells a good set of new tanks with 800 ohm input to fit most applications. Personally recycled older tanks harvested from organ and a Peavey amp.

FWIW.

Best ..

[TUBEDUDE]

Hello --

These all are at least adequate options.

I have gone on down the Channel Road. Single 9 pin, both driver and recovery, fits well. The solid circuit engineering helps both understanding and confidence. That constant-current driver mates with tanks ranging easily from 300-2000 ohm impedance. Recovery triode has good gain to match mixing with the "dry" signal. A 6GH8A is a fine choice, but there are several similar that'd work fine. Clean NOS can be had for about $10 each or less. Mod sells a good set of new tanks with 800 ohm input to fit most applications. Personally recycled older tanks harvested from organ and a Peavey amp.

FWIW.

Best ..

I initially tried the 6AW8, but had issues with it. The 6U8 worked well as did the 7199, but they are rather spendy now. The 9FB long tanks sounded the best.

[drewspriggs]

This is the general gist I had - was originally looking at the 6GH8A ala Channel Road, but realised the triode needs a stack of current for reasonable gain so I reckon it's off the table. ECL82 would be an easy choice and threw some values in for the recovery stage based on what I've seen, but 300v might be a pinch high.

The 12DW7 is still an option, but I can get any of the tri/pent tubes for about 1/2 the price from way more sources, so probably want to stick with that for now.

[jbrrrrr]

There's quite a few projects around here and EL34world that utilize 6BM8 single-tube no-transformer reverb circuits if you do a search for that as well as ECL82 - you can find some starting points that might be a decent place to start tinkering from.

[didit]

I initially tried the 6AW8, but had issues with it. The 6U8 worked well as did the 7199, but they are rather spendy now. The 9FB long tanks sounded the best.

NOS 7199 and 6u8 drained off by audiophiles with Dynaco and Dynaco derivative kit. The 6GH8 is a favoured near equivalent. The honest ears on various boards report little to no difference in performance. At this price what’s in the way?

https://www.surplussales.com/items/1500 ... cuum-tube/

Curious to know more about issues encountered with 6AW8 as on “paper” there’s everything to recommend it.

6BM8 based designs would be cool. Possibly overkill but that’s manageable. The reverb design I initially followed into this constant-current rabbit hole was built around one.

..

[TUBEDUDE]

I initially tried the 6AW8, but had issues with it. The 6U8 worked well as did the 7199, but they are rather spendy now. The 9FB long tanks sounded the best.

NOS 7199 and 6u8 drained off by audiophiles with Dynaco and Dynaco derivative kit. The 6GH8 is a favoured near equivalent. The honest ears on various boards report little to no difference in performance. At this price what’s in the way?

https://www.surplussales.com/items/1500 ... cuum-tube/

Curious to know more about issues encountered with 6AW8 as on “paper” there’s everything to recommend it.

6BM8 based designs would be cool. Possibly overkill but that’s manageable. The reverb design I initially followed into this constant-current rabbit hole was built around one.

..

Yes, many cheap pentode/triode tubes out there. Just find one with triode gain 70 or greater. Many have low gain.
The 6AW8's i tried each had hum issues. Tried everything but D.C. heaters. That might do it but i'm not willing to go that far unless it's already needed in a high gain build.

[didit]

Hmm --

Yes, many cheap pentode/triode tubes out there. Just find one with triode gain 70 or greater. Many have low gain.
The 6AW8's i tried each had hum issues. Tried everything but D.C. heaters. That might do it but i'm not willing to go that far unless it's already needed in a high gain build.

Depressing but unsurprising within a "developed for television" category of tubes. Triode gain of ~40 seemed adequate fir full recovery in my prototype of the Channel Road design, but any types with much lower specs one should be skeptical of.

..