Questions about one-tube reverb circuit

[Diverted]

Hi all,

This is the preamp/tone/reverb circuit in a Benson Monarch Reverb. One-tube reverb, no reverb transformer, just a tank and 7247 tube. The input comes from preamp plate 1, and the output goes into preamp grid 2 just before the paraphrase phase inverter, and on into 2x6V6.

I've heard this reverb and tone circuit and like it. Just wondering if incorporating it into a single-ended amp will be OK. I'm not sure if the reverb circuit sucks gain as the Fender reverb does, or if there are other things I probably should be thinking about but am not (probably!). Thanks.

[shooter]

https://el34world.com/Forum/index.php?topic=7957.0

[roarshock]

The thread that shooter posted is a treasure trove. To answer your question directly, yes that circuit will work, but you'll need a recovery stage (like the other triode of V1) before sending it to your power tube of choice. As far as gain suck goes, you'll have to be the judge.

[Diverted]

Thanks, my plan was to build the circuit just as shown in the schematic. Only difference would be that instead of going to the phase inverter following preamp second stage, it would go to the output tubes directly.

I have been reading through that thread and it looks very informative! I just have not found info yet on this circuit. The ones I've seen in the thread either involve the use of a reverb transformer, or incorporate a 6BM8 pentode/triode. The schematic I'm using calls for a dual triode 7247. I will do some more reading!

[Latole]

Thanks, my plan was to build the circuit just as shown in the schematic. Only difference would be that instead of going to the phase inverter following preamp second stage, it would go to the output tubes directly.

IMO like that , this reverb circuit will not have enough gain.
Less gain than if you go to the PI.

[pullshocks]

I've heard this reverb and tone circuit and like it. Just wondering if incorporating it into a single-ended amp will be OK. I'm not sure if the reverb circuit sucks gain as the Fender reverb does, or if there are other things I probably should be thinking about but am not (probably!). Thanks.

Well, Benson does exactly that with the Nathan Junior--1 6v6, 1 12ax7, 1 12dw7. Nathan Junior Reverb Combo — BENSON AMPS


The

[Latole]

I've heard this reverb and tone circuit and like it. Just wondering if incorporating it into a single-ended amp will be OK. I'm not sure if the reverb circuit sucks gain as the Fender reverb does, or if there are other things I probably should be thinking about but am not (probably!). Thanks.

Well, Benson does exactly that with the Nathan Junior--1 6v6, 1 12ax7, 1 12dw7. Nathan Junior Reverb Combo — BENSON AMPS


The

No solid state preamp ?

[pullshocks]

Edited 4/3/25:


The way Benson taps the reverb after v1A v2A  and mixes it back into V1B V2B (the second triode of the 12AX7, not shown in the schematic in post ##1), V1B V2B does double duty as the recovery stage and second gain stage.

[pullshocks]

OP--have you played through a Benson Monarch, or just heard internet demos?

[Latole]

The way Benson taps the reverb after v1A and mixes it back into V1B, V1B does double duty as the recovery stage and second gain stage.

Where do you read that ? Or you have the schematic ?

[pullshocks]

I bread boarded the monarch schematic from Amp Garage. 

I thought the clean and overdrive amp sounds were great.  The reverb was just ok.

Here are some comments I made in another Monarch-related thread about the experience with that schematic.  I considered trying a low watt version, but did not.  After listening to demos of the Monarch and the Nathan Junior, I decided not to pursue a low watt version.

Some issues, like the voice switch were wrong in the originally postesd schematic but got worked out (I'm not the one who solved the problem).   I got a version of the circuit working on my breadboard back in 2021.  Great sounds, but afflicted with the dreaded “bleed through” weirdness.  As stated above, the 5 node power suppy seems to largely solve the bleed through issue and AFAIK Benson now uses a 5 node power supply.  I wonder what the early  real Benson Monarchs with the 3 and 4 node power supplies were like.Some people reported loving their builds from the available schematic, and did not mention the bleed through and hum issues that afflicted others of us.  Maybe they didn't have the problems, or corrected them and did not report how they did so.  Or they felt the good qualities of the amp outweighed the issues, and they just decided to live with it“Hoodnight” tried to pull the available info into a schematic and layout he posted here:  Benson Monarch Reverb - The Amp Garage .  It includes a 5 node supply, and from my experience it may well turn out to be a “definitive” schematic.  But I haven't built it and I don't know for sure.  There have not been any updates or build reports on that thread since he posted it over a year ago.In my breadboard build, I love the full, rich tone at low volumes.  The overdrive sounds are great too, but I just play at home and the sound pressure levels are too high for my use, at least not without an attenuator.   I think the American/British switch works well, and gives 2 good sounding voices.  Last time I looked at the Benson web site, they had updated the Monarch with a bass control instead of the switchSo the 6V6 push/pull Monarch is overkill for my needs, and I will not be doing a permanent build.  After listening to demos of the Monarch and the Nathan Junior, I decided not to pursue a low watt version.  After all that work, I hate to walk away from it, but I need to try something else on the breadboard.  So I'm about to say goodbye to the Monarch.


Want to add preamp out to Monarch circuit

[SEL49]

The way Benson taps the reverb after v1A and mixes it back into V1B, V1B does double duty as the recovery stage and second gain stage.

That doesn't happen. No magical mixing going on. V1A is a cathode follower used to drive the tank and V1B is used as a recovery amp. V1B is NOT a second gain stage.

[pullshocks]

The way Benson taps the reverb after v1A and mixes it back into V1B, V1B does double duty as the recovery stage and second gain stage.

That doesn't happen. No magical mixing going on. V1A is a cathode follower used to drive the tank and V1B is used as a recovery amp. V1B is NOT a second gain stage.

Oops the image in post 1 does not show v1B. I’ll post  the complete schematic showing how the dry and wet signal paths meet at v1B

[SEL49]

Oops the image in post 1 does not show v1B. I’ll post  the complete schematic showing how the dry and wet signal paths meet at v1B

Sure it does. Your schematic does not label the tubes.

[Diverted]

OP--have you played through a Benson Monarch, or just heard internet demos?

I've played through one ... a friend owns one and left it with me for a few weeks. It's a great sounding amp ... I love the tone control pot/switch, super versatile.

[Diverted]

Pullshocks, I read that thread. I have a more recent version, with five filtering nodes.
One thing I noticed on previous schematics, and in your reply just now about reverb just being OK.
All schematics I saw show a 500K reverb pot. I reverse engineered the amp and traced out every component. The one I had, and the one I just built, has a 1M reverb pot and it can get very reverby!

[pullshocks]

Pullshocks, I read that thread. I have a more recent version, with five filtering nodes.
One thing I noticed on previous schematics, and in your reply just now about reverb just being OK.
All schematics I saw show a 500K reverb pot. I reverse engineered the amp and traced out every component. The one I had, and the one I just built, has a 1M reverb pot and it can get very reverby!

Cool. Did you check the setting on the paraphrase phase inverter pot?
What are your plans for a low watt version?

[pullshocks]

Oops the image in post 1 does not show v1B. I’ll post  the complete schematic showing how the dry and wet signal paths meet at v1B

Sure it does. Your schematic does not label the tubes.

SEL49–You are right. I failed to notice that the partial schematic in the first post labels the 12dw7 as  V1. Since the input goes to the 12ax7, I always referred to the 12ax7 as v1. But you are also right that the schematic I posted did not designate V1 or V2. I apologize for any confusion I have caused.


In any event the dry and reverb signal come together at the grid of the second 12ax7 triode.

[Diverted]

Pullshocks, I read that thread. I have a more recent version, with five filtering nodes.
One thing I noticed on previous schematics, and in your reply just now about reverb just being OK.
All schematics I saw show a 500K reverb pot. I reverse engineered the amp and traced out every component. The one I had, and the one I just built, has a 1M reverb pot and it can get very reverby!

Cool. Did you check the setting on the paraphrase phase inverter pot?
What are your plans for a low watt version?

[Diverted]

Pullshocks, I read that thread. I have a more recent version, with five filtering nodes.
One thing I noticed on previous schematics, and in your reply just now about reverb just being OK.
All schematics I saw show a 500K reverb pot. I reverse engineered the amp and traced out every component. The one I had, and the one I just built, has a 1M reverb pot and it can get very reverby!

Cool. Did you check the setting on the paraphrase phase inverter pot?
What are your plans for a low watt version?

I'm thinking about building a single ended version, yes! I really like that tone control and it's attractive to me to build a simple reverb with minimal parts. If Benson's doing it with just a 12AX7 for preamp, the one-tube reverb and a 6V6, confident I can do it without gain loss issues. I will play around with it.
I did check where the pot was set on the Benson weeks ago, but cannot for the life of me find my notes. I'm pretty sure it was less than 8K.

[roarshock]

Diverted, I've built a few single ended amps using Swart's/ Ampeg's capacitor coupled reverb. It feeds the reverb from the plate of the 12AU7 side of the 12DW7, instead of the cathode, like Benson's. I've used a it in a Magnatone 410 circuit, a 5F2a pre going intoa 12AU7, the pre-amp from a dual showman going into a 6V6 and a real funky Fanon Masco MA-11 conversion with tremolo and a 6L6.  I bet whatever you come up with sounds great.

[Diverted]

Thanks Roarshock. I've built probably five or six single ended units with standard Fender Reverb. It's just cumbersome though in those small amps — a simpler reverb really appeals to me.

[Willabe]

Thanks Roarshock. I've built probably five or six single ended units with standard Fender Reverb. It's just cumbersome though in those small amps — a simpler reverb really appeals to me.

No, the Swart/Ampeg he's talking about is 1 tube, capacitor coupled, no verb transformer. Very simple reverb circuit.

I own a Swart amp, it's PP 6V6, but it has the same verb circuit. The verbs very good, not quite as good as a full Fender transformer coupled verb, but very good, pretty close.

Came with a 2 spring medium decay, I put in a 3 spring long decay, much better. I use 3 spring tanks in any reverb I have.