Adding reverb to tube amp: would this work?

[sean79]

I did some searching for how to add reverb to an existing tube amp. A lot of what I read seemed to involve adding tubes and "stuff" (I don't know much about amp building).

A guy I work with (he used to work on amps) told me that adding reverb shouldn't have to be too hard. From what I remember about the conversation, he said something like, "You don't have to add any tubes. You can just run a new [something] from the preamp, and run it down to a spring reverb unit. Then, you just run it back into the [something]." I guess I don't remember the details.

So... if a person had a mid-60s tube amp without reverb, is the operation as simple as he made it sound to me, or is there a lot more to it?

 

[mlove3]

There are several ways to accomplish this, but you won't get the same results as an amp with built in reberb without adding circuitry. IMO not worth modding an amp, too expensive, just buy a different amp.
If your amp has an fx loop you can run a reverb unit that way although most amps have a series loop, not parallel, and that'd be the preferred method to get a true fender style reverb, blending the dry with the "wet" effected signal.
Clarify what his solution is and try it, sounds to me like he's telling you to run it front end, which may be ok.

 

[sean79]

I'm not sure what "run it front end" means, but I'll ask him for some clarification. Thanks.

 

[Tim Armstrong]

I believe he means using an outboard reverb in front of the amp. I used to play through an SF Bassman head or a non-reverb Princeton Amp and that worked quite well for me. Sounds to me like the guy you were talking to was suggesting putting in a passive effects loop and plugging an outboard reverb unit in that way...

Tim

 

[mlove3]

sorry, let me clarify, running it front end is what Tim said. installing a passive fx loop is ok but I'm not a big fan of that approach. Even if it's done by a good qualified tech you're talking a few $$ and the overall tone is only as good as the quality of the reverb unit, not to mention you'd need to mindful of signal levels. If this guy you know really understands tube amps he could something custom for the particular reverb unit in mind.
I prefer a parallel fx loop, which is typically how fender and other amp makers insert reverb.
Why not just buy an amp with reverb and sell the old one?

 

[laird]

The short answer is that there's more to it. The simplest method is to add reverb to the signal before it reaches the amp. This can be done with a reverb pedal (cheap) or a standalone reverb unit (expensive). Weber makes a sneaky little unit that can hide inside most combo amps, they call it the Add-a-Verb.

If you're recording, or playing live and mic'd into a mixer, you could have reverb added at the soundboard, after the amp.

There aren't that many amps that have an effects loop but no reverb, but even if you have one of those, you still need a pedal or standalone 'verb unit to do the work.

Adding reverb within the amp takes 3 pieces: A small power amplifier to drive the spring reverb tank, the tank itself, and a signal amplifier to boost the reverb signal back up and mix it into the main signal. A typical old fender amp will use a 12AT7 tube and a small output transformer as the power amplifier, and a 12AX7 as the signal amp & mixer. It's usually tough to make room for the components if the amp wasn't originally designed to house them. It can be done, but it's quite a project!

-Laird

 

[sean79]

Thanks, everyone. That little Weber add on unit is $300.

Why not just buy an amp with reverb and sell the old one?

Well, I guess I'm not really hell bent on getting this mod done... just doing some initial poking around to see what would be involved at this point. The amp in question is a mid-60s Guild - it cost me $0 so far. I've thought about building a new cabinet for it, and I could make sure there was room for the extra reverb stuff.

Reverb is cool. If it's not really doable, I'll probably just keep the amp sans reverb. I already have another tube amp with built-in reverb. Appreciate the replies/suggestions - I'm trying to learn.

 

[Larry F]

I have a Fender reverb unit that I use all the time. When I don't want to lug it around, I use a Hermida (sp?) reverb pedal that cost $100. I only mention this pedal because of it very high quality of reverb sound.

 

[bradpdx]

For the all fuss and bother, I'd stick with any one of the really decent external reverb pedals and just treat it like any other effect.

The real Fender reverb circuits, as described in this thread, are a bit much to implement as aftermarket.

 

[M Fowler]

If you have half of one triode left then all you have to do is add another 12AX7 socket, two RCA jacks, Hammond 1750 reverb driver, Accutronics 8AB2A1B, short tank, medium delay (I like the best) and 100KB pot. Take a look at the Matchless Lightning for how its done. The reverb is brought back to the bottom of the PI rather then to input of PI.

Get ahold of me and I can help you out.

Mark

 

[sean79]

Thanks, Mark. I'll have to look into whether or not I have half of one triode left. The amp has two 12AX7s for the preamp, two 6GW8s for the power, and the 6CA4 for the rectifier. Will the schematic tell me if I have half a triode left? I'll do a search on the Matchless Lightning.

 

[M Fowler]

If there are two channels (two volume controls) then I would guess your using both halves of that first 12AX7 and the second 12AX7 as the phase inverter.

So it would require additional tubes which brings up a potential problem when adding tubes. Whether the total amperage of the 6.3V tap is at its limit. Many power transformers are over rated which allows addition of extra tubes but not sure in your case. Adding one tube verses two can make or break this mod.

Many amps can easily have reverb added and others not as easy. How do you like the sound of the 6GW8s power tubes?

 

[robt57]

Sometimes a quick slapback delay will add enough verb to the sound. I know when I use my Boss DD-5 I kick off the amps reverb, the tow are too much for low gain setting IMO.

 

[sean79]

If you have half of one triode left then all you have to do is add another 12AX7 socket, two RCA jacks, Hammond 1750 reverb driver, Accutronics 8AB2A1B, short tank, medium delay (I like the best) and 100KB pot. Take a look at the Matchless Lightning for how its done. The reverb is brought back to the bottom of the PI rather then to input of PI.

I looked at the tube sockets for those 12AX7s - all lugs have something wired to them. Does that mean I can't have half of one triode left?

If there are two channels (two volume controls) then I would guess your using both halves of that first 12AX7 and the second 12AX7 as the phase inverter.

I have one volume control on the amp (pull for "bright"), a tremolo speed control, a bass control, and a treble control.

Can my wire out to the reverb share a power out wire from one of the 12AX7s in the preamp?

As for the sound of the 6GW8s... I'm not sure yet. I got the amp used, and it's still in need of repair. I've got a couple (maybe three) new 6GW8s on the way, and I'm going to check out all my caps and resistors. I'm looking forward to getting it up and running.

 

[M Fowler]

I doubt if you have 1/2 of the triode left in that amp. There is a one tube reverb that has the mix and recovery that can be a retro fit but if you don't know how to work on the circuits it would be hard for you to do. Even newbies can do a retro fit but you have to know how your circuit functions first.

I would get the amp up and running and see how it sounds first. By using a good speaker like my Celestion Alnico will make an amp sound good. I love tube reverb but I also have a Boss reverb pedal if its an amp that I don't want to change over like my Trainwreck Liverpool Clone.

Mark

 

[Greg.Coal]

The short answer is that there's more to it. The simplest method is to add reverb to the signal before it reaches the amp. This can be done with a reverb pedal (cheap) or a standalone reverb unit (expensive). ............ [snip]

-Laird

Everything in Laird's post was accurate and excellent. Other comments about parallel versus series are correct, too. Those mentioning ".. it's not worth it .." don't seem to have gotten your attention too much at this point but they are correct as well. That's because we've all gone down this road, making modifications of varying success but ultimately ending in a larger investment in an amp that we hadn't really intended and that exceeds its value.

A pedal reverb is "good enough" and inexpensive; being modular, it can be used on other amps, or swapped for diff reverb or echo pedals; or sold. Rather than mess with your Guild, don't you feel an obligation to buy another amp? It would be doing the world economy a big favor.

Also, to add to the complication, comparing the cost of the mod to the many excellent values in used gear -- you'll not only get reverb but another amp with its unique characteristics and but also greatly increase your happiness.

Greg

 

[Commodore 64]

Someone I know added it to a Valve Jr, using a Belton Module.

This is his Schematic. He got the 5v from a 12AX7. I'd like to figure out something liek this for my Pathfinder.

image removed

He was initially unhappy with the sharp and brash nature of the reverb, but added that 100k resistor seemed to alleviate it.

used a 100k resistor between the block and one of the connections on the main circuit board and took the splash out and smoothed it out - pretty happy with it now

 

[diggert]

Add reverb to a 5e3

The short answer is that there's more to it. The simplest method is to add reverb to the signal before it reaches the amp. This can be done with a reverb pedal (cheap) or a standalone reverb unit (expensive). Weber makes a sneaky little unit that can hide inside most combo amps, they call it the Add-a-Verb.

If you're recording, or playing live and mic'd into a mixer, you could have reverb added at the soundboard, after the amp.

There aren't that many amps that have an effects loop but no reverb, but even if you have one of those, you still need a pedal or standalone 'verb unit to do the work.

Adding reverb within the amp takes 3 pieces: A small power amplifier to drive the spring reverb tank, the tank itself, and a signal amplifier to boost the reverb signal back up and mix it into the main signal. A typical old fender amp will use a 12AT7 tube and a small output transformer as the power amplifier, and a 12AX7 as the signal amp & mixer. It's usually tough to make room for the components if the amp wasn't originally designed to house them. It can be done, but it's quite a project!

-Laird

Laird I would like to add tube reverb to my 5e3 clone I dont care how involved it is I've seen It added on the inside of the cab but without a layout I'm lost . Thanks Digger T.

 

[BobbyZ]

Welcome to the forum Diggert.
I would recomend a pedal like the Holy Grail or an old Fender Reverb unit or clone.
I'm just thinking in terms of money and the pain in the butt factor of adding it to an amp. A stand alone reverb or pedal will work with any amp you may have.
I'm sure it can be done however if you want to go that route.

 

[celeste]

To add a tube driven and recovered reverb like Fender uses, you will need to add a driver tube, usually both halves of a 12AT7, a driver transformer (like an OT for the reverb) and a recovery tube, usually 1/2 of a 12ax7 (could be a 6AV6). That would require another 600ma of heater current, and about 25ma of B+ current. If you don't have the current to spare from your existing PT, they you will need to change the PT as well.

If your current build is in a stock 5E3 chassis, then you are going to have problems finding room for it all. If you went with a medium impedance tank instead of the low impedance tank fender uses, you could do away with the reverb transformer and configure your driver tube as an SSRP. The current requirements would be about half the B+ and the same heater.

If you can not find the room for even 2 tubes, you could go with a high impedance tank and drive it SS. That would require a low voltage power supply, but all the drive circuitry and power supply could be out of the amp chassis and down with the tank. Recover it with a tube. Current requirements from your existing PT would be 300ma heater and 1-2ma B+.