Tube reverb build project

[mountainhick]

A little different experiment, a simple point to point tube reverb to use on any amp with FX loop.

I was playing around with a smaller chassis, but with the power transformer cutout, things were tight. I just freed this chassis from an old magnavox hifi amp, it is too small for my intended project for its guts, and will re-task the tubes, sockets and transformers into a Deluxe in a different chassis.

This is large for the project at hand as is, but if I want to later there's room to make it into a 2 tube reverb and/or add tremolo for a re-vibe kind of thing.

The top was a huge mess of holes. I cut out the top leaving a rim of metal around the edge and spot welded a new top in from the inside.

Next, smooth off a couple spots where the welds went deep, and drill/cut holes...

 

[chas.wahl]

Circuit?

 

[mountainhick]

Circuit?

Essentially Tubenit's single tube circuit to start. Experimental in terms of an outboard rig so will probably mess with various component values. If it isn't enough, I have a 6F3P (ECL82) to try, and if still unsatisfied, a fender 2 tube version a la Princeton reverb etc. 12AT7 and 12ax7 triode. If the Tubenit version works out, that would be great!

I'll post it as that work comes around. My layout will be different. Right now drilling cutting holes, Bondo for the gaps under the welded new top. I think it'll be ready to paint tomorrow, then circuit starting Monday. Should be just a few days to get it working.

 

[mountainhick]

Circuit?

Here. from a previous thread:

 

[tubedude]

Not the best circuit for reverb. Search for current drive reverb circuits. Better dynamics and better frequency response. A typical 10 Ohm tank (@1kHz) will have an impedance 30 times that at high frequencies. Driving a coil with a voltage source will be hard to get strong signal at treble frequencies, especially with one triode.

 

[mountainhick]

Not the best circuit for reverb. Search for current drive reverb circuits. Better dynamics and better frequency response. A typical 10 Ohm tank (@1kHz) will have an impedance 30 times that at high frequencies. Driving a coil with a voltage source will be hard to get strong signal at treble frequencies, especially with one triode.

Much appreciated. I do get that. I am not after huge wet dripping surfy verb. I only use a little in the background. I'll give this a try. I have the 6F3B and 12AT7s and 12au7s as well, so might go through some variations. I enjoy the experimenting.

@tubeswell seems to like a variation on the tubenit version with different component values. Calls it lush for 12ax7:

 

[tubedude]

Much appreciated. I do get that. I am not after huge wet dripping surfy verb. I only use a little in the background. I'll give this a try. I have the 6F3B and 12AT7s and 12au7s as well, so might go through some variations. I enjoy the experimenting.

@tubeswell seems to like a variation on the tubenit version with different component values. Calls it lush for 12ax7:

I hear ya. I like very little reverb myself. Every factory amp seems built for surf music. I always end up with touchy controls, going from minimal just right, to overwhelming in less than a millimeter of travel.

 

[mountainhick]

I got slowed down by analysis paralysis, but came up with some good thoughts and I think good decision (Still uncertain but kind of why not?) , and possible future considerations There are still theoretical questions (in Bold):

1- The PT I am using doesn't produce 400VDC like a lot of reverb circuit drivers use. I am a little concerned about the lower voltage, and think that avoiding a lot of voltage drop from power filtering would be undesirable for this circuit. I am also concerned about noise. I am also a little confused why some reverb circuits use minimally filtered B+ from the power tube node for the transformer/tank driver?

Anyway, why not filter that first supply node on this project... with a choke? I remembered that I have a choke from a radio I disassembled, checked it out, it reads 3.5 Henries, and it supplied the entire radio including a SE 6V6, so current wise, should be just fine. resistance is a paltry 306 ohm:

LC Ripple Filter Calculator

www.ampbooks.com

39db attenuation
0.4 VDC drop

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www.digikey.ca

3.5H, 47uf LC filter, -3db at 12.4Hz... Is this low enough? Should I parallel 2 47ufs?


2- In researching grounding of send/return jacks to the tank, I found that my Mesa Boogie uses a one tube reverb, essentially the same config as my project. I have this in one of my amps, a Mark IV, and I like this reverb. But it uses a 12AT7... more current. so I'll build for the 12AX7 but have that 12AT7 scheme as first backup before going to a pentode or two tube reverb scheme.

3- Also looking into super simple tremolos for a potential add on in this box. Things can get way not simple with harmonic trems and such, but Uncle doug's tremoverb based on a Supro desing uses a one tube arrangement. To make this work in my project I would have to use it for the cathode of a gain stage. I am wondering if that could be the reverb's recovery triode, or if I would have to add another gain/output stage? EDIT: I think I reasoned my own answer on this one. The reverb signal is mixed with dry signal, so this would work only on the amount going through the reverb itself, not the full trem effect on the whole enchilada. Probably not as desirable in terms of depth of the effect. And it would mean reverb would have to be on for trem to work, which would be fine for me personally since I don't switch reverb off, I just use a little all the time. I think my solution would be to go full Fender style reverb with parallel 12AT7 and one 12ax7 triode recovery, and run the recombined signal (dry plus reverb) through the orphaned 12ax7 triode in the tube with the reverb return.

 

[mountainhick]

Progress, almost completely drilled for version 1, and primed. I need to pick up some top coat , maybe hammertone.

 

[mountainhick]

It's working. startup went 100%, everything works. Noise free. All I have are 15' cables, so there is a lot of loss with 30'. Sounds lossy and muddy. I am making a couple shorter cables.

I put in a pot for the straight through signal. In different amps this resistor value varies wildly. With full 1M, all you hear is reverb, no dry signal. I'll adjust this to taste and wire a fixed value. Making new short cables

Then, tweak time.

EDIT: Oh heck! Pictures can bring things into focus. I have that extra pot wired on the wrong side of the output resistor... first tweak done.

My first point to point, so far not a great fan. There must be a heap of assembly tweaks that I don't know yet that make it easier. I am going to build a wreck knock off point to point. That will make or break any passion for it!