Board-mounted-tube module Champ Reverb build

[tdvt]

 I have been chipping away on this tube module project for several months, as time allows, & powered  it up just today.

 I originally started out down this path, building an add-on tube board based on Tubenit's one-tube reverb, for an existing 5F2A I built a few years ago.
But I then thought about breaking out all the various sections of an AB763 & designing board-mounted tube modules for each section. (I never installed the one-tube as I got side-tracked with the bigger project)

 
So this is kind of an experimental first try to see how well the module concept might or might not work.

 
In order not to get too complex for a first try, the circuit is a Champ with 2-tube reverb. I had drawn up the circuit I wanted but then found an existing schematic (Tubenit's I think?) of nearly the exact same thing, so I used that.

 
The two modules I used in this one are a  AB763 TMB pre-amp & the AB763 2-tube reverb. The 6V6 is chassis mounted. The only deviation from that schematic is the SS rectifier & I added an extra B+ node on the front of the power rail, utilizing a choke. The 9-pin tube sockets are mounted directly to the FR4 boards, the various components are then mounted on turrets surrounding the socket & jumpers/buss wire/control wires link everything together.


I used a chassis I had on-hand & while everything fit, a little more space would have been nice, as would have been including tremolo.


The amp made sound after the light bulb limiter test, but had pretty significant hum & some oscillation as the volume & treble pots were swept near top rotation.

 
I traced the hum to the heaters (6V battery test) & was leaning towards the idea not really being practical, thinking there might be some proximity or lead-dress issues, though with the board-mounted sockets, some things are not tweak-able. But while pondering the problems, I realized I had not installed the artifical heater center tap.

I installed that & ALL of the issues disappeared, including the oscillation. Things are now pretty quiet, in a good way...

There is still a small amount of noise at the very, very top of the volume control sweep but I haven't gotten back to it yet to try to deal with that. But otherwise the amp sounds pretty good & the controls all function as expected. Reverb is surf-drippy,  even with a short pan (3-spring & dwell control)

 

[sluckey]

Nice job!

[tdvt]

Thanks!

I wouldn't build everything this way, but knowing that the module idea is viable, I will fool with refining it & trying it out on a couple other builds.

Given the chance to start over, there are any number of things I would change on this one,  but just trying it out was the point.

[tdvt]

I thought I would update this project as it has taken a few twists over the last weeks.


Long story short, I had intended this amp to be a small head & built a cabinet to that end. But with a reverb tank in such a small box, the tank was picking up noise creating a hum in the reverb circuit that I could not get rid of. The amp was otherwise very quiet.

So I decided to make it  a combo, in order to have more options & distance for mounting the tank.

Unrelated, while looking for Supro trem info, I had seen the retro-design vertical-chassis amps that @Bash had built & had saved some pics as I thought they were pretty cool.

As in turned out, the small chassis of this amp lent itself to the vertical chassis & kept the package wider than taller.


The staggered knobs were total coincidence, but are definitely part of the look of the Silvertone 1482, which is probably the most known vertical-chassis amp.


Should button it up tomorrow. 

[dogburn]

Nice! A Champ with Reverb would be an awesome amp for home use. But I'm not clear which Champ circuit you are basing it on - is it 5F1 or AA764?

[tdvt]

It is basically a AA764 with the AB763 2-tube reverb added, as well as a choke & extra B+ node. SS rectification.

The 2-tube reverb adds a third mixing gain stage before the power tube.

Controls are Vol, Tr, Mid, Bass, Dwell, Reverb

I am using a MOD 3-spring short tank

Pretty much the schematic above, w/minor changes

[dogburn]

Sounds like an awesome amp overall. And the cabinet and vertical chassis arrangement look great!

[jjasilli]