freestompboxes.org

Hello everyone,

I've been wanting to build a 6L6 amp for some time now and I've decided on the AB763 (Vibro-verb/lux) circuit. I thought I might go for a simplified circuit, though, for money and simplicity's sake. Anyways, my idea was to remove the Normal channel and the tremolo circuit. My guess would be that this will change the supply voltage to the preamp tubes and the bias voltage to the power tubes. Do I need to change some of the dropping resistor's values to account for this, or am I crying over spilled milk here?

Attached is the AB763 schematic with parts circled in red I figured I could leave out. Let me know if you see any blatant errors, I'm sure I've made some.

That'll probably work. You'd wanna take out the other 220K mixing resistor, that won't be needed. If your going for simplicity just do a princeton reverb and set it up for 6L6's and cut the vibrato off the bias feed. That amps already set up better for one channel use.

Hello JWP and Phibes,

I had the same idea and build a single channel blackface amp
with only the vibrato channel.
In my amp I build the reverb driver with a 5 watt chipamp
and the tremolo with 2 transistors.

Please leave the 220K mixing resistor in. Or better: make it 270k.
This way the preamp tube sees the same load as in a full amp.
Otherwise you'll get too much gain in the preamp which doesn't
sound good imho. Better put a 5K pot in series with the nfb resistor
coming from the speaker and call the the "raw control".

A nice way of voicing the amp is the following. As I did not have a
10pF capacitor to go parallel on the 3M3 resistor I made one myself.
Take two wires 25 cm long. Tightly twist them together.
Solder in place of the 10pF. Play the amp and listen. Untwist about
2 cm of wire. Repeat until satisfied. As a rule of thumb: 10cm of
twisted wire equals 10pF. Works like a charm!

My amp is build from scratch with a generic 320V PT and an OT from an old
PA amp. Solid state rectifier and 47K plate resistors in the phase inverter.
It's build in an old Evans solid state guitar amp and a Fender speaker of
unknown origin. Luckily I'm able to compare it with a real Fender blackface
2x 6L6 amp so I the know the sound of the original. And I'm very close
already.

Thanks for reading and succes!

Gait

Hello again,

Sorry if I wasn't clear about the 220K mixing resistor.
I made it 270K and put the free end of the 0.047 capacitor
to ground. That's how it works in my amp.

greetz,

Gait