Ab763 question

[spufuz]

Hi, im new here and this seems to be a nice forum!

I have a question about the Fender AB763-circuit.

Assume that i would build a Super Reverb based on the AB763 and want to exclude the Vibrato-channel, the vibrato-circuit and the reverb-circuit.
Meaning that i only want to build the Normal-channel stage and the power-stage.

Now take a look at the attached .PDF!

Would it be possible to simply exclude the circuitry that is not highlighted?
Or would it require major modifications in the circuit?

//David

[Structo]

Sure.
You could also use the unused half of the second 7025 as a boost stage.

[Gibsonman63]

You need to highlight your bias supply capacitor. It is part of the half wave rectifier for the bias supply. You can delete the highlight on the vibrato section and just use a 1.5K resistor and a 25/25 bypass capacitor where connector "A" is, since you probably won't have the preamp tube anyway for the non-existant vibrato channel.

Also, I am not sure if you need the 220K betwee the second section preamp and the phase inverter, but I would to research it. I would think you could reduce it to 100K since it is no longer in parallel with the other mixing resistor.

Just curious, why the Super Reverb with no reverb or vibrato? It seems that you could build a BF bassman and just use a SR output transformer if you want to drive 4 - 10s at 2 ohms. Or use a multi-tap output transformer and use any speaker you want.

[jaysg]

I think you still want the Reverb mix stage or something similar. The reverb versions seem to be more popular than the non-reverb versions, and that's the difference.

[Zippy]

Take a look at the topology description of Allen's "Old Flame":

http://allenamps.com/oldflame.php

"Design is loosely based on the mid 60's Fender Super Reverb™ but without a normal channel or a vibrato function. Design is enhanced with 3-knob reverb control, master volume control, "RAW" control, front panel power switches, impedence switch, and rear panel bias adjustment jacks."

Food for thought?

I used to play a black face Super Reverb - best sounds were in the "Vibrato" channel with the vibrato function neutered.

[spufuz]

You need to highlight your bias supply capacitor. It is part of the half wave rectifier for the bias supply. You can delete the highlight on the vibrato section and just use a 1.5K resistor and a 25/25 bypass capacitor where connector "A" is, since you probably won't have the preamp tube anyway for the non-existant vibrato channel.

Also, I am not sure if you need the 220K betwee the second section preamp and the phase inverter, but I would to research it. I would think you could reduce it to 100K since it is no longer in parallel with the other mixing resistor.

Just curious, why the Super Reverb with no reverb or vibrato? It seems that you could build a BF bassman and just use a SR output transformer if you want to drive 4 - 10s at 2 ohms. Or use a multi-tap output transformer and use any speaker you want.

Thats not a bad idea!
I really like the SR tone but a BF Bassman would maybe take me close to that? Its the AB165-circuit right?

The best sollution for me would be an output-transformer with an 4 ohm tap.

[Gibsonman63]

Four 8-ohm speakers in parallel gives you two ohms. I am not sure if that is part of the Super Reverb sound or not, but you could run four 8-ohm speakers in series-parallel for 8-ohms.

[spufuz]

To sum it up, im planning to build a single channel fender-based 40-50W tube amp.
The cab will be my parallel-wired 1960AX-cab. Wired for 4ohms.

[tubeswell]

Here's an idea

[Structo]

Here is the Allen Encore.

[M Fowler]

Encore layout

[drew]

I think one of the guys at the Hoffman forum prepared this; sorry, but I can't remember which one.

[spufuz]

Thanks for the tip!
I did a quick search, and found some threads about it!

I checked you attached schematic, and it seems to be exactly what im looking for! But the bias-circuit isnt there.
Is it possible to just use the original ab763 bias circuit?
And where does "A" go on your PDF?
Is any schematic or layout missing?

[KT66]

I agree with Jaysg that having the reverb mix stage is the much more popular option, and that most players use the vibrato channel. If you want the classic sound of this circuit ( Think SRV, Chris Isaak, early Eagles, Joe Walsh etc. etc. , I think this is the way to go).

This thread caught my eye because I have a 1 channel AB763 on the drawing board right now - no normal channel and no vibrato. Here is the layout and schematic I drew but haven't tested yet :

[M Fowler]

There is also Barry Witt's Princeton Reverb layout as well.