Preamp Bias vary Trem in AB763?

[guitylerham]

Howdy,

Tinkering on an AB763 build I finished last year and wanted to know if a vibrochamp style bias-vary Trem (preamp cathode wiggler) could be implemented at the cathode of the last stage, V3b, before the phase inverter. I’m using power scaling and don’t want to put the Trem on the output tubes because I won’t be able to proportionately scale the Trem voltage as I scale the output section.

Here’s the schematic for an AB763: https://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf 

Anyone ever try this?
Thanks!

[Willabe]

I’m using power scaling and don’t want to put the Trem on the output tubes because I won’t be able to proportionately scale the Trem voltage as I scale the output section.

Kevin has a kit for that.

[guitylerham]

I’m using power scaling and don’t want to put the Trem on the output tubes because I won’t be able to proportionately scale the Trem voltage as I scale the output section.

Kevin has a kit for that.

Yeaaah, I didn’t order it like I should have and now want to try and figure out an alternative. My amp can go from fixed to cathode biased output tubes so a tremolo that works on a preamp tube would be best. Just brainstorming alternatives. Thanks for the heads up!

[sluckey]

Before you commit to the VC style trem take a look at this thread...

    http://el34world.com/Forum/index.php?topic=24334.0

This tremolo circuit is implemented exactly like a real AB763 trem, but it produces a stronger, smoother trem than the AB763 neon bulb roach or the bias vary trem that Hoffman put in his modified AB763. This doesn't vary any bias so it doesn't have the issues that bias vary trems may have. It simply shunts the guitar signal to ground at the trem speed. So you can power scale anything you like ***EXCEPT*** the tremolo oscillator.

This has been successfully installed in quite a few amps including a Pro Reverb, Bandmaster, and Princeton Reverb. Everyone has been very pleased. You will find schematics showing exactly how it was connected in the Fender amps I just mentioned.

Anyhow, worth reading even if you don't want to use it.

[guitylerham]

Before you commit to the VC style trem take a look at this thread...

    http://el34world.com/Forum/index.php?topic=24334.0

This tremolo circuit is implemented exactly like a real AB763 trem, but it produces a stronger, smoother trem than the AB763 neon bulb roach or the bias vary trem that Hoffman put in his modified AB763. This doesn't vary any bias so it doesn't have the issues that bias vary trems may have. It simply shunts the guitar signal to ground at the trem speed. So you can power scale anything you like ***EXCEPT*** the tremolo oscillator.

This has been successfully installed in quite a few amps including a Pro Reverb, Bandmaster, and Princeton Reverb. Everyone has been very pleased. You will find schematics showing exactly how it was connected in the Fender amps I just mentioned.

Anyhow, worth reading even if you don't want to use it.

Hey there, that looks pretty damn cool. I’d be happy to have a solid Trem even if it’s not the holy bias vary type. I’ll mock that up tonight and get back with my thoughts.

MUCH appreciated!

*will need to order a vtl5c1 first! ;)

[sluckey]

Get a 50K-RA pot too, unless you happen to have one laying around. AES has both parts.

Please post your results in this thread and also the "More Trem" thread if you don't mind. I really think you'll never look back at the bias vary trem after you play with this a bit.

[shooter]

50K-RA

for int, or speed

thanks

[sluckey]

INT

[guitylerham]

Get a 50K-RA pot too, unless you happen to have one laying around. AES has both parts.

Please post your results in this thread and also the "More Trem" thread if you don't mind. I really think you'll never look back at the bias vary trem after you play with this a bit.

I will do that as soon as I make the changes! Thank you.

[guitylerham]

I finally got around to opening this amp back up and installed this trem circuit. It works great and doesn’t have the thumping. I think it’s deep enough but I also didn’t check the resistance of all my optos to see if it was average or not. I’ll be including this in another build as well. Thanks again, Sluckey and everyone else for this great addition!