Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tedsorvino1 on October 05, 2023, 02:51:00 am

Title: Ab 763 power amp section input.
Post by: tedsorvino1 on October 05, 2023, 02:51:00 am

Hi everyone.
i have a heavily modded blackface style Ab 763 (kt 66 power tubes, marshall style normal channel, vibrato mods, bkackface mod).
I would like to add a power amp section input for use with other preamplifiers.

I bet it can possible (even if it may be difficult).

But because i’m not very good on tube amplifier architecture (phase inverters, negative feedback etc.) even if i modded the amp myself - i would like to ask where and how should i place that power amp input.

Are there other users of such a mod and what the results are?

Thanks in advance.

Title: Re: Ab 763 power amp section input.
Post by: pdf64 on October 05, 2023, 04:43:54 am

A schematic of your heavily modded creation would be kinda helpful.

Title: Re: Ab 763 power amp section input.
Post by: tedsorvino1 on October 05, 2023, 04:54:04 am

Thanks for the reply. I haven’t got any special schematic. Just followed advice from this book
https://www.amazon.com/How-Hot-Rod-Your-Fender-ebook/dp/B004ZQG1T4

The original schematic was a common silverface twin reverb ( 6 pre tubes - 4 6l6 power tubes)  ab763 with heavily filtered rectifier and i transformed it to a common blackface (6 pre tubes - 2 kt 66 power tubes). Other than that all the info is described practically in the book, with any seriously detailed schenatics (marshall mod, vox mod, eq mod etc etc).

So any advice on the good old ab763 blackface twin would do.
I guess it goes before or after phase inversion. But i don’t kmow how.

Title: Re: Ab 763 power amp section input.
Post by: sluckey on October 05, 2023, 05:56:01 am

The power amp input is the left side of the .001µF cap.

Title: Re: Ab 763 power amp section input.
Post by: tedsorvino1 on October 05, 2023, 08:58:11 am

Thank you Sluckey. Exactly what i needed.