Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Big_Mike on July 14, 2026, 06:09:48 pm

Title: Vox AC15 based on Hoffman AC30 layout
Post by: Big_Mike on July 14, 2026, 06:09:48 pm: Hi guys,

I am gathering materials to build an AC15 from a Hoffman AC30 layout. I get that you simply remove two of the output tubes and increase the cathode resistor, but I would like some help modifying the Hoffman layout as follows:

1. Change from tube rectification to solid state rectification.

2. Add in a Lar-Mar PPIMV.

Could anyone help me with modification of the Hoffman layout? Thanks.
Title: Re: Vox AC15 based on Hoffman AC30 layout
Post by: passaloutre on July 14, 2026, 09:05:46 pm: Neither of those requires a change to the layout. You can put a rectifier on a couple terminal strips, and the LarMar is built on the pot.
Title: Re: Vox AC15 based on Hoffman AC30 layout
Post by: Big_Mike on July 14, 2026, 09:31:07 pm: I guess what I am trying to figure out is how to incorporate diodes for the solid state rectifier on the board layout. I think I figured out the wiring points for the Lar/Mar PPIMV. Could anyone help me with a turret board layout diagram for a solid state rectifier?
Title: Re: Vox AC15 based on Hoffman AC30 layout
Post by: sluckey on July 15, 2026, 09:24:58 am: If I were using Hoffman's board I would just replace the two 100Ω filament resistors with two 1N5408 diodes and make a couple minor wiring changes. Like this...
Title: Re: Vox AC15 based on Hoffman AC30 layout
Post by: Big_Mike on July 16, 2026, 10:25:22 pm: Quote from: sluckey on July 15, 2026, 09:24:58 am
If I were using Hoffman's board I would just replace the two 100Ω filament resistors with two 1N5408 diodes and make a couple minor wiring changes. Like this...

Thanks Sluckey, much appreciated!
Title: Re: Vox AC15 based on Hoffman AC30 layout
Post by: Big_Mike on July 23, 2026, 04:28:54 pm: Sluckey, to install a Lar/Mar PPIMV, I assume you remove the two 220K resistors after the phase inverter and install a dual gang 250K pot? Thanks!

Mike
Title: Re: Vox AC15 based on Hoffman AC30 layout
Post by: sluckey on July 23, 2026, 05:26:43 pm: Yes . Also put a 2.2m between wiper and ground lug of each pot for safety. If you will also have a cut pot then look at page 3 of this pdf to see a neat way to install the mv...

https://sluckeyamps.com/dual_lite/dual_lite.pdf
Title: Re: Vox AC15 based on Hoffman AC30 layout
Post by: Big_Mike on July 23, 2026, 06:25:04 pm: Quote from: sluckey on July 23, 2026, 05:26:43 pm
Yes . Also put a 2.2m between wiper and ground lug of each pot for safety. If you will also have a cut pot then look at page 3 of this pdf to see a neat way to install the mv...
https://sluckeyamps.com/dual_lite/dual_lite.pdf

Cool, I was wondering how to incorporate a cut pot with a Lar/Mar master and plan to have it with this amp. Thanks for the info!