Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: J Rindt on June 25, 2010, 06:25:38 pm

Title: Mating aa864 with ab165
Post by: J Rindt on June 25, 2010, 06:25:38 pm: What would be the best way to connect the AB165 preamp to the phase inverter of the AA864 power amp? Would I just come straight from Pin 6 of V2 to the 500pf cap of V4?
Thank You

http://www.el34world.com/charts/Schematics/fender/BASSMAN_AA864.pdf

http://www.el34world.com/charts/Schematics/fender/BASSMAN_AB165.pdf
Title: Re: Mating aa864 with ab165
Post by: FYL on June 25, 2010, 07:33:58 pm: Quote
What would be the best way to connect the AB165 preamp to the phase inverter of the AA864 power amp? Would I just come straight from Pin 6 of V2 to the 500pf cap of V4?

Yup. But I'd use a larger coupling cap, say 22n or more.
Title: Re: Mating aa864 with ab165
Post by: J Rindt on June 25, 2010, 07:56:55 pm: Quote from: FYL on June 25, 2010, 07:33:58 pm
Quote
What would be the best way to connect the AB165 preamp to the phase inverter of the AA864 power amp? Would I just come straight from Pin 6 of V2 to the 500pf cap of V4?

Yup. But I'd use a larger coupling cap, say 22n or more.

OK, I am just about ready to square this all up. I will change that cap to (correct me if I am wrong) .022 mics or higher.
Thanks
Title: Re: Mating aa864 with ab165
Post by: FYL on June 26, 2010, 06:09:29 am: Yes, 22n = 22 nF = 0.022 µF

1 nF = 1000 pF = 0.001 µF
Title: Re: Mating aa864 with ab165
Post by: J Rindt on June 27, 2010, 12:34:28 pm: I have only been doing this for a year or two, so it is possible I have made some fundamental mistakes. I am getting a couple hundred volts of positive DC on the pots of the Normal Channel.
With a speaker connected and the NFB connected, I get -23VDC on Pin 7 of V2, -4.2 on Pin 2 of V3, and -2.9 on Pin 2 of V4. If I disconnect the speaker or the NFB, the grids read normal.
Some of the B+ numbers also change drastically, depending on if I have a speaker plugged in or not.
I must have something wired wrong, but I cannot see what it is. I printed a layout and checked all my connections and components, but maybe I should do it again? The preamp is just kind of schizophrenic. I must have done something weird somewhere. There are no connections on the underside of the board, all connections are on top.
I took some pictures, just in case you guys see something obvious.
Thanks
(http://i111.photobucket.com/albums/n143/zzmoore/aa864andab165001.jpg)

(http://i111.photobucket.com/albums/n143/zzmoore/aa864andab165002.jpg)

(http://i111.photobucket.com/albums/n143/zzmoore/aa864andab165003.jpg)

(http://i111.photobucket.com/albums/n143/zzmoore/aa864andab165004.jpg)

(http://i111.photobucket.com/albums/n143/zzmoore/aa864andab165005.jpg)

(http://i111.photobucket.com/albums/n143/zzmoore/aa864andab165006.jpg)

(http://i111.photobucket.com/albums/n143/zzmoore/aa864andab165007.jpg)

(http://i111.photobucket.com/albums/n143/zzmoore/aa864andab165008.jpg)