Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Bubbastain on April 17, 2018, 06:17:29 pm

Title: Sound City 50 pa Plus power amp in.
Post by: Bubbastain on April 17, 2018, 06:17:29 pm

My Sound City 50 PA Plus is working great and sounds really good and I have been using it as a pedal platform amp with great results. One thing I would like to ad would be a power amp in jack. Ideally I’d like to have it between the preamp section and before the amps master volume control. The main distortion pedal I have on my board is an AMT R2 which can be used as a distortion pedal or a preamp. I’d like to be able to bypass the amps preamp section and use it as a power amp only. Would this be pretty simple? I’m just a paint by numbers fiddler, but I’ve been successful doing repairs and mods with help from others and I am careful to not shock myself.

I believe this is the schematic

http://el34world.com/charts/Schematics/files/soundcity/soundcity50plus.pdf

https://i.imgur.com/MMCCXcz.jpg

Title: Re: Sound City 50 pa Plus power amp in.
Post by: sluckey on April 17, 2018, 07:20:48 pm

I would mount a 1/4" phone jack near V3. Then connect a .047µF cap between the jack tip and V3 pin 6.

Or, mount a 1/4" phone jack near V4. Then connect a .047µF cap between the jack tip and V4 pin 2.

Title: Re: Sound City 50 pa Plus power amp in.
Post by: Bubbastain on April 17, 2018, 09:58:36 pm

Thanks! I’ll see if I can get that cap and decipher where exactly those spots are.

Title: Re: Sound City 50 pa Plus power amp in.
Post by: chocopower on April 18, 2018, 06:55:44 am

The schemstic you posyed is for the guitar version.
yours is the PA one. there are no schema for that one (i searched for it years ago).
maybe the power amp and p.i. are the same...


In yours, one good spot to enter to the power amp will be the top of the master volumen.