Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: clayman on June 18, 2011, 09:18:24 am

Title: pro jr.
Post by: clayman on June 18, 2011, 09:18:24 am

A friend gave me a pro jr.that only needed minor work. How can I tweak it for more gain? Or should I just leave it and use a box.

Title: Re: pro jr.
Post by: RicharD on June 18, 2011, 09:27:38 am

Where's the schematic?

Title: Re: pro jr.
Post by: clayman on June 18, 2011, 09:58:07 am

it is in the library,I dont know how to move it to the forum,computer dummy.

Title: Re: pro jr.
Post by: clayman on June 18, 2011, 10:06:22 am

first thing I see is that there are'nt any bypass caps on the 12ax7 cathodes.

Title: Re: pro jr.
Post by: RicharD on June 18, 2011, 10:22:26 am

I don't even know who makes the Pro Jr.  If there are no cathode bypass caps, adding them will certainly increase gain.  Clip leads are your friend in this instance.  If it has a global NFB loop, lessen the amount of feedback.  What sorta tone stack does it have?  How are the preamp tubes loaded?  You could probably put a tone stack bypass switch in and get more gain.  If the preamp tubes are heavily loaded (like 100k) then you could try lessening the load with a 500k or 1M.

Title: Re: pro jr.
Post by: VMS on June 18, 2011, 10:29:22 am

Schematic:

http://support.fender.com/schematics/guitar_amplifiers/Pro_Junior_schematic.pdf (http://support.fender.com/schematics/guitar_amplifiers/Pro_Junior_schematic.pdf)