I need a power amp for a rack preamp to use for practice at home, but the lowest wattage i've found is the mesa or marshall 20 watt ones. so i looked up the schem for my epi valve junior and figured i could just mod it and put a jack between R5 and R15 so i could use the epi's power amp section for my rack preamp. do i have this correct? any components i have to add or will this work fine the way i was planning
what schematic are you working from? I've not got one to hand...
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
Here's an edited schematic but barring a few value changes its basically stock

I don't think you could make it into a power amp without some serious modifications but I don't know that much about power amps.
LTD F-50
Yamaha EG-112
'77 Harmony
Roadworn Starcaster
Gretsch G5120

Vypyr 15
Epiphone Valve Junior combo
Last edited by grungebaby at Aug 1, 2011,
here's the schem i have.

Stick a NC mono jack in there like you said and you should be good to go. wire it like so:

Using a NC jack lets you have normal operation with no plug inserted. Inserting a plug lifts the tip contact off the switch contact, breaking the preamp's connection to the power amp. This way whatever is plugged into the amp won't make it to the power amp along with whatever is plugged into the new jack.

Basically it's the same principle of wiring an external speaker jack to an amp.
No, like the one i linked to. The pic has the diagram. Tip means the hot connection. NC is for the little switch connection. Ring in the pic should say Sleeve and is the ground connection.