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previous: John Forman First off, thanks Doc & Mark for th... -- 5/11/2000 9:46 PM View Thread

Re: SF Princeton Pull Boost removal

5/12/2000 1:56 PM
Re: SF Princeton Pull Boost removal
Only glad to help out.  
>>I would love to install a standby switch there instead of the ground switch. Where can I get the info?  
I put a SPST switch in after the first filter cap and before the OT plates. Look at the schemo's of other Fender amps and you'll get the idea. Get one that's rated for the high voltages here.  
>>I did not realize that the reverb circuit in this amp is different from a plain SFPR. I will have to look that over more.  
Yep! Trace the schemos and compare voltages, and you shall see the diffs.  
>>I am also looking at cap changes to get rid of the fartyness that this amp clearly has. To me it sounds great at low volumes, but cant take the bass when turned up.  
There's some ampager guyrus who know this amp inside out and upside down who advocate changing the coupling cap to the phase inverter from the stock .02 value to a quarter of its value. I put in a .0047 O'drop and it cleared up some of the bass response a tad. IME, you can get mo' tighter bass with a high quality speaker and by swapping the OPT with the bigger one used in the Deluxe. I got new one for under $30 from Ampwares and it fit right in using the extra mounting hole predrilled at the factory. With my 50W Eminence speaker and this bigger tranny, the bass really thumps now.  
>>Any tips on biasing this amp? I still have the original tubes in it.  
Got myself a Swamp Probe and a digital multimeter, and installed a bias adjusment pot in the pull-boost foot pedal jack which was no longer used. Ran some leads to the pot from the bias circuit board and now biasing is a breeze. You don't want the pot to be tampered or adjusted inadvertently so I didn't put a knob on it and shaved down the shaft to make it less vulnerable.  
Sounds like you could use a new set of tubes too, unless the amp wasn't used much. The JAN Philips 6V6 in mine are nice (running at 24ma) and there's some good feedback on the new Sovteks (I forget the suffix).  
Good luck!