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surfpup

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Worked on my old 69 Princeton some today... I snipped that pesky negative feedback loop. Also re-tubed and swapped the 5U4G rectifier tube for the GZ34/5AR4 that the tube chart specs... Sounds pretty good now!

 

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The guts...

 

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Not sure why you got a minus so I plussed you back up :rolleyes:

 

Looks really original in there huh? Does the omittion of the NFB bring the dirt up to par with the reverb models? Might be a neat thing to put on a switch. Maybe repurpose the ground switch?

 

Yeah man, it's funky in there - spider webs even. [scared]

 

The NFB switch is definitely a cool mod that some people do in old Fender amps. Works great in Bassman heads for example. But it this case the NFB loop definitely does not bring it up to par with the Princeton Reverb as far as gain/grit because the reverb model has an extra 12 AX7 pre-amp tube - half of which goes to the reverb return and half of which is used to add more gain.

 

My Princeton Reverb has a lot more gain/grit than this non reverb one. This one stays clean all the way to ten (though a little less so now). [biggrin] As such I don't see ever wanting to switch the NFB back in. [thumbup]

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Ooohh nice!

 

Those white Mallory cathode bypass caps should probably get replaced. That'll help keep the low end intact. Maybe the bias cap too if it's old. [thumbup]

 

Has the cap can ever been replaced?

 

Oh, and you can put a 5 or 10k pot where the external spkr jack is to adjust the nfb loop from the normal resistance (2.7k?) up to say 2.7 + (5 or 10) = 7.7k to 12.7k. 7.7k will sound pretty much like as if you snipped the circuit out all together. You could try a 5k and 10k resistor in there to see what range you need before installing a pot.

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Ooohh nice!

 

Those white Mallory cathode bypass caps should probably get replaced. That'll help keep the low end intact. Maybe the bias cap too if it's old. [thumbup]

 

Has the cap can ever been replaced?

 

As far as I know everything is all original. It's pretty quiet for an amp full of old caps. Quieter than my Deluxe Reverb. The pots crackle, but that's it. I'm sure it could use a going over.

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