NAD - J12 arrived!

[Jeff Haddad]

The Ampeg Jet J12 I bought from charliea here arrived in PA today. I made it feel right at home:

It sounds really good and it's nice and clean. Even has what appear to be original (1968) Ampeg-branded Sylvania 7591A's and also a couple Telefunken 12AX7's:

I'm curious if the speaker is ceramic or alnico but I didn't have the heart to take a screwdriver to it already to remove the magnet cover. Even though the amp is a '68, the speaker appears to have a 1966 date code - must be like all those millions of 1966 CTS pots Fender used for years

Thanks to charliea for a well-packed, quickly shipped amp!

 

[Jeff Haddad]

It's been kinda slow around here, so I thought I'd update this thread. The CTS speaker is alnico - I like how Ampeg used 12" speakers even in their "student" model amps. I'm going to try to open it up sometime to tweak the trem circuit - there's only a speed control with a fixed (very intense) depth. I want to tone it down a bit with a resistor change. I just need to find which resistor...

 

[Default]

Hey Jeff!
If you see that line on the schematic that goes from the trem section and feeds the two 270K resistors in the output tube circuit, you'll see that your Jet has a 680k resister to ground, while the R-12A has a 1meg pot to control intensity. If you have enough real estate in the chassis, I would just drill a hole and install a pot. If you don't feel like drilling extraneous holes, take one of the input jacks out and locate it there.

 

[Jeff Haddad]

My Jet schematic would be neither, it uses 12AX7 pre's. It's the J-12 Jet. But looking at the schematic, here:

It looks like there's 3 different resistors off the plate of the tube to ground, R31 and R32 (both 470k) and R36 (120k). My understanding is I want to go smaller value to lessen the intensity (or a pot of equal or lesser value), but I'm not sure which one. Sorry for the fuzzy image, it's the best I have except for a pdf which I couldn't post. I'm not the best at reading schematics!