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Amp post: ampeg jet
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SuperBee
3986 posts
Aug 13, 2016
5:11 PM
Whatever is all the buzz with apps and recording software and pedals and lightweight reliable kit that makes life easier, I still like old amps. Maybe it's like how people like steam power.
I know it's old hat. But I like it.
I know I'm not alone, even on this forum, rather than a dedicated old amp electronics forum.
Anyway, my latest is an ampeg Jet J12 B

This is an early 60s amp. It was once anyway.
The only original parts are cab, chassis, transformers, handle, and perhaps the pots and switch, knobs, eyelet board, valve sockets.
I don't think there is any original wiring outside the transformers. Certainly there are no original caps or resistors.
Which is nice in a way. There is no chance of reducing the 'collectible' value. It's just an old amp that still works.
As long as I don't blow up a transformer.
I obtained it through a swap deal. No doubt I lost money on the deal but I'd already lost that money in a way.
So, the amp:
It's a push pull, cathode biased power section originally designed for a pair of 6V6 tubes and rated at 12 watts. It is now running a pair of 5881 tubes, which are essentially 6L6 with a different name.
The preamp uses a 6SL7, as does the phase inverter.
The PI had been modified to deliver more gain. I changed it back to original spec.
The amp also has s tremolo circuit, which uses the other half of the preamp tube. It's a very basic tremolo with only s speed control. It had been set up for a footswitch but I completely rebuilt it back to the circuit shown in the schematic. At some time in the future I might go back to the footswitch idea but the amp had so much in the way of 'tacked on' mods, I felt I needed to start again in a few places. Having completely rebuilt the preamp, trem and PI, I now think I should actually strip it and start all over as I have a much better idea of how to lay it out. I'm sure I can do better now.
But it 'works' and I have other priorities, so it can stay as is for a while.

But how does it sound?
I'm seriously considering selling my silverface Princeton Reverb.
This amp was intended for much the same market as the Princeton. It's a practice amp, bigger than a champ, maybe you can jam with friends. It's not really a stage amp but definitely louder than the champ type amps. A 12" speaker should project more than a smaller speaker and have superior bass capability without that simply meaning cutting all the treble and essentially muffling the tone (which is what I understand by the term 'muddy' tone).
I tried it with 3 different mics and I could pick the difference between them easily.
The tremolo is amazing. To me. I rarely use the trem on my Princeton but in any case it's got nothing on this. I can't explain it, I'm sure. I've never heard any 'effect' quite like this thing. I mean, the principle is well established but maybe it's just the 6SL7 and the particular values in the circuit, the swell and decay of the oscillator was so fascinating when I got it running last night, I just couldnt put the guitar down for a while, I had to keep messing with it.
Or maybe I was just up late and happy to have finally made the trem work.
I was intending to revert the amp to 6v6 tubes but that would involve some more changes which I now consider unnecessary and besides, I'd have to find something to do with the 5881 pair
To sum up, I rate this amp as s worthy harp amp. I'd take it as my first choice to a situation where I thought a champ wouldn't quite cut it and a 410 would be overkill.
I guess it's in a class with my Princeton, and maybe even my 10" 'lone wolf' SE6L6 (though that is a single ended amp). I also have a 1948 filmosound Bell & Howell 2 x 6V6 amp which would be in this class but that's another project. Also a 6SL7 preamp in that one. If I ever succeed in getting that one running (again) I expect it will be King, but that day is still some way off.
For now the Jet is my garage band amp.
I said I'd never sell the Princeton but I really think it's time to revise that idea


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