Taming my 60s Ampeg J-12

[Boze]

I have an all original sixties Jet I'd like to play through more. Trouble is I find the usable volume range to be from the bottom to the top of the 1 on the volume knob and even then I need the tone under 3.5.

Granted I'm only playing at home and don't need/want to crank it, but since it only has two working knobs (I didn't pay the experienced tech who replaced the power cable and cleaned it up to try to fix the tremolo) I'd be happier if I could use both of them a bit more.

Is there an option to swap a preamp or power tube or something so it's not such a hothead? Pics below show the tubes it takes. Maybe it would be smart to shop the bay for NOS backups at some point.

[Jimmy Mack]

This doesn't sound like a Tube fix, sorry.

[powerwagonjohn]

An inefficient speaker can quiet it down a bit. Depends what's in there now. I have a 62 Ampeg Reverberocket that is in living room rotation now. Also turn the guitar down. learn to live with the amp, it's worth it!
Thanks John

[garybaldy]

My Marshall JCM 800 4014 is like that. I just turn the guitar's volume right down. The sound is amazingly vintage albeit slightly distorted!

[Boze]

I should have shared some pics with my initial post even if there's nothing that will let me get to 2 on the volume without developing tinnitus.

I love the amp, just wondered if there was a way to get less out of it, as it were.

I should probably go back to the repair guy and have him try to fix the tremolo at least.

[nevershouldhavesoldit]

I had 2 small Ampegs back in the early '60s (J12, then Reverberocket), and neither one behaved that way. I wonder if someone replaced the original log taper pot with a linear taper and/or incorrect value volume pot. Something isn't right if it reaches maximum volume by 10 or 11 o'clock. That's typical of some Fenders, e.g. the Blues Deluxe. The cure (apart from changing the pot, which is a good way to deal with it) is to substitute lower gain preamp tubes (12AY/U/T) for the 12AX7s.

Check to be sure someone hasn't substituted another tube for the 6SL7s that should be in yours. There are a few pin-identical alternatives - 6AQ6, 6AT6, 6AV6. Some have substituted 5751s, too. Some of these need resistor changes to tame them - check to be sure you don't have subsitutes there.

[Cavalier]

Hammertone should pitch in. I used a 60s jet quite o bit and that isn't stock. I'm thinking it has the wrong resister on the input.

[rpjazzguitar]

My 64 Reverberocket with the same tubes (except rectifier) has a gradual taper to the volume. The tone control also affects volume.

My first thought was like Never's. Wrong taper on the pot?

[Boze]

I had 2 small Ampegs back in the early '60s (J12, then Reverberocket), and neither one behaved that way. I wonder if someone replaced the original log taper pot with a linear taper and/or incorrect value volume pot. Something isn't right if it reaches maximum volume by 10 or 11 o'clock. That's typical of some Fenders, e.g. the Blues Deluxe. The cure (apart from changing the pot, which is a good way to deal with it) is to substitute lower gain preamp tubes (12AY/U/T) for the 12AX7s.

Check to be sure someone hasn't substituted another tube for the 6SL7s that should be in yours. There are a few pin-identical alternatives - 6AQ6, 6AT6, 6AV6. Some have substituted 5751s, too. Some of these need resistor changes to tame them - check to be sure you don't have subsitutes there.

The lower gain preamp tube was what I was wondering about, although none of the tubes in this J-12A are 12Aanything.

Are the pair of 6SL7 the power tubes? The label has two tube names (6V6) scratched out with 7591 written in and then 5Y3 for the last one. I wonder if the tech needed to replace these and didn't say anything specifically about it or if that pen is old too like the A by J-12? Hmm

[nevershouldhavesoldit]

The lower gain preamp tube was what I was wondering about, although none of the tubes in this J-12A are 12Aanything.

Are the pair of 6SL7 the power tubes? The label has two tube names (6V6) scratched out with 7591 written in and then 5Y3 for the last one. I wonder if the tech needed to replace these and didn't say anything specifically about it or if that pen is old too like the A by J-12? Hmm

The 6SL7s are the preamp tubes. The 6V6 / 7591 issue may be part of the problem. The two tubes are not directly interchangeable. There were 2 versions of Ampeg models with those tubes as I recall, with a switch from 6V6 to 7591 sometime around 1963. But the circuits are not identical and you can't just substitute a 7591 for a 6V6. If you aren't familiar with electronics, you might want to take it to a tech who can tell you which circuit it is and whether it's been set up for the tube complement that you got with it. If someone tried to convert it to the later circuit (which was brighter and louder than the 6V6 version) and didn't do it right, your problem may require some component juggling to sort out.

[Boze]

The 6SL7s are the preamp tubes. The 6V6 / 7591 issue may be part of the problem. The two tubes are not directly interchangeable. There were 2 versions of Ampeg models with those tubes as I recall, with a switch from 6V6 to 7591 sometime around 1963. But the circuits are not identical and you can't just substitute a 7591 for a 6V6. If you aren't familiar with electronics, you might want to take it to a tech who can tell you which circuit it is and whether it's been set up for the tube complement that you got with it. If someone tried to convert it to the later circuit (which was brighter and louder than the 6V6 version) and didn't do it right, your problem may require some component juggling to sort out.

Thanks very much; this sounds like a promising lead to chase down. I got the amp from the original owner, a retired gentleman who got it as his first amp as a kid, and he had it in storage for decades. I'll take it back to the technician and draw their attention to that crossed out power tube.

This is something I'd have done well to revisit when I picked it up. It's just that I'd never heard the Jet working before and didn't know if the too loud too soon thing was normal.

Thanks again. This shop takes several weeks to repair things but I'll post again if/when I get a resolution.

Oh, and would it be safe/smart to try 6L6 power tubes on my own to see if it's any better? What's the 5Y3 one do?

[nevershouldhavesoldit]

[QUOTE=Boze;1374030]Oh, and would it be safe/smart to try 6L6 power tubes on my own to see if it's any better?[/ QUOTE]
No!

The 5Y3 is the rectifier.

[Boze]

[QUOTE=nevershouldhavesoldit;1374033]

Oh, and would it be safe/smart to try 6L6 power tubes on my own to see if it's any better?[/ QUOTE]
No!

The 5Y3 is the rectifier.

I'm sorry, I meant 6V6 like the og label on the amp indicates

[nevershouldhavesoldit]

I'm sorry, I meant 6V6 like the og label on the amp indicates

I wouldn’t do anything without knowing what the circuitry is.

[Cunamara]

I have a tweed Deluxe amp and what you're describing is similar to how the volume knob works on it. From 0 to 3 is loud. I leave it at about 2 and run the volume knob on the guitar at about 4. Gives me a very nice tone, keeping the amp clean and suitable for the living room. Playing with a band, the volume knob on the guitar goes up to 5-6, depending on the output of the pickups, but the amp stays the same unless playing outdoors or something.

I noticed that on the label, the model name was changed from J-12 to J-12A with a pen, as well as scratching out the 6V6 tubes and substituting the 7591. I wonder if that wasn't actually done at the factory, using up old labels for a change in specification in the circuit. I agree that knowing more about the circuit before making any tube changes would be wise. It might be that there is a resistor on the input that has drifted out of spec or that when the amp was gone through the wrong value was put in.

[rpjazzguitar]

I vaguely recall learning at some point that the factory did make changes to that label in pen.


In case it’s not obvious it also may be worth looking for the schematic on the inside of the back panel. That’s where it is on my 1964 reverberocket.

[nevershouldhavesoldit]

In case it’s not obvious it also may be worth looking for the schematic

Given the nature of the problem, the age of the amp, and the undocumented state of the circuitry, doing anything without first determining exactly what’s inside and to what schematic it conforms is risky.