ampeg J-12D low volume

[themusic]

Recently acquired a ampeg J-12D . Seems to have only about 1/2 volume. I install a filter cap kit from fliptop.
Swapped all tubes , new 7591s, one good 6k11 and a new 6c10... I have check all voltages on schematic and they all seem within
range. I've gone thru every resistor and cap " I pulled all caps for testing and replaced were needed. I believe I'm down to the output
transformer. Is there a simple way to test... there quite expensive to replace thanks

[Justin Thomas]

Hey themusic,

First, I have a J12-D with a similar problem. Second, that amp calls for 6<B>K11s, not 6K11s. I think the 6K11 has one or two lower-gain sections. I've also heard that the 6C10 will not work in these amps without some kind of mod, although I have never been able to find out what those might be... As far as I can tell, the only differences are something about an internal shield on one of the pins versus nothing, or some other pretty insignificant thing like that. And I think I got the last two 6C10s on Earth a few years ago, for $35/pop.

Good luck on your quest, sorry I couldn't help much. A signal tracer may be in order; so you can find where the signal is going to, stage by stage. I made one, then realized I need to make a new "more precise" one due to the chassis design. As far as the output tranny, honestly, I'd use any kind of available generic replacement. These are guitar amps, not NASA lab equipment, to paraphrase Enzo.

Justin

[themusic]

yes my bad I have the 6bk11 installed . the 6c10 will work as a replacement I've used them before. I've put the good 6Bk11 in V2. The V1 is just for the tremolo.
Thanks ... I still believe it's down to the output transformer... I also replaced speaker just in case

[Justin Thomas]

So a bigger question is, where in the Hades did you get a 6BK11?

Justin

[Leo_Gnardo]

I thought this model Jet took a pair of 6BK11, all high gain triple triodes. There are some subs you can get away with, but not all triple triodes will do. If there's an overall lack of gain have a look there.

Is there a simple way to test... there quite expensive to replace thanks

Not really. You can measure how much power your OT is sending to a resistive load, if it's way low then your OT is suspect. The other method is substitution, for that you don't have to have the exact replacement OT. If your power figure picks up significantly, say goes up from a watt and a quarter to 11 watts, you know what the answer is: gotta replace it.

I haven't checked Fliptops' price for the appropriate OT, but I can tell you, over the years I've replaced dozens of bad Ampeg OT's with ones intended for Fender Deluxe Reverb, very affordable and nobody has complained. FWIW I've just been thru this within the last month, and now have a terrific sounding Jet some lucky guitarist will buy and love.

[Justin Thomas]

I thought this model Jet took a pair of 6BK11, all high gain triple triodes. There are some subs you can get away with, but not all triple triodes will do. If there's an overall lack of gain have a look there.

Leo, they call for 2x6BK11, but the ONLY possible sub for a 6BK11 that MIGHT be available (although about $100/each) are 6C10. Both Compactron, both three sections of u=100. But otherwise, there's not really a lot of options. Mine had a 6K11 & a 6AV11 when I bought it, and it also had low gain and a non-op trem. 2x6C10s later, the trem works but the volume is still low. I gotta signal trace it.

Justin

[themusic]

I have a fender deluxe trans I'll try this evening...thanks... I was lucky to have a good 6BK11 that was in the tremolo side. Also I bought the 6c10 new.
Didn't matter were i put them same results...thanks