Tube Amp Archive

Love the way the JJ's sound when you push them.

40 ma @ 470 volts will be about 18.8 watts at idle (disregarding the screen current). You are well within the operating specs of the tube. You could even run it a bit hotter, I would think. Looks like as long as you avoid extreme settings, and go by ear you won't damage anything. BTW, I like the "ea...

I've seen scope shots that clearly indicate cutoff in an AC30 at higher output levels. It would seem to be the case with the the DR. Z, I would think. I often operate my own EL84's up to 14w. Some can take it, others not so well. I have no reservations about using modern tubes as perishable items if...

Red-plating means the tube is biased too hot. If you drive the grids too hard you will hear some really ugly sounds (blocking distortion) long before seeing a red glow on the plates. Check the bias after changing anything in the output section to make sure it's still in line. As for the steep loads ...

Plate dissipation at idle is not the same as output watts, however at close to class A operation it will be nearly the same. Going from 30w to 45w is going to be less than 3db increase in output. The important thing is to not exceed the max idle dissipation for an EL84 (12w).

Yes, but the 2-tone later model was not the same circuit. Alas, the wonderful 6SJ7's were gone. I'm sure the later one was wonderful in its own kind of way, but certainly more ordinary 12AX7's into 6V6's. Yeah, mine is the later version. I'll rebuild the cab with 3/4" pine and tu-tone tolex, althou...

Hey Loctal, is that Stumptown, WV?

Since the Traynor has a silicon rectifier I would not be too concerned with doubling the value of the first supply cap (C18). This will certainly help with the bass response and should reduce the hum some. 40 MFD for the other three is probably OK. What concerns me is the 450 volt ratings. The schem...

Thats interesting. Can you post a pic?

Mountain Switches has round ones that are strong. They have illuminated ones in red and green in many configurations including on-off-on and on-on-on. The round hole mount (15/16", I think) is too easy and they look cool. Get 'em from Mouser.

I spent a whole day tracking down a bad hum problem before noticing the fine print on the guitar cable I was using..."speaker use only". I now store them separately from my guitar cables.

Switch the B+ as it leaves less of the amp energised to high voltage and ready to hurt someone being careless with it. Not sure I see what you mean. Seems there would be fewer points energized with no CT ground. Certainly no charging of the filter caps. The only potential would be between the secon...

Yeah, I can see that. Wouldn't be practical for most B+ derived bias supplies. I'm thinking more about inrush current or effect on tube versus solid rectifier circuits. Or anything else that might be affected.

Some amps switch the HV on and off at the PT center tap (to ground) vs. in the B+ line. I'd be interested in anyone's opinion on this. It seemed to be more common on older amps, however it's still used today. Pro's? Cons?

Hey guys, I haven't really thought your problem out, but I had a SF Twin that was burning up tubes one-at-a-time and it turned out to be an open ground wire on the board (I can't remember which one). Is the board warped? I haven't seen many older fender fiberboards that stayed flat over the years. Y...