The Amp Garage

Do you have a schematic?

Back to the original discussion: yes, the scheme of using variable resistors for most Rs would make sense when prototyping (or just use a breadboard).

Totally understand, and I have a modified 1987 circuit with 6L6s running 220K (LARMAR PPIMV). That waveform you posted looks like cutoff distortion, IMHO. Thus, you're getting cutoff in the power amp -or- just before and getting it amplified. Usually generated from tubes operating well outside desig...

Just to be persistent, did you ensure that the grid loads on 6L6 were reduced to 100K total from pin5 to the bias supply? That's the total of load and stopper resistors. I'd ensure that your power amp values are within published tolerances, and working correctly before modifying to match a particula...

Haha - I read this post title and thought it'd be a discussion of room acoustics

Basic fundementals of electronics is a must. I recommend taking a first semester basic electronics course (i.e. electronics 101) at your local community college; audit it but buy the books. Invaluable.

Also, I just noticed prior post where you mentioned 6L6 power tubes. Make sure you're not vastly exceeding the grid load (resistance to ground/bias) for fixed bias operation of ~100K per the 6L6GC tube data sheet.

Have you double-checked bias on the power tubes?

I know you're getting lots of suggestions. Did you perchance try a lower value for the 1M paired grid loads in the PI yet? Simple would be to just temporary tack in another pair (say 560K) to bring down the value and determine if that alters PI breakup tone.

You may have already stated this, if so I apologize. Did you try replacing the PI tube? Try both brand and type (12AX7 vs 12AU7). In my experience, with PPIMV amps the tube and tube type can obviously change overdriven tone also. I've also never had luck using a 12AT7 in PI slot on PPIMV circuits, a...

I'm not up to par with the actual theory at present (use it or lose it), but I ran into similar symptoms with a build once ~10 years ago. These two things helped my situation: 1. Lower the value of paired "grid load" resistors in the PI (typically 1Meg). I used 330K. 2. Change the type (not value) o...

Very trebly and not very active controls, I would suspect the "slope resistor" connections in the tone stack. Saw this once on a Budda Superdrive 80, just a bad solder joint but same exact symptoms.

HeeBGB wrote:I've had a few. Had a Chevelle SS, Z28 and so forth. But I ended up with these. I ended up selling them both.
[img:75:75]https://farm8.staticflickr.com/7700/17194118922_d81425fc68_s.jpg[/img]

Both 1973? I had 1972, 1978 silver anniversary, and 2002 Z06. Used to go to Carlisle a bunch.

I have the Mag Components JTM50 PT in my gigging amp (1987 clone with 6L6GC and extra preamp tube). It gets warm but has been fine going on 4 years now. Unless you're running a constant sine wave through it, I think you'd be fine with the appropriately spec'd Stancor.

Bogner support was great when I had a Shiva years ago. It sounds an awful lot like a cell phone signal, with that steady pulse; but since it's not happening on the other channels maybe not? Could it be that clean channel doesn't have the same amount of heavy shielding and snubbers that the dirty cha...