The Amp Garage

Don't forget power outlets with a RCD.
Cheers
Ian

The 370FX Hammond was fine in the amp I built for Neale. I do agree that a smidge more current capability may help. He is a vintage rock and blues and folk guy and never pushes the amp. Continuous Sine Wave testing (400Hz) gave 28 Watts on the edge of clipping. That is right out of what the data boo...

Not made up my mind on 4 x EL84 vs 2 x 6L6 etc. But the last big project I did for a friend was a London Power Standard with the power amp changed to run 4 x 6V6 into a JTM45 Output Tranny. That had heaps of low end authority, but then 6V6 is a 6L6 Baby brother. Ran the 6V6 with B+ of 340V (at 100% ...

It is a paraphase splitter. That means it will work best with the cathodes fully bypassed. This is approximated in the original circuit as the 2 equal'ish triode signal currents are out of phase and so no net AC signal at the cathode. From voltages on the schematic I calced the cathode DC voltage at...

In your photo - are the caps on the left the main B+ supply. 3 off 10uF/150V caps? If so then they need replacing with 450V rated caps. the bottom one looks a bit like it has a bulged end. If this is the case it would certainly account for your motorboating problem. If they are something else then i...

PSUD2 does give the ripple current, it appears in the capacitor RMS current column. Ignore the 1st second where inrush currents are large and look at the value for the next second or so and choose caps to suit that ripple current. Be conservative. Due to the current squared x ESR heating power inter...

I think you have too many stages connected to the B+3 +300V power supply node. Split off a separate power supply node (that is, a separate decoupling resistor and cap for the reverb recovery circuitry). I think when you start to swing signal in the reverb circuit you may get positive feedback to the...

The parallel 12AU7 triodes of the cathodyne are running at just under 2mA total. you could easily use 12AX7 parallel triodes instead. I believe that the 12AU7 was used to try to lead the behaviour when you overdrive the output tubes, may also have less voltage across the tube so leave more signal sw...

Had one here for ages. Burn Channel had been modified and the instruction was to put it back to original. I did that and then gave it a test run. At 8 or 9 or above on Gain 1 or gain 2 it would whistle at me. Actually a bad design with 3 gains stages of the burn chan all off the one power supply nod...

Looks good so far. Nice to see bias test points on the rear panel.
Cheers
Ian

RJ, I re-read that thread, particular the stuff I posted to it. Would stick by what I said there. With Ultra Linear you have larger Miller capacitance at the output tube grid which probably will not make any difference for a Bass Amp but might for a HIFI Amp. Would also recommend MOSFET source follo...

Then it wasn't a Class Y safety rated cap and was illegal. Must have been before Class X (Active to Neutral) and Class Y (active or neutral to ground) was ïnvented". Lucky the only death was the cap itself. Safety Tip for old amps - if you are not going to get rid of the death cap entirely then seri...

Also note that a 12AX7 has a zero current voltage rating of 550V. So no need to worry about startup with cold heaters and zero current.
Cheers,
Ian

Search this forum using the search term Junkbox to find my Junkbox Trainwreck schematics.
I run a parallel triode input BUT with the two triodes at different operating points for some harmonic emphasis.

The use of 2 triodes paralled give you a root 2 improvement in signal to noise.

Cheers,
Ian

Does your amp have a FVM (Fender Vox Marshall) Tone stack?

Poor mans mid boost by switching in a second cap across the cap feeding the top of the treble control.
The existing cap is usually 270 pf up to 470pF, try a 2n2 switched across it for a mid boost.

Cheers,
Ian