Tube Amp Archive

If you can hold your hand on it without screaming, its ok!

I'd lean towards a 4xEl84, fixed bias power amp with presence and resonance controls. Use a good Marshall style 50W OPT, hammond 290LX power tx, 3H choke... TMB tone stack... heck just build a low voltage JMP with 4xel84 at this point!

too many thingys! im a one or two thingy kinda cat!

whatever happened to "point the thingee to where the sound is most goodest"?

You have exorcised the demons! Full out cathode bias with no NFB and a somewhat gainy preamp tends to be the worst case scenario for fighting hum, nicely done!

Dirty ol' center tap! You might be able to get a further reduction in hum by tying your heater CT to your power tube cathodes for some heater elevation, go easier on the cathode follower section as well. As long as you are fully bypassed it should be a nice clean elevation voltage.

looks like the right hand side bank of caps have individual ground wires (white) running to the ground buss. Maybe connect those grounds locally at the caps with a single connection to the pot ground buss from the lowest voltage supply node? Also consider moving the can cap ground connection to pot ...

nothing jumping out at me but lets get more eyes on this gal! Around the phase inverter, looks like one of the output coupling caps to your PPIMV is sitting below the rest of the terminal strip, is that right against a hummy HT supply node? unlikely to be the source of that much hum but ya never kno...

Can you share some gut shots of the new build? the more detail the better, a few fresh sets of eyes on it might help identify something

Beauty! That is gonna be one quiet power supply... lets the preamp do the talkin'!

https://www.hammfg.com/electronics/transformers/power/229 Check these lil guys out too! If you are alright using a 2nd transformer for your filaments, these dudes still have all the HT current a pile of 12ax7 will ever need. A trim 325dc after full wave rectification and filtering, still plenty of j...

that power transformer is a monster if you are just running a few 12ax7s... id consider going with a smaller one from the 200 series (or 300 series if you need a 220v primary). something like the 369BX (300vct @ 86ma) with a fwb rectifier would get you about 420 volts unloaded... not that the two 12...

nothing wrong with that... just an elevated ground reference via fake center tap for your filaments. Might help with noise!

Another vote for PPIMV here... apart from no global feedback, the PI tail resistor is pretty big for a pair of 6L6, 39k! That likely means the PI doesn't have a huge amount of swing, power tube distortion (if any) will be coming later in the game. In addition to this, the PI power supply node is on ...

could you use a DPDT relay for an extra contact to lift the ground off the mid pot on the stack not in use?