Altec 1567A buzz.....ideas?

[sparechessroom]

I used the original power transformer just for the plate voltage for the n2 12ax7 tubes in the Altec mixer that I used and I left the OG xformer where it was.

I made a chassis for the buffers and their xformers, which I put behind the mixer and secured in a rack shelf which I put the whole thing in.

I made a new power supply which feeds all the heaters and just the buffer/mix plates. This was shielded in a little chassis, and the toroidal xformer was mounted on the very rear.

the xformers will def induce a lot of hum if close enough to the mic stage, but after killing myself with all the things I see people talking about in the thread, I really did discover that the original output tube stage is incredibly noisy, and though it has a lot of gain, again, the new mix stage I used has more gain and is infinitely quieter.

the dc heater supply helped a lot.

incidentally I also used a dc standoff for the heaters in that design, which also knocked a ton of hum out.

 

[sparechessroom]

sorry, I am mixing something up... the Original supply has a DC heater supply. I used it for just the heaters in the unit, which were just the preamp tubes, 2 x 12ax7's. then I used the brand new supply for all the plates in the Altec, and the new buffers. I doubled the filter capacitance in the original heater supply and rewired it.

 

[emrr]

The output stage in all four of these were not noisy.