Tube Amp Archive

Yes, explicitly. The PT CT should go to the negative of the first filter cap FIRST, and NOT to the star ground. It should NOT go to the star ground first. This is because the rectifiers charge the first filter cap with large pulses of current. These high pulse currents into the (+) side of the firs...

Do you mean without first connecting to the ground connection, which would be: PT/CT -> minus(res.cap) -> starGround instead of: PT/CT -> starGround <- minus(res.cap) :?: Yes, explicitly. The PT CT should go to the negative of the first filter cap FIRST, and NOT to the star ground. It should NOT go...

Would there be problems if I let it like that, meaning one side ofvthe filament wirining at 1.5V and the other at 4.8V? It appears to be quiet then... It helps to understand what is happening when the filament voltage is offset. AC filaments are center tapped because the AC voltage across them indu...

Would there be problems if I let it like that, meaning one side ofvthe filament wirining at 1.5V and the other at 4.8V? It appears to be quiet then...

What could be the reason of the hum pot acting like a hum volume pot with minimal hum on 1 side and maximum hum on the other side?
The hum is also barely audible with the volumes on zero

It looks like 1 heater wire gas all the hum and the other has none?

Stevem wrote: ↑Sat Jul 23, 2022 11:10 pm What happens if you remove the heater bias up voltage altogether?

Louder hum

Ok I made some progress with the hum. Turned out to be a short in the shielded wire from the wiper of the heater hum pot. I attached the shield on 1 side to the back of the pot and clipped the other side + shrinked it off. On the 50V DC elevation I kept reading 0 V. Now I cut the shielding from the ...

In terms of buzz type of noise, have you tried laying out a big sheet of foil on a counter top and sitting the amp open side down on it? The volume controls in each channel are after the first two gain stages so that nails it down to something common to both preamps. You stated you have one hum on ...

Something like that - but the "Power Cord Green Wire" bolted appart... ChassisGrounds2.png ... maybe? EDIT (as I look at it more carefully:) isolated speaker/output jacks, really... :?: aren't the pot touching the chassis already before you add the ground buss?! The buss at my pots doesn't touch th...

That's how i did this one. I always do it this way.
Maybe it's those 6SL7 tubes that hum. The hum pot is doing its job well enough though.. there's another hum on top of that..and that's the one I'm trying to eliminate

I run a ground bus for all preamp stages and one for the power stage. And the dedicated mains ground of course. Dead quiet, never fails. Try jumpering the pot ground to the preamp ground. If not successful connect the board ground also. That should be conclusive. I'm not exactly sure what you mean.

So... after biasing the cathode for the 64 mode and the fixed one for the 66 mode I cant get rid of a hum. It's definately grounding related. It is dead quiet with both volumes at zero and gradually increases with the volumes turned up. I used the grounding system with all preamp going to the ground...

Naah... maybe it's best that I keep that optional then. If it doesn't work out I can always do the 1 tube reverb and use the extra tube for a cathode follower on the lead channel.
Thanks

Hi I was wondering if there is likely to be trouble when I would dedicate an additional gain stage in an unused triode of the reverb recovery tube. The gain stage is for normal preamp gain structure as in: V1a 1st stage, V1b cascade stage 2, V4a tonestack driver, V4b reverb recovery V2a and b are cl...

In that philosophy shouldn't it be better to switch the unused channel to ground after each 1st stage? Then there is very little signal going through each unused channel? This may or may not be better. It depends. If your layout and wiring is such that there is stray coupling between the two channe...