PT centre tap floating via resistor?

[Guitarist]

Hi, I've been working on a Japanese Kent amp that is sounding killer now. I see it has a 470Ω 10W resistor going to power supply ground from yellow/red wire emerging from the secondary. I don't see any center tap on the PT and suspect its here. Should I just pull this baby and get more headroom?

[R.G.]

It's impossible to say without
(1) knowing the more-complete schematic of the amp
(2) knowing the voltages across the winding sections of the transformer
(3) knowing that more headroom is desirable - it may not be.

You say it's killer sounding now. If it's not broke, why would you fix it?

[Guitarist]

Alright R.G., I leave it as it. It's destined for recording so it loud enough for even a bit of feedback and that's fine. It's a Kent BA 170 and mostly rebuilt now, but done.

[g1]

It may have been added to drop B+ due to modern AC voltage increases. Someone may have thought that the B+ was putting tubes or capacitors in danger.
As RG said, if it sounds great, leave it. Removing it without doing a lot of investigation may alter the sound as well as possibly blowing up components.

[Bruce / Mission Amps]

It might be to develop some kind of low bias voltage... especially if everything else (common mode) is referenced to that PT side of the resistor... have you drawn out a schematic?

[Dave H]

Yeah, you definitely don’t want to replace the 470R with a short circuit if it’s for back biasing. The 6th post down on here Kent BA-170 says -

“I don't get it, there's a 10k and some cap in series connecting the leads to the OT. Apparently nothing on the cathode and 470ks off the grids that just go to another 470 to ground instead of some kind of negetive bias supply.”

The ‘10k and some cap’ look like a conjunctive filter and the ‘470 to ground’ looks like back biasing to me.

[Guitarist]

Too funny, hey Dave H. I had just added the 'conjunctive filter' comment for him and had to join that forum first. He was mistaken as the 6v6 cathodes did have a wire going to the caps' can 30uF and it's 250Ω resistor- cathode bias.
the whole secondary wiring looks standard with the 5v heating the tube rectifier, the HT AC leads, heaters; it's just that one wire. Well it's all good and delivers tones nicely. These are good amps with some weird approaches that benefit from reworking. It started out very bland however. BTW I changed the PI to include a 6u8 pentode and fed that into cathodyne. The preamp is one other 12a*7 tube.

The only thing is it might benefit from running V1 on DC. I injected the bias into an added floating 100Ω heaters node, pretty standard. I might tag on the boogie DC approach and reference heater ground via new 33Ω resistors; which I trust I can do or should I first remove the added 100Ω resistors and return the heater winding to unreferenced/floating?
Thanks.

[kingswayguitar]

wow. very nice sound indeed

[Dave H]

Too funny, hey Dave H...

Ha Ha! you beat me to it. I did wonder if Doug H was the same Doug H on here but then didn't even notice that the last post was from Guitarist, Doh!

[Guitarist]

I since recapped the PS, added a loop and a Line Out with a 30Ω attenuator off the OT secondary. I even put it direct into the Line in of an Audient iD22 interface. So one can record it with multiple circuit "taps" at once— into Logic...