Hello Everyone!

[danfrank]

I’m a new member here on LatheTrolls. I have many years experience with audio electronics, especially vacuum tube based audio electronics.
My main reason for joining is that I’ve built a pair of power amps based on the Gotham PFB-150 cutter amps and I’m looking for info on correct bias current for each 811A output tube. In past builds I have run them at 66ma each tube and am wondering if biasing at higher current (75ma each?) or lower current is what was originally intended…
I have not found the answer on the sparse info on these amps that is online but I’m willing to bet that someone here has or has had this amp or has worked on them.
Thank you for your time.
Daniel

[markrob]

Hi Daniel,

Just in case you don't have this document. See the attached pdf. It seems to have quite a bit of info. Looks to me that they spec 75ma as the bias point if I am reading correctly. See page 7.

GothamPFB-150WA.2.pdf

Mark

[danfrank]

Thank you so much Mark! That’s exactly what I was looking for. The amp sounds great at 66ma per tube but higher current should give more power output in A2, which is what I’m mainly interested in.
Thanks again!