Best NEW 7591[A]s

[Shrapnel]

Ok thx on the AX7 currents

Hmm... now 5u4 (1.2) @ 375 = 450 (274BX) OR gz34(1.3) @ 350 = 455 (273BX). 175ma Should do the trick for them, with a little room to spare.
(Whoa is me with these if I get 10mA on all triodes though. -> 250-300mA would be needed then for max output on the 7591A, depending on preamp config)

Thinking of a SLO type front end with perhaps 1 or two more channels (for 2-4 channels ttl) 30-45w out, prob aim for 36w though.

[zaphod_phil]

Sounds like it might be more of a project for PPwatt.com then....

[Shrapnel]

Only if I don't go for the 36watt point, or squeeze it down to the 18watt point. I should probably investigate the details before commenting further then. After all, these should be decent for 36watts.

[now to go do the math and get the data figured out and then post it ]

[Shrapnel]

Someone check my math plz.

I believe the 7591A will hit 36w at the following:

Vp=400v
Vg2=350v
Vg1=-17v OR Rk=260R
Zpp= 6k6

IF I am in err, plz show me how you came up with your answer so I can compare.

I'll calculate for 18w later (Vp~300v).

[edit] found data for a 37w output... Vg1 was -16v Vp, Vg2, & Zpp was same.

[klingo]

i think the datasheet ask for a 6K6 Zpp load in fixed bias (Vg1=-17v) and a 9K Zpp load in self bias (Rk=260R)
i haven't done the math but you can adjust the fixed bias or swap the cathode resistor to keep your 7591 happy.
as Zaphod said, with the same amplification factor than EL84, the 7591 seems to be perfect for a bigger 18W.

[Alexo]

Yeah, I wouldn't worry about hitting exactly 36 watts, suffice to say anything between 30 and 40 watts will be in the right ballpark. Just watch your screen current if you're going by hi-fi specs that don't expect you to slam the amp into distortion.

[klingo]

+1 on what Alexo said.
looking at the datasheet, i realised these tubes are screen current greedy.
2x1K not bypassed screen dropping resistors after the 350v supply seem to be the minimum.

[morcey2]

We disassembled a Conn organ yesterday and it had 2 7868s in it. The tubes were all pulled before I found out about it, but they're all in storage and I'm trying to get my hands on them. They're 7591's in a magnoval (novar) bottle. I've got the sockets and OT, so what was originally going to be a 7591 18watt will now probably be a 7868 18watt.

It's gonna be fun!

Matt

[Shrapnel]

Sounds like it, I can't wait to finalize my pre as well as the little details on the 7591s... (Not necessarily the JJ 7591S) and start getting everything together. Money's tight in this economy so it might take me a little to raise the funds.

I know what ya mean on those grids. 3.3w, but up to 6w when it's working it's magic Guess I better source 10w grid resistors.