Quick PSE biasing question

[ECV02]

Hi all,
Just double checking, while plotting PSE loadlines, each tube sees double the OPT's impedance, right? For example, while plotting load lines with a 4k5 pri, I should use 9k as my figure in PSE?

Thanks,

E

[shooter]

Goes the other way same as when you put 2 same value resistors in ||, they become 1/2 what they used to be 

[ECV02]

Wait, so each tube sees half the OPT pri?

[DummyLoad]

Wait, so each tube sees half the OPT pri?

a tube burns 10 watts and it has a load: two of the same like type tubes in parallel burn 20W and they share the same load - has the load resistance doubled or halved?

--pete

[ECV02]

I've been following the rule of thumb that a safe load impedance is (Vp^2)/(Pdmax). I'm using 12BY7's in PSE, so I've been treating them as one tube with a 13w max plate (6.5w each). 250v plate. (250)(250)=62500, 62500/13 is roughly 4.8k. Doing this with one tube yields exactly double that value.


Is this not correct?

[DummyLoad]

yes. since your initial calculations were based on two tubes, load for one tube will be double the value for that of two tubes. IOW, 4.5K load for two tubes, 9K for one.



--pete

[shooter]

I've been following the rule of thumb that a safe load impedance

I gave up on "load line analysis" because I get distracted easy 
I now use tube datasheet "values" for Class A(1) single tube.  for load I simply take the D.S. value for 1 n divide by # of tubes used, (I I've done 1-4SE)
I give each tube it's own Rk and set current per datasheet, then I tweak each Rk to "balance" current.
I also use an OT rated "1 amp size up" so a 10W SE gets a 15W OT sorta thing, once you hit 25W you get to the "cliff" of SE, tons of $$'s gets you very little return on investment

[ECV02]

Alright, so just recapping, I should use 9k for my load lines. My OT is 8w, so I think that'll be ok. I shouldn't get more than 6w out of this setup anyways. The 12BY7 datasheet doesn't provide a load resistance value, inconveniently 

Thanks for the help,

-E

[PRR]

One 12BY7: 250V 30mA would like a 7k-10k load. So two 12BY7 would like a 3k-5k load.

Note that two 12BY7 have the same dissipation and power output as one 6V6, but eat 2.6 times the heater power (at unconventional voltage) and double the pins to wire. They will slam with about 1/7th the grid swing, but mere gain is a ton cheaper than power; add a gain triode.