18 watt B resistors

[daz]

Would i be correct to assume they use 2.2k droppers on these amps to get more voltage on the preamp tubes because the 18 watt style PT has a lower voltage wind than PT's for 50-100 watt outputs?

[Malcolm Irving]

Makes sense to me.

It also controls the power tube screen voltage. So we need to look at the screen current (which is a major part of the current through the first dropper) and the desired screen voltage.

EDIT: Disregard this one. I was thinking of the first dropper resistor (usually 2k).

[daz]

The first one is a 2k tho. It's just the preamps that get 2.2k's in the 18 watt. I just noticed that some u8se a 8.2 for the PI tho. Could have swot=rm all preamp nodes used 2.2k. Maybe some clones do and some don't.

[Chuck H]

2.2k works well for me with el84's running hot. You're using 6v6's and fixed bias with more conservative idle current. I might try a 1k between the plates and screens.

If this is the same project from other threads, you have a lot of resistance in the HV rail for the preamp. The schem shows 10k, 10k and then a 15k. You probably have about 150V on the first triode and it takes that stages 22uf filter almost ten seconds to take it's initial charge and recovery is going to be slow too with the first triode sagged to about 130V. You could probably go with less resistance and/or a branched supply to reduce these effects. That WILL raise preamp voltages though, for better or worse. I've never been thrilled with the sound/feel of amps that have 150V or less on the first preamp plate. YMMV.

I'd probably try a 1k and three 5k's and see if the higher voltages don't liven things up.

[daz]

I tried 2.2 for the preamp nodes this morning and didn't like the results. Can't try anything else till i get the new bias circuit working, but when i do i'll replace that 2k with a 1k.