V4 preamp tube subs for Channel 1 and 2?

[beedoola]

I just got a V4 again that was modded for 6550s. I haven't opened it up to ensure everything is as it should be - I see the added bias resistor but haven't checked to see if the screen resistors were changed. 

I'm trying to experiment with settings with my A/B switcher to get a semi clean tone on one channel and then some good crunch on the other. One thing is I like the mids a bit more pushed to really unleash the beast but then the "clean" channel isn't as clean say with a more scooped mids: 300hz switch with mids at 9 o'clock.

I was wondering if I could drop in a lower gain preamp tube for channel one to give it more headroom. Thoughts/suggestions?

[Hangman]

Beedoola,

Definitely check the screen resistors, they need to be 1k 5W. The 6550s sound great in the V4, but consider moving on to a KT-88 when these crap out. I have found that the KT-88s take the high screen voltage better.

I've heard of people swapping the preamp tubes, I don't think it will get you very much, as the power amp will distort well before the preamp in the V4.

When you say you want more headroom, what exactly are you looking for?

-Hangman

[beedoola]

I have a quad of JJ 6L6s I could try. Will I need to change the screens back to 470ohm if I want to try the 6l6's after trying the 1k/6550s?

Also, I need to add a bias trimmer. I had seen someone previously post (in an old thread of mine) a 47k resistor in series with a 50k trimmer. Would that work to bias both the 6550s and 6l6s?

In terms of headroom, I was hoping I could get a little more clean volume before breakup on one of the channels, which was why I was thinking of the preamp swap but I get your point about power amp distortion before the preamp will.