6V6 18Watt Parallel V1 Tuning Help

[ncusack]

Hey Everyone,

My last rendition of this 18watt I'm working on had a cascaded preamp and that just had too much gain for me to work with. Since giving up on that build I've changed things around and paralleled V1 instead of cascading stages. Now I have 260Vdc B+ feeding the parallel triode and that puts 135VDC on the plate with a shared 100k plate and 820R cathode bypassed with 1uF.

What I'm finding with this build now is that there isn't enough hair in the amp anymore. Now I checked the bias and it was only dissipating about 9W per tube and at that setting I only got a distorted sound with everything dimed. Now I have it biased to about 13W per tube so this may have fixed what I was experiencing but I haven't tested things yet.

What I'm wondering is if the re-bias doesn't get me where I want would a simple increase of the v1 plate likely do the trick?

My current build schematic with voltages is attached.

[sluckey]

What I'm wondering is if the re-bias doesn't get me where I want would a simple increase of the v1 plate likely do the trick?

That may work. I'd try 220K. Using a 50µF bypass cap may help too, but it will also increase bass response.

Not an easy solution, but, using EL84s would definitely add more hair.

[jojokeo]

What I'm wondering is if the re-bias doesn't get me where I want would a simple increase of the v1 plate likely do the trick?

That may work. I'd try 220K. Using a 50µF bypass cap may help too, but it will also increase bass response.

Not an easy solution, but, using EL84s would definitely add more hair.

Exactly as EL84's are driven much easier than 6V6s. I can't see the schem at the moment but anytime you parallel a 12ax7 and share plate & cathode resistors they are effectively cut in half value-wise. So sharing a 100k plate & 820 ohm cathode resistors means each triode stage effectively has 50k plate & 410 ohm resistors. Not good and not helping this amp if true?

[sluckey]

So sharing a 100k plate & 820 ohm cathode resistors means each triode stage effectively has 50k plate & 410 ohm resistors. Not good and not helping this amp if true?

That's the way the normal channel on the original is wired and it has plenty of hair. I really think the main problem is just under driving the 6V6s. Going back to cascade preamp and managing the gain is probably gonna be the best bet if you want to stay with 6V6s.

[jojokeo]

That's the way the normal channel on the original is wired and it has plenty of hair. I really think the main problem is just under driving the 6V6s. Going back to cascade preamp and managing the gain is probably gonna be the best bet if you want to stay with 6V6s.

If it were me I'd dump those values if ran parallel that way.
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