Adding adj bias to 5e5a update

[etneccas]

I did not pull the board to remove the underside jumper to the grids so that the jumper could be located after the 25kl pot
As a result I still have -45vdc on pin 5 of the power tubes
I basically removed the 56 k resistor after the diode and install the 25kl pot ( variable resistor) in series with a 33k resistor and now have a bias range of 26ma to 50ma
Does the -45 on pin 5 still have to be lower?

[sluckey]

I did not pull the board to remove the underside jumper to the grids so that the jumper could be located after the 25kl pot
As a result I still have -45vdc on pin 5 of the power tubes
I basically removed the 56 k resistor after the diode and install the 25kl pot ( variable resistor) in series with a 33k resistor and now have a bias range of 26ma to 50ma
Does the -45 on pin 5 still have to be lower?

If you simply replaced the 56K with the pot and tail resistor and did not remove any underboard jumpers, then your circuit will look like the attached pic. The fact that your bias changes between 26mA to 50mA means that the -45v on pin 5 of the power tubes also changes. Check it and you'll see that with the bias set to 26mA there will be some value of negative voltage on pin 5 of the tubes. Then as you adjust the bias pot to increase the bias current toward 50mA you will see that the negative voltage on pin 5 decreases.

[etneccas]

That is exactly how everything is wired now
I’ll take the pin 5 Voltage reading again as suggested
I have TAD 6L6WGC’s Installed and have 420volts on them
and biased at 36ma
How can I get more clean headroom out of this amp?
Even with a lower bias it still breaks up quite early
I built it off of Mojotones schem/WD and used there stock kit parts for everything
I feel this is the perfect amp for me,if only I could get it to break up a little later

[pompeiisneaks]

Looking at the schematic of that thing, you could adjust the cathode resistors of the input stage or even others.  It starts with an 820 ohm that's putting it on the hot side, I'd guess upping that to 1k or 1.5k would help.  Dumble seems to even go up as far as 3k on some to bias them even more cool.  (Or at least, that's my understanding of the thing)  I have a friend that has an epiphone electar 10 that's got a 'drive on it that's pretty anemic, mainly due to the first tube being biased at 3.3k which made it nice and clean, more headroom.  This meant adding the second stage of gain didn't push it very much.  I adjusted the 3.3k down to 1.5k and he got a lot meaner sounding drive on that thing a lot quicker. 

~Phil

[etneccas]

Mojotone has a 12ax7 in V2....,
I think I’ll try a 12ay7 there.....

[sluckey]

I don't usually think of tweed amps as a clean sounding amp.

[ac427v]

I think you are on the right track with a 12AY7 in V1. My tweed Bassman clone has some similarity to the tweed Pro. And it sounded like mush with a 12AX7 in V1. But with any 12AY7 it is almost clean at moderate volume and has that great tweed string definition. I say any 12AY7 because I have used NOS RCA and new production EHs and they all sound great. I have also changed the V1 cathode resistor from 250uf to 25uf to 2.2uf to reduce excessive bass response and bass distortion. The tiny 2.2uf was the final winner there.
--Craig