How to use transformer without 50v bias tap?

[T Wilcox]

Hey guys,
I am halfway through a Deluxe reverb scratch build where I am re-using the transformers from a trainwreck express clone I built years ago and never bonded with. Like I said "halfway done" and I just realized the PT does not have a 50v bias tap!
I remember seeing someone mention you could create a bias tap so I looked it up and it led me to Merlins site under the section Bias supplies
http://www.valvewizard.co.uk/bias.html
I copied his example and built a small board for the halfwave bias supply ( his example used Mu of 10 which is exactly what I'm going for with 6V6's) using the exact components
I applied power to the PT unloaded just to check readings and am reading between negative 6 and 12vdc ( through the whole pots sweep) on the wiper of the bias pot
Okay, to be honest I do not know enough about power tube biasing to know if these reading are okay and correct so I guess my next step will be to load the tubes up and check the actual power tube bias and see if it end up in the correct range?
Any tips or suggestions from someone who has done this before would be very much appreciated!

[wpaulvogel]

You should be able to use the exact bias supply as was used in the Trainwreck express. The Express was able to bias the EL34s or 6v6. I think its bias swept from -28 to -35 volts or something like that.

[sluckey]

I would do it like this...

http://sluckeyamps.com/phoenix/phoenix.pdf

[T Wilcox]

You should be able to use the exact bias supply as was used in the Trainwreck express. The express was able to bias the EL34’s or 6v6. I think it’s bias swept from-28 to-35 volts or something like that.

Although I only took out the transformers from the express chassis I did compare the bias circuit to Merlins and it was not much different so I ran with The Merlin one as I has the schem right in front of me.
Thank you for the reply

[T Wilcox]

I would do it like this...

http://sluckeyamps.com/phoenix/phoenix.pdf

This is perfect! Thanks Sluckey!
Its actually very close to what I have now but the values are much different
The first Bias resistor I used a 47K where your drawing shows a 220K
I also used a 10K pot where yours uses a 50KL
I will give this a shot
Thanks again!
Todd

[Snicksound]

I would do it like this...

http://sluckeyamps.com/phoenix/phoenix.pdf

This is perfect! Thanks Sluckey!
Its actually very close to what I have now but the values are much different
The first Bias resistor I used a 47K where your drawing shows a 220K
I also used a 10K pot where yours uses a 50KL
I will give this a shot
Thanks again!
Todd

This is the way it's done on Marshall 50W amps. Works like a charm.

[T Wilcox]

Deleted - false info

[sluckey]

I would do it like this...

http://sluckeyamps.com/phoenix/phoenix.pdf

Hey Steve
I'm working on putting the bias tap circuit together today and looking at your schem I only noticed when going to load the board you have the (2) 10uf bias e-caps +pos connected to ground
Just FYI

I hope you connect your bias e-cap positive leads to ground too.

[T Wilcox]

LOL, I just figured that out
was hoping to re edit the damn post before anyone saw it
obviously nevermind
Enjoy the weekend!