borrowing a bias supply

[mbailey]

ok I'm working on my 5e5a I don't have a bias tap on the power trans. so I decided to borrow one from the secondary but I'm having a little trouble figuring out the circuit. here is where I'm at so far coming off of pin 6 of the rect. tube into a 6.8k res. then a in4007 and a 100uf cap(reversed) for filtering. I have installed a 10k pot to make it adjustable, i have not wired this in yet as i'm having trouble at this point. anybody wanna point me in the right direction as this is really all I lack to being finished with the wiring.
thanx
MB

[tubeswell]

ok I'm working on my 5e5a I don't have a bias tap on the power trans. so I decided to borrow one from the secondary but I'm having a little trouble figuring out the circuit. here is where I'm at so far coming off of pin 6 of the rect. tube into a 6.8k res. then a in4007 and a 100uf cap(reversed) for filtering. I have installed a 10k pot to make it adjustable, i have not wired this in yet as i'm having trouble at this point. anybody wanna point me in the right direction as this is really all I lack to being finished with the wiring.
thanx
MB

You need to make a voltage divider. So as well as the resistor in series with the bias supply, you need a resistor to ground, in parallel with the reverse-biased cap. The voltage divider is a proportional mechanism as much as an absolute mechanism, and the voltage you get can be obtained from combinations of two resistors as long as the proportion of the limiter (series) resistor to the bleeder (ground) resistor is consistent.

Work out the resistors for the voltage you need here:

http://www.tpub.com/neets/book1/chapter3/1-35.htm

or here:

http://sound.westhost.com/vda.htm

For the bleeder/ground resistor you can wire in a trimpot wired as a variable resistor, in series with another resistor, to make the voltage supply adjustable.

[scole]

why not do it this way
http://www.el34world.com/charts/Biascircuits.htm

[clyde1]

If there's no bias tap, try a (all values approximate) 120K/2w in series with a 33k/1w from one leg of the pt to ground. At the junction of these 2 resistors, or similar values of same, hook up your diode, cap and resistors or pot just like in any amp with a bias tap. Hope this helps.

[txstrat]

I've done it in the way of a 6G11 Vibrolux and it works great. You might have a look here:
http://www.schematicheaven.com/fende...6g11_schem.pdf
I mean just to use a tap of the sec. HV with a 100k resistor. The rest like every other amp.

[mbailey]

This is exactly what I was looking for! I have looked all over the internet but apparently did not phrase my search correctly. I sincerely appreciate the help.