Adjustable cathiodbiae

[menger66]

Is.It possible to.Adjustable cathode bias, it's for a pair 6v6
I'd like to be able to adjust between 400and 480 ohms [/quote]

[xtian]

Hi, Mark...are you trying to type with your toes? Nice job!

Using a switch would be easy. But maybe you are asking about using a pot or rheostat to adjust the cathode resistor value?

[jjman]

I use 2 470ohm resistors + 2 100ohm pots on a pair of 6v6s to do this. Pots are 5wt wire wound. Each has its own bypass cap.

[Stevem]

Since you are going thru the added effort to set things up this way you may as well give yourself 100% control and install a seperate resistor and bypass cap for each tube plus a 100 ohm 2 watt wire wound pot in each so you can balance or unbalance to suite your distortion nature like's.

Also in each add a 1 or 2 watt 1 ohm 1% resistor so that by placing a ohm meter set for DC across it you can directly measure the tubes current.

[tubeswell]

You could find a '470R' wire-wound resistor that measures 480R and put a 2k2 to 2k7 resistor in parallel with it on a switch

[RJ Guitars]

I used a big rheostat on one of my Rockster builds. IIRC correctly it was something like a 100 ohm 50 watt rheostat that I put in series with a big chassis mount resistor. This allowed me to test out a variety of output tubes and I eventually settled on KT-66's as my favorite tubes for the Rockster. You can find big rheostats pretty reasonable priced on eBay.