Thunderchief Q2 bias problem

Started by Mihkel, May 22, 2006, 01:31:01 PM

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Mihkel

Alright, I have wired up the Thunderchief with the original tonestack as shown here: http://www.runoffgroove.com/tc-tone.png and have set the drain voltage to 4,5V on all fets except Q2. Turning the trimpot only makes a 0,1V difference, as does a 100k fixed resistor.

Any ideas would be greatly appreciated.
Thanks

Mihkel

I should add that I accidentally connected the power supply with the wrong polarity at first, but fixed that. Could it be that just one FET bit the dust because of this?

RDV

Did you socket the FETs? If not, I would. I had trouble with Q3(which would be Q4 on the schem you're working with) myself which I solved with a fix from FAQ on the ROG website.

RDV

Mihkel

Changed the FET, same problem.
Should I try using a smaller resistor instead of the 1k?

syndromet

I had the same problem with my Fetzer-valves. I found that connecting the 9+ to lug 1 on the trimpot, lug two to the jFET and lug 3 to ground made me bias it correctly. I guess this would work here too.
My diy-site: www.syndromet.com

Mihkel

I go to check that resistor out and what do i discover?
I have no 1k resistor in there!
*smacks head*
I installed a 2k2 resistor, the closest value to 1k that i had on hand, and it biased correctly.
Still, theres no sound coming out of this thing.
Touching the gates of the fets after Q2 makes a buzzing sound.
It's probably the fet though, I don't really have any new ones left, just old ones that might be dead.