Gibson Thor Bias?

calebbarton · #1 07-23-2010, 10:49 AM

Does anyone know how the bias is adjusted in this amp?

sneha1965 · #2 07-23-2010, 10:56 AM

johnk_10 may chime in on this or you might PM him. I know he has one as listed on his sight.

http://johnkvintageguitars.homestead.com/Thor.html

KramerBassFan · #3 07-23-2010, 11:31 AM

Tube, right?

I want to think its Cathode biased....

stiles72 · #4 08-02-2010, 01:03 PM

The photo is of my amp. As far as I know it's Cathode biased, like an old Portaflex, so there is no trim pot to adjust the bias. I'm not a tech, and I haven't had to replace tubes yet, so I'd ask Johnk_10 to see if he can verify.

BassmanPaul · #5 08-02-2010, 04:06 PM

If the amp is cathode biased there is no need or way to set the bias. Cathode bias is also known as Self bias. Even if it is fixed bias an amp of the age would probably have no means of varying the level.

Paul

Passinwind · #6 08-02-2010, 06:10 PM

It is a fixed bias amp, with the bias supply derived directly off the HT transformer. You most certainly can adjust it, just change the voltage divider resistors. You, meaning a properly trained tech, of course...

http://www.freeinfosociety.com/elect...onthorbass.pdf

calebbarton · #7 08-12-2010, 10:50 AM

ok, thanks guys!

BassmanPaul · #8 08-12-2010, 11:06 AM

Quote:

Originally Posted by Passinwind

It is a fixed bias amp, with the bias supply derived directly off the HT transformer. You most certainly can adjust it, just change the voltage divider resistors. You, meaning a properly trained tech, of course...

http://www.freeinfosociety.com/elect...onthorbass.pdf

Yes it CAN be changed but the bias circuit will need to be modified. As stock it's a one trick pony.

Paul