bias circuit not adjusting HT Club 40
Posted: Fri Jan 31, 2020 10:19 am
Hi guys, new member here...and apologies if this has been covered somewhere. I did search but found nothing...
Trying to bias up a pair of tubes in a Blackstar HT Club 40. I work on tube amps a lot, so the general procedures and principles are well known to me, however, in this case I am getting -72 volts on the screens (pin 5) - effectively switching off the tubes - and adjusting the bias pot has no effect on this. (Measuring 0mV at the test point, too) I suspect a fault in the bias circuit, or in some part connected to the PIC chip, which seems to turn on the bias circuit?? Anyone out there with knowledge at this level?
Cheers,
Defy
Trying to bias up a pair of tubes in a Blackstar HT Club 40. I work on tube amps a lot, so the general procedures and principles are well known to me, however, in this case I am getting -72 volts on the screens (pin 5) - effectively switching off the tubes - and adjusting the bias pot has no effect on this. (Measuring 0mV at the test point, too) I suspect a fault in the bias circuit, or in some part connected to the PIC chip, which seems to turn on the bias circuit?? Anyone out there with knowledge at this level?
Cheers,
Defy