Author Topic: Cathode bias method SUNN 200S  (Read 3118 times)

0 Members and 1 Guest are viewing this topic.

Offline doc10039

  • Full Member
  • ***
  • Posts: 32
Cathode bias method SUNN 200S
« on: October 06, 2010, 06:21:55 pm »
Is it possible to install a 1ohm 2watt metal oxide resistor between pin 1 and pin 8 and then to chassis ground. I see there is a 18K resistor from pin 1 and 8 to the first point on the bias pot can this be removed and replaced with the 1 ohm resistor to ground from pin 8 is this the case with SUNN amps also? On Fender amps you can only ground with the 1ohm resistor from pin 8 to ground. The bias circuit looks similar to the hum balance on the Silver Face Fenders. I also have a lot of hum and noise when it is being used any help will be appreciated.


Thanks
« Last Edit: October 06, 2010, 06:46:01 pm by doc10039 »

Offline loudthud

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1,167
Re: Cathode bias method SUNN 200S
« Reply #1 on: October 07, 2010, 10:54:30 am »
Move any wires that go to pin 8 including the 18K resistor to pin 1 and install the 1 ohm resistor between pin 1 and pin 8. Hum can be from mismatched tubes or a bad filter cap. If the current doesn't match between tubes within 10% or so, swap the tubes between sockets to verify that the problem is the tube, not a problem with the socket. If the problem is with the tubes, try a different pair.

Offline doc10039

  • Full Member
  • ***
  • Posts: 32
Re: Cathode bias method SUNN 200S
« Reply #2 on: October 07, 2010, 07:57:35 pm »
There is also purple and black wires running from pin 1 and 8 back to the terminal strip. Remove these also back to the strip?