Fixed bias problem "fixed" or when it rains it pours. - DAK - Tube DIY Asylum

Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Fixed bias problem "fixed" or when it rains it pours.

DAK

Hey thanx to everyone who helped me track down the problem. LSS, it came down to replacing the filament transformer which evidently was defective. I tracked it down when i was doing testing during its runaway mode and i noticed that the output from the fil trans was decreasing when it should not be affected.
Unfortunately, at the same time as this i had 2 other unrelated problems that occurred along with the bad fil trans. This really was very frustrating as it meant taking the 50 pound "Big Bertha" back and forth between home and shop.
The biggest headache was using a red LED for the driver tube bias. While this meant much higher gain vs the unbypassed resistor route it also meant that there was much more noise in the circuit. The amplification of spurrious noise may have contributed to the instability of the amp. Not certain about this but i thought it best to take up the LED biasing with a different amp.
So, i went back to the cathode resistor and the output is dead quiet. The other problem indirectly relates to the use of the LEDs. This is because i used some clear plastic tube sockets. Unbeknownst to me is that this type of socket is not heat tolerant. And while playing with leds and resistors and unknown to me one of the tube pins broke off in the socket. This set off another round of troubleshooting as one of the driver tubes would not bias up. Anyway once i changed out the broken solder lug voltages went back to normal.
Anyway, all seems to be ok now and the amp sounds very, very, excellent in every way. Thanks for the help/support/suggestions and best regards, dak

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Topic - Fixed bias problem "fixed" or when it rains it pours. - DAK 16:14:33 01/19/17 (11)

RE: Fixed bias problem "fixed" or when it rains it pours. - sony6060 16:45:02 01/19/17 (10)

RE: I may have had a combo problem - DAK 18:55:04 01/19/17 (2)

RE: I may have had a combo problem - PakProtector 06:41:55 01/20/17 (1)

How do you know who makes them? - DAK 09:20:56 01/20/17 (0)

RE: Fixed bias problem "fixed" or when it rains it pours. - Tre' 17:05:27 01/19/17 (6)

RE:In this case it was a used filament trans.. - DAK 18:46:16 01/19/17 (1)

RE:In this case it was a used filament trans.. - Tre' 20:04:03 01/19/17 (0)

Or hack on new lead outs! (nt) - gusser 17:18:03 01/19/17 (3)

RE: Or hack on new lead outs! (nt) - rage 07:54:43 01/20/17 (0)

RE: What do new leadouts have to do with transformer performance? - DAK 18:41:35 01/19/17 (1)

RE: What do new leadouts have to do with transformer performance? - gusser 10:08:53 01/20/17 (0)

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