Question about BIAS Marshall JTM 60

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Yes the OT winding resistance will change as the amp warms up, perhaps more so than might be expected from copper's temperature coefficient of 0.393%/C.
So it's best to measure the OT resistance after the amp has warmed up for a bit, eg 15 mins; obviously it will need de-energising before the measurement is made.

[torcamaniac]

So, did a run-over of all the mods and checked most resistors and caps.
Connected a PC-Fan to heater supply.
2016-12-26 14.01.19.jpg
Aslo making a place near the top handle to put the vent in.
2016-12-26 14.01.48.jpg
Increased the capacity of negative bias caps. I added to each of the two 10uF (C139 and C140) two new 10uF elkos parallel, so now I have 20uF and it lowered the hum when you bias hotter. I'll be adding a 5H choke in place of R113 anyway...
Changed some coupling caps in preamp. Funny the schematic says that C118 is 4,7nF and C119 10nF. In my amp they were 1nF and 2,2nF...
Also changed C125, C126, C128 and C129 in PI stage just to be sure...
Changed the feedback resistor R201 to 330kOhm. The schematic says its 100kOhm but mine had 150kOhm. Not sure if there is a difference after doing this anyway...
Anyway now I'm biased (used OT resistance/voltage method) at 35mA so around 65%, the bias negative voltage is now at -39V. Seems fine...