Help me bias my '79 JMP 50 MV

[frtbzz]

I got a Fluke meter and a 1 ohm resistor and alligator clips. I got it out of the box and ready to go. It has 384 VDC on pin 3 so it should be biased about 45ma's give or take a few. Can you tell me where to take the readings to get there please.
Thanks Chris.
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[Lake Placid Blues]

Re: Help me bias my '79 JMP 50 MV

The 1 ohm resistor should be soldered between pin 8 and the chassis ground of one of the tubes. You measure milli volts across (one clip on the ground side and the other on the tube socket side) the 1 ohm R. Adjust the bias pot untill you get 45mv.

Late 70's fifty watt Marshalls had really low plate voltage normally. 395 is what Marshalls old voltage chart for the late 70's suggests, so don't be alarmed by 384 as an intial plate voltage reading. Once biased it it should be around 390ish

 

[frtbzz]

Re: Help me bias my '79 JMP 50 MV

Thanks a lot. My pins 7 and 8 are jumpered and then grounded. So I'll cut the ground and replace it with the 1 ohm resistor and take my readings. V=I*R so Volts are the same as Current in this case as its multiplied by 1:banana:
Chris.