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View Full Version : Bias range for JMP style amp

iggs
10-12-2006, 11:09 AM
What is (in general) bias range in mA for a 50W EL34 JMP style amp?

Thanks!
Swarty
10-12-2006, 01:05 PM
I'd say 30-45mA depending on taste and wildly fluctuating plate voltages (360-490V). They vary greatly and there is no hard fast timeline although early amps, circa '68/69 tend to be of the high voltage varieties while later '70s tend to be the lowest, but you can find high voltage examples later and low voltage examples earlier.
iggs
10-12-2006, 03:05 PM
Thanks for the info, I figured it would be *somewhere* in that range ... it's not a Marshall and it's not vintage but the amp is modelled after the 1987 Ali.
sundaypunch
10-17-2006, 12:17 PM
Your best bet is to get a Bias Rite so you can check plate voltage easily. Here is a good resource for bias ranges for various tubes / plate voltages.

http://members.shaw.ca/house-of-jim/Html/bias_tables.html
iggs
10-17-2006, 12:22 PM
Your best bet is to get a Bias Rite so you can check plate voltage easily. Here is a good resource for bias ranges for various tubes / plate voltages.

http://members.shaw.ca/house-of-jim/Html/bias_tables.html

Yup ... BiasRite already on order! :AOK