Bias probe

[ronman]

Does any one here use a bias probe to check the bias on a rocket amp. if so what do they usually read on a 2 hole rocket in millivolts.

[rooster]

The ma # *should* be anywhere from 28-40. Actually, just like a Rocket, which some guys here run as high as 45 ma or even higher. This is assuming your plate voltage is 300-315VDC. ...Oh, BTW, the 'mv' number translates to 'ma' with a typical 'bias probe'. Read up on bias probes if you are in the dark here.

Google EL84 bias chart, you should find something with comparable voltage running in Class A to give you an idea.

Is this what you wanted?

[overtone]

For your information: measured across a 1 Ohm resistor at the probe socket I get a range of between 35-50+mA, it depends on the tube I guess.
If the reading moves over 60mA shut it down. That could be a bad tube going into thermal runaway.

Mostly I calculate the plate dissipation and hardly ever use a probe.

[selloutrr]

http://www.webervst.com/tubes1/calcbias.htm


EL84 in Class A (90%) with a plate voltage of 300V = ~ 36.0 mA


use the link above to calculate your bias.