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previous: ChrisM You do need to use an ammeter in se... -- 4/13/2000 8:52 PM

Re: Marshall 1987X biasing question

4/13/2000 9:06 PM
Matt	Re: Marshall 1987X biasing question What was alluded to was the transformer shunt method, which I personally do not recommend for beginners. For the original poster, do not pass go until you've read the tube amp faq at www.geofex.com. Reading current using the TS method doesn't require breaking into the circuit because the current is being shunted from the transformer through the mA meter. This is accomplished by the principle of path of least resistance... The transformer has around 150+ ohms DC resistance, where the mA meter will have maybe 2 or 3. Ohm's law will say that most current will go through the low resistance of the meter when shunting the transformer. With a good quality meter, the current read via this method is acceptable as a plate current reading. I'd recommend the 1 Ohm cathode resistor bias method for beginners. Matt

4/13/2000 9:06 PM

Matt

Re: Marshall 1987X biasing question

What was alluded to was the transformer shunt method, which I personally do not recommend for beginners. For the original poster, do not pass go until you've read the tube amp faq at www.geofex.com.

Reading current using the TS method doesn't require breaking into the circuit because the current is being shunted from the transformer through the mA meter. This is accomplished by the principle of path of least resistance... The transformer has around 150+ ohms DC resistance, where the mA meter will have maybe 2 or 3. Ohm's law will say that *most* current will go through the low resistance of the meter when shunting the transformer. With a good quality meter, the current read via this method is acceptable as a plate current reading.

I'd recommend the 1 Ohm cathode resistor bias method for beginners.

Matt

Replies:

Rebel420 q{I'd recommend the 1 Ohm cathode r... -- 4/13/2000 9:12 PM
peter Thanks for that, I didn't understan... -- 4/13/2000 9:15 PM