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previous: Mike T Hi Stephen,Good to hear fro... -- 12/26/1997 9:35 AM

Re: Cathode Bias Idling Current

12/26/1997 7:59 PM
Stephen	Re: Cathode Bias Idling Current Yes...you have a small typo there, but I assume you mean (35/250)/2 = 70 mA I usually do the mental arithmetic as (35 x 1000) ----------- =140mA TOTAL 250 but it comes out the same either way More resistance = less current Less resistance = more current . But it's not quite a linear relationship, so if you tweak the resistor value, measure volts again and recalculate total current for the new resistance value to check it is ok. BTW, I hardly ever use the current range on my DVM. I put 1 ohm resistors in all output tube cathode leads, Then 1mV across 1 Ohm = 1mA through it...35mV indicates 35mA. Doesn't upset bias or tube curves significantly, and you can at any time check the individual tube currents without disturbing the circuit conditions. Things in NZ are ..."middling-fair" I'm doing more housekeeping and cooking...but hey, it's mid-summer and there are fresh raspberries in the garden for Christmas dinner. Could be worse Cheers, Stephen

12/26/1997 7:59 PM

Stephen

Re: Cathode Bias Idling Current

Yes...you have a small typo there, but I assume you mean (35/250)/2 = 70 mA
I usually do the mental arithmetic as
(35 x 1000)
----------- =140mA TOTAL
250
but it comes out the same either way :-)

More resistance = less current
Less resistance = more current
.
But it's not quite a linear relationship, so
if you tweak the resistor value, measure volts again and recalculate total current for the new resistance value to check it is ok.

BTW, I hardly ever use the current range on my DVM. I put 1 ohm resistors in all output tube cathode leads, Then 1mV across 1 Ohm = 1mA through it...35mV indicates 35mA. Doesn't upset bias or tube curves significantly, and you can at any time check the individual tube currents without disturbing the circuit conditions.

Things in NZ are ..."middling-fair" I'm doing more housekeeping and cooking...but hey, it's mid-summer and there are fresh raspberries in the garden for Christmas dinner. Could be worse :-)

Cheers, Stephen

Replies:

Mike T I just fired it up and something is... -- 12/27/1997 9:21 AM