Multimeter question

[PRR]

> I usually put a 10 ohm resistor in series with the output tube cathode

Your age is showing.

Yes, I have used 10r because old needle-meters' low range was 1.5V. 50mA in 10r is a half-Volt which can be read with good precision.

10r is "usually" insignificant to a tube. The biggest audio bottles have cathode impedance of 50 Ohms or more, another 10r is little or nothing to them. When you *beat* a 6550 to a 400mA peak, 10r makes another 4V drop on what is probably a 35V swing, small difference.

Note that dissipation of 10r in a BIG amp can be 0.8 Watts. Most amps will never roast a 1/2W but I have smoked 10r 1/2W in big amps.

DMMs change that. They are 199mV in their heart, and can be trusted to a few mV (or better when you get above several dozen bucks). 1 Ohm reads directly in mA (no need for an abacus or computer to do a divide-by-10. (Our future?)

And 1r is insignificant to any vacuum tube we will ever have. Also the worst-case dissipation is under 1/10W, so small parts are ample and a commonly sold 1W part will never drift.

[deadastronaut]

i got one of those component testers...(with the case for about 7 quid) .amazing little things, very handy .