How the crap do I measure IMPEDANCE?!

[bluefoxicy]

Ohmeter. Resistance through a long straight wire, or the same wire in a coil.

Okay but what about IMPEDANCE? RMS of a range of frequencies...

I want to wind a dummy load coil, 16 ohms to parallel across a speaker out to drop a 16 ohm speaker to 8 ohm at a switch, in order to drop a 5K primary to 2.5K to match a 3K EL34 tube. I could use a 16 ohm resistor but it'd be a non-reactive load.

[kg]

Ohmeter. Resistance through a long straight wire, or the same wire in a coil.

Okay but what about IMPEDANCE? RMS of a range of frequencies...

I want to wind a dummy load coil, 16 ohms to parallel across a speaker out to drop a 16 ohm speaker to 8 ohm at a switch, in order to drop a 5K primary to 2.5K to match a 3K EL34 tube. I could use a 16 ohm resistor but it'd be a non-reactive load.

i would not waste my time.

use relatively high value screen stoppers (ie 2k2 or so), strap it up and let it fly.

ken

ps to measure impedance you need an LCR meter or a signal generator + dmm

[bluefoxicy]

i would not waste my time.

use relatively high value screen stoppers (ie 2k2 or so), strap it up and let it fly.


No idea what you just said.

[J Martin]

Impedance bridge

[bluefoxicy]

Got a design for an impedance bridge, thanks!

[Old Tele man]

...some of the "newer" LCR-meters can also measure impedance as well as basic inductance and capacitance, but usually only at 1KHz, I believe.

[kg]

No idea what you just said.

i would not waste my time trying to make a dummy load with the sole purpose of reflecting a "proper" primary z.

i would use high value screen stoppers (ie, series screen grid resistors) of approximately 1-3k ohms in value to protect them from overdissipation and tube failure, and i would run the amp.

you have to consider why you are trying to make a "perfect" primary z by adding dummy loads on the secondary?

if it is to reduce wear on the tubes, you also have to realize you will be wasting a substantial amount of output power in the dummy load. that is power that must be generated by the power supply and modulated by the output stage, which (unless your amp is fully class a) means it will be dissipating more power and getting more wear and tear.

there are some amps out there (can't remember the brand off the top of my head) that use a good quality OPT and label the impedance switch as a "tone control." i subscribe to this idea.