DIY dummy load?

[Dingleberry]

Hi.

I found one of these big variable wire wound resistors from a flea market for 1€. Does any of you have slightest idea what could be the power rating of these big boys and would it be suitable for use as a dummy load while scoping an amp? I see no reason why it wouldn't.
The ohmage ranges from zero to about 24ohms.
There is a metal tag on the side stamped: 3AMP and 21ohm.
No mention about voltages.
Does that power rating vary with the ohmage, I mean that if you slide it to 8 ohms there is twice as much wire handling the injected power comparing to 4 ohms.

Or should I just borrow my friends major and see if it glows red hot it's made for 100W use only...

There are couple pics, what do you think?

-T

[Zippy]

"3 Amp" likely indicates the current handling capacity of the wire - don't exceed that current.

[Dingleberry]

That's what I kind of thought too.

-T

[David Root]

If it's limited to 3 amps and the resistance goes to 21 ohms, then theoretically 3x3x21=189W. It appears to be in good shape, but I wouldn't crank a Major on it.

OTOH no amps I know of have 21 ohm OT secondaries, so............. using 16, 8 or 4 ohm loads, 3x3x16 ohms = 144W, 3x3x8ohms =72W and 3x3x4 ohms = 36 W. So unless I'm missing something those are your power handling limits at each OT impedance, without exceeding the 3A wire limit. This assumes 3A RMS.

[Reeltarded]

I wouldn't use those for anything, because I am a scared little girl when it comes to guinea pigging more than one thing at a time.

Give one to a dumb 'friend' who has more luck than sense, I say!

Can he test my tube? Ask him.

[Dingleberry]

If it's limited to 3 amps and the resistance goes to 21 ohms, then theoretically 3x3x21=189W. It appears to be in good shape, but I wouldn't crank a Major on it.

OTOH no amps I know of have 21 ohm OT secondaries, so............. using 16, 8 or 4 ohm loads, 3x3x16 ohms = 144W, 3x3x8ohms =72W and 3x3x4 ohms = 36 W. So unless I'm missing something those are your power handling limits at each OT impedance, without exceeding the 3A wire limit. This assumes 3A RMS.

Did the ohm's law calculations too last night and got the same results.
Simple formulas, but so valuable tools.
Should have realized myself too that if you know two out of three, you can calculate the third... After all this ain't quantum physics we are talking about but tube amps. Thank's for confirming my conclusions.

-T

[Structo]

Wow that's a monster resistor!

You could probably heat your house with that thing!

[billyz]

Wow, that is a neat one. You scored dude. I 'll buy it from you.