Never seen a resistor like this...

Thermionics

Post Whore In Training
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Discovered this in the process of deconstructing a donor amp. I've never seen a resistor like this before, but it appears to be rated for 3 ohms. I'm assuming it was used for measuring bias on the tube (although no idea why they didn't use 1 ohm). Is this a wirewound? There doesn't appear to be any insulation on the body (unless the wires are enameled).
 

Thermionics

Post Whore In Training
It is indeed a wirewound. My best guess is the the ceramic covering cracked and fell off, leaving it's giblets nude.
The odd thing is there were no ceramic bits floating about in the chassis. Given the age of this particular amp, I'm wondering if someone sold a version with exposed wires like that in the 1950s when you were allowed to buy chemistry sets with uranium in them. ;)
 
Since there's no gap inthe windings, the wires would have to be enameled.
Looks more like an inductor rather than a resistor. McIntosh uses something similar on they're tube amps.
What amp is it?
 

Thermionics

Post Whore In Training
Since there's no gap inthe windings, the wires would have to be enameled.
Looks more like an inductor rather than a resistor. McIntosh uses something similar on they're tube amps.
What amp is it?
It is a mystery amplifier. Was built with an outboard PSU (not included). Four octals (two signal, two power) with 0.2uF coupling caps between the driver / inverter stage and power tubes. 0.5uF between the two stages of the driver / inverter circuit. If I were so inclined to trace out the entire circuit, I'll bet I'd find it was a Williamson, especially given the Acrosound TO-300 output transformer (which is why I snagged it). Whoever built it was really good at what he did - layout is impeccable and the parts are really nice (e.g. tube sockets are Cinch, coupling caps are C-D 'greenies', the one power cap is a Sprague Atom dry electrolytic, the power resistors are Ohmite Brown Devils while the signal resistors are all Allen-Bradley carbon comps). There's even honest-to-god wire lacing.

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I feel almost bad stealing the OPT from it, but it is destined for better things.
 
Wow, you're right, that is a clean build! Almost like something my grandfather would have assembled. (His Heathkit projects were impeccable; I'm only upset that I didn't think to grab the tube integrated amp and tuner before my uncles tossed that all at the curb.)
 
If the use is similar to what McIntosh does they go on the plates of the output tubes.
Mac refers to it as a plate choke. It keeps the amp from oscillating.
 

Thermionics

Post Whore In Training
So where in the circuit is it used.
Mr Coronadope has been around tube stuff a while. Smart guy.

If the use is similar to what McIntosh does they go on the plates of the output tubes.
Mac refers to it as a plate choke. It keeps the amp from oscillating.

And you would be right. It's between the plate and the OPT.
 
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