A Sensitive Instrument Research Corp. model JW. This was something I bought at auction 35 years ago for the sole purpose of setting up the bias current on my then modified ST70. This is an edgewise panel mount meter, but is fully encased in a heavy cast metal housing finished in black wrinkle varnish. The scale is white with a gold mirror strip to minimize parallax when reading the 0-100 ma scale. The scale is marked in 2 ma increments. Zero adjust screw is on top and connection is made via a pair of terminal posts in the rear. It features a diamond pivot movement. And, it's got it's own serial number. This thing must weigh about 6-7 lbs. I always thought it would look great mounted in a walnut panel or in a piece of audio furniture of the period. Only date on this thing is 1960. For $100, I will carefully pack it and ship it (CONUS only, please) to your door.
I think that your price is a little bit on the high side on this one. I've seen them go for $25 on ebay. Its nothing special. I would suggest putting it on ebay.
Since most amplifiers generally have a small value resistor from cathode to ground it is customary to use a VOM and measure the voltage across the resistor and set the bias that way.
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