need info on mystery shallcross component

From Web search Shallcross became RCL Shallcross and was then taken over by IRC which was then acquired by TT Electronics plc.

The 2MEGOHMS value definitely marks it as a resistor, the length would tend to indicate high voltage and the diameter, high power. The clip in fuse type mounting suggested is even more of a mystery. I can't see anything in the current TT range which fits those possibilities.

Hey don,,,most components will have these ratings on them to specifically tell you exactly what they can handle. Usually the higher the amperage the bigger the physical size. There are instances today where we are using high voltage in smaller packages though. Always remember this and you will never forget a simple way of how they rate these things. Voltage is written as pressure, I also look at it like voltage can jump. the higher the voltage, the higher it can jump. If you ever pulled a fuse from something that runs on regular 110 v house current you may notice that the fuse is rated at blah blah amps and 250 volts. The 250 is a rating indicating that there is no way that the fuse is unsafe below those voltages. You shouldn't get voltage jumping out of the glass tube or across. Above that, a whole nother world, touching both ends of an open (burnt fuse) circuit, while its plugged in and you become part of that circuit and can get hurt bad. The amperage can usually be found written on there somewhere. Some of those fuses though actually say 1.50 or 15.0 or 150. amps and the dimple may be hard to see so get a mag glass and look again. Be carfull handeling capacitors, just like a battery, they can store juice, enough to kill you. When in doubt dont touch. If you want to send me a pic to show what this stuff looks like I can most likely identify all of it.

The Tooth.

Don - Remember, just like 22Mohm resistors in 1/4W and 1/2W packages, just because the package is conventionally called "1/2 Watt" that you cannot dissipate 1/2W in that resistor because you will hit the dielectric limit of the package first.

Tim.

Um, I think it works the other way.

Five kilovolts would be over twelve watts. Higher voltages would exceed the power limit.

Which I do not know what is.

Educated guess-- a 150W 2M carbon tubular resistor, non-inductive. Works out to 17kV and change in this case, which is plausible from the creepage distance. Probably has a thoroughly nasty tempco.

I've used smaller similar parts made by Carborendum. I think I still have some smaller (but different) Shallcross parts kicking around somewhere because they were unusual enough to be worth not tossing.

As always, worth what someone else is willing pay for it.

Best regards, Spehro Pefhany

Does it ohm at 2M? Where was the surplus house... anywhere close to Los Alamos?

Maybe it's a 2 meg resistor good for 300 million volts.

John

Um, the power dissipation might be a tad high at that voltage. By something between a slew and a passle.

The device does measure just under 2 megs. I forgot to compensate the radio shack multimeter, so the capacitance is around 12 pf, not the higher figure I misstated.

The 150A pretty much has to be a poor choice of part number.

Possibly somewhat small for 150 watts of dissipation. But 15 kv and 112 watts looks possible. I suspect the holder has to do some heatsinking.

Surplus house was in downtown Phoenix (Electronics Emporium div of the Equipment Exchange).

I suspect most semiconductor surplus houses are now in deep s*it because of ROHS.

In light of

You might want to look at the Wikipedia page. (Don's been doing this longer that you have been alive.)

Once, when I was in the USAF, someone ordered a 15A fuse, but messed up one digit on the stock number. We got a 15A, 15,000V fuse. It was shaped just like a 3AG, but about a foot long and about 3" in diameter. The barrel was glass, and it was filled with sand.

We took it apart to see what was inside, and there was a ceramic post with a cross section very much like an asterisk: '*', with five little wires spiraling down its length.

When we got the ends off, and all of the guts out, nobody knew what to do with the components - I think somebody made an ashtray with one of the ends, and somebody took that 3" diameter, 3/8" wall glass tube and made a bong.

Cheers! Rich

I suppose returning it to the supplier for credit would have been too much trouble...

Best regards, Spehro Pefhany

Yeah, "too much trouble" pretty much nails it - this was in the military, so they just write it off and buy new stuff. Every year we had to throw away thousands of dollars worth of spare parts, because we were supposed to order stuff from stock, so they wouldn't lose their budget allocation.

Our tax dollars at work, right? :-/

Thanks! Rich