[R-390] Speaking of TO-6As...

[Bob Camp]

Hi

I'm sure the marketing departments at each of the companies that made 
them had long lists of exactly why theirs was the best on the market. 
 From what I have seen they basically are all balanced bridge 
instruments. If you replace the "standard" capacitor in one of the arms 
the main issue is to hit the value correctly.

A reasonable way to do a quick check on any of these gizmos is to have 
a metal package tubular teflon dielectric precision capacitor sitting 
around. Value is not real critical as long as it's in roughly the same 
range as the R390 capacitors. Teflon caps have a very high insulation 
resistance. Metal can parts generally last a long time. You should be 
able to trust the markings on the part, even 20 years later. If the 
meter reads the indicated value and a very high insulation resistance 
(say > 50 gigaohms) the meter probably is working just fine for R390 
purposes. There's nothing in an R390 that needs anything close to that 
kind of insulation resistance.

	Take Care

		Bob Camp
		KB8TQ


On Apr 3, 2005, at 8:53 AM, Mahlon Haunschild wrote:

> Hello, list.
>
> Was given a Sprague Tel-Ohmike TO-6A yesterday.  Free was a good price 
> in this case, since all of the paper capacitors in the unit need to be 
> replaced, and also because the meter is blown and needs to be 
> replaced.  Not unlike what I went through with my Heathkit capacitor 
> tester a while back (the two "standard" paper capacitors in it were so 
> leaky the bridge never balanced; same thing is going on with the 
> TO-6A).
>
> Has anyone ever run across a calibration procedure for these?
>
> regards,
>
> Mahlon - K4OQ
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