[NLRS] HP 431B question

[Dr. Gerald N. Johnson]

I think I still have a 431B in a box in the basement. I have a 431C 
manual on this computer. First thing to check, there is a switch for 100 
or 200 ohm thermistor heads. The 478A is 200 ohms, not balanced. Then 
you have to manually zero it and the manual says if you can get it 
zeroed on the most sensitive range the error on the higher ranges will 
be under 0.5%. The fact that it shows 0 on NULL means the screwdriver 
zero adjust is set properly. So you have to use the knob to zero it the 
other positions. The 432A meter has more automatic zeroing but one of 
those I have doesn't work right.

You can download the manual from:
hparchive.com/Manuals/HP-431B-Manual-SN233.pdf

73, Jerry, K0CQ

On 5/13/2015 9:09 PM, Charlie Betz wrote:
>
>
> I hope someone on the reflector has experience with this power meter and
> can answer a question.
>
> I was given an HP431B power meter and 478A head for evaluation to see if
> I was interested in buying it. The head is supposed to be good.
>
> I plugged the 478A head into the power meter and powered the meter up. I
> have nothing connected to the N connector on the power head, i.e. the
> input is open. As such, the meter pegs full scale on every position of
> the range switch other than the NULL position. If I unplug the head from
> the cable the meter reads zero on all positions of the range switch.
> What I am wondering is whether or not this is indicitive of a blown
> power head? I suspect it is, but I really have no experience with one of
> these meters, so I really don't know.
>
> Charlie, N0AKC
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