[ARC5] ARC-5 dummy load

[Dennis Monticelli]

The old thermcouples in those RF ammeters are often inaccurate.  Aging
takes it toll. You can easily check them by passing either DC or AC and
measuring the current with a bench current meter.  Usually they read low.

Dennis AE6C

On Sat, Aug 20, 2016 at 4:38 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net>
wrote:

> Found a bag 100 ohm 5 watt wire wound resistors the other day. I didn't
> what to do with them, so I tried making a lo-z dummy load for the
> ARC-5 /SCR274 equipment.
> 10 of these in parallel is 10 ohms, 50 watts. You say "hey those are
> inductive WW resistors!" . Yes but the inductance is greatly reduced in
> parallel.  In fact at 3.5 mhz it was 5+j17 which is more than swamped by
> the series 100 pf transmit cap (-j454).
>
> The TX units are supposed  load into 5 to 12 ohms with high capacitance,
> so it's in the sweet spot.
> The resistors got warmer than I thought they would, although the meter
> said it was pushing 2 amps. That's only 40 watts.
> There is some serious reactive voltage at the cap. I had the cap barrel
> laying too close to metal and I saw some blue corona discharge.
>
> I'm a bit suspicious of this BC442 meter which never seems to budge above
> 2 amps. I get the same max current with a 5 ohm load!!
> Are they known to be inaccurate?
>
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