[ARC5] Testing BC-442 Thermocouples

[Leslie Smith]

  Hi Mark & Group,
  I believe I've seen an article dealing with the reconstruction/repair
  of RF thermocouples.
  I believe I got the article from Brian, VK2GCE, but lost it in a disk
  crash.    
  (It's not totally lost - just on a disk on a PC I can't boot at the
  moment).
  Brian is a reader on this list, and he'll be able to confirm my memory
  (or memory failure).

  This is probably "old news" but the thermocouple generates a few mV
  due to heating in the thermocouple junction.
  Thermocouples typically fail when oxidation between the two
  dis-similar wires creates a "hi-Z" junction, defeating the
  thermocouple action.

  If Brian is "silent" (or away) I'll look (dig, dig,dig) for the
  article this weekend.

  73 de Les Smith
  vk2bcu at operamail.com


On Wed, Aug 14, 2013, at 12:40, Mark K3MSB wrote:
> I have a pair of BC-442 Relay Units on the bench and I’m trying to
> determine if the internal thermocouples are working.
> 
> For general testing of RF Ammeters I use my Variac at 20V through a 20
> ohm
> series resistor.
> 
> I tried that for both Relay Units and I get no meter deflection.  I’m
> tapping directly into the “B” side of the pickup transformer.
> 
> I’m suspecting the pickup transformer won’t work at 60 Hz.   I tested the
> meter directly and it works.
> 
> Thoughts?   Other ideas how I can test the unit (aside from just putting
> in
> the actual circuit, which I will after I clean up some cruddy relay
> bypass
> “mods” in them….)
> 
> 73 Mark K3MSB
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