[Amps] Dummy Load Blues

[Jerry Kaidor]

Hello,

   To mess with amps, a good dummy load is a must.  I went to my storage,
and pulled out a Cantenna of unknown provenance that I had purchased about
30 years ago at a flea market.  Not knowing what was in it, I assume it's
poisonous PCB transformer oil.  I had kept the dummy load in a plastic bucket
with a hole for the coax, sealed with coax seal.  Now I figured I'd
dispose of the old oil, clean it out, and put in fresh mineral oil.  What
a mess!

   OK, the old oil is gone; it'll be headed to the local hazardous waste
dropoff.  The guts are all washed out in hot water and detergent.  The
heathkit can is toast - rusty and leaking.  The silver
straps around each end of the resistor are broken.  So I can reconstitute
this thing with new silver straps ( luckily I have some silver sheet
laying around ).  And the can - can be replaced with an ordinary one from
the paint factory.  Only trouble with that is - 1 gallon paint cans are
now *plastic*, not metal.  I guess it'll still work, just the heat
transfer won't be quite as good.

   I also scored a 250W load cheap on Ebay.  Seller said it came out of a
cell phone installation.  I popped it open - the resistor is the size
of a postage stamp!  I was messing with one of my SB2-LA's, used that
load - figured a momentary toot from the amp wouldn't hurt it.  I was
wrong.  Apparently these little resistors are not only heat limited,
but *voltage* limited.  I hit transmit, there was a small *pop* and a
puff of smoke.  Hole burned right through it.

   There are similar load resistors on sale on Ebay - 800W for IIRC $40. 
But that's just the resistor, you have to bond it to a heatsink.  I
have
the heatsink from the defunct 250W load - I could machine off a big enough
flat spot for the 800W resistor.... failing that, I have a really big heat
sink in my junk.

                          - Jerry Kaidor, KF6VB