[Hallicrafters] SX-42 meter

[Ray V.]

Depends on the fuse characteristics. Besides current, voltage and
size/configuration, fuses are also rated as Time Delay, Standard and
Fast. Standard is the typical fuse used in most ham gear although you'll
see the occasional Time Delay (often referred to as "Slo-Blo"). Fast
fuses are specifically for protecting test equipment like meters etc. We
used them in the Navy and I'm sure the other services used the same
nomenclature. Under the military nomenclature you could tell the
characteristics from the ID, for example a commonly used fuse for meter
protection circuits was a F02GR010C or F02GR002C. F02 translates to the
common 3AG or AGC sized commercial fuse of today. The G indicates a 250V
gap voltage and R010 = 1/100th of an amp. The C indicates it is a fast
action fuse. A chart comes with the fuse so you can check the
time/current graph to determine what you need for a particular circuit.
You'd choose which one you needed based on the allowable current flow
thru the meter and how fast you needed it to open. Proper selection
would have the Fast action fuse blow before the meter pegged hard or
burned out. You can get commercial fast acting fuses too but you need to
have the catalog to determine the time characteristics, it's not marked
on the new fuses as part of the info like the military versions.

Ray W2EC

Rick Smedberg wrote:

  > About the fuse to protect the meter the answer is "no". A fuse
  > would never blow fast enough to protect a meter. If it was added
  > it ment there was something else wrong with the sx 42. The best
  > meter protection is two diodes in parallel in opposite directions
  > across the meter terminals. Some of my test meters have fuses
  > but they are really small values. I suspect they were trying to
  > stop the meter from banging against the end on strong signals.
  > Proper meter adjustment would cure that problem.
  > rick
  >