On Fri,1/8/2016 3:49 AM, d.e.warnick@comcast.net wrote:
I've got one in Dover that I haven't used in years.
It's not uncommon for one or more of the HV filter caps to be dried out.
Nothing destructive happens, you'll simply get reports of hum. Fix is
easy -- power it down, let the HV discharge, open up the PSU, find an
analog VOM, and measure each cap in the string on a medium high Ohms
scale. For each cap, measure in one direction, then reverse the leads,
notice the strength of the charging current each time you reverse. Go
down the string, and look for a cap with less charging current than the
others. That's the bad one.
As to the tubes -- load it into a matched load, carefully tuning for
maximum output and watch the grid current. It should stay well below
60mA, and should not creep upward. A 425 with good tubes will drive to
legal limit with 50-60W on most bands, less on lower bands, more on
higher bands.
If you need to do troubleshooting, schematics are on my website.
73, Jim K9YC
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