HO-10 Monitor Scope

[Steve Harrison]

At 06:57 PM 1/30/99 -0500, DonaldF F Christensen wrote:
>C-31 in my HO-10 has gone bad. C-31 is a 0.15 mfd @ 1600 volts. The
>closest I could come in my junk box was 0.047 @ 1600 volts. I wonder if
>the 0.015 could be a
>replacement for the 0.15 or is it too small? Any one know where I can
>find a new
>0.15 @ 1600 volt tubular capacitor? Thanks for listening. 73 Don W8WOJ

Go ahead and try the 0.047; there may be a little less HV but I bet you
could hardly measure it. For sure, the 0.015 is way too small to replace a
0.15 mF.

Just make certain that the leakage current on any replacement caps you try
is very low so you don't overload that rare and impossible-to-replace power
transformer! The day is coming when there will be more of us with blown
transformers than working Heath Station Monitors/Panadapters. Somebody
hereabouts was asking about getting quotes to have such transformers either
rewound from bad cores or as new items; whoemever that was, how about a
short update??

I would be tempted to install a single strand of the smallest wire I could
find as a fuse between the secondary winding and the rectifier circuit,
although I've heard that the more common failure mode of the transformer
involves internal insulation (or lack thereof) breakdown. But you need to
consider the inductive kickback that could occur when the wire suddenly
opens: I think there's a real possibility of the kickback causing a very
high voltage spike that could initiate arc-over within the transformer!

Along these same lines, I noticed just yesterday that both the Mouser and
James Electronics catalogs have small HV power supplies for use with xenon
flash tubes and the like (a bit too high-voltage, however, at a few kV,
apparently; but maybe run at reduced input voltage??). Made me wonder if
there isn't some way one of us cannot design and produce a small HV power
supply to run from the filament winding to replace open HV windings on
these transformers.

Come to think of it... if Mouser and James have those HV PS kits, perhaps
they also have suitable HV caps? I didn't think to look and the catalogs
are at work.

Also, someone recently did mention another source of the caps, perhaps from
Mouser or another similar vendor.

73, Steve Ko0U/1

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