re: SB-220 cap arc and the local 10kw broadcast station
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Hello again,
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I had also witnessed an SB-220 tank cap flash over
problem, in an otherwise stable amplifier I rebuilt
some years back (had my own suppressors installed).
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Turned out to be the Cap as mentioned below. I
found out by asking on Amps that Heath had
changed the cap to a higher V rated unit. Speculation
by some that the cap change was done to deal with
the yet undiscovered parasitic issue.
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I purchased a replacement late version cap from Carl
which went right in, problem solved. I have the original
"snapper cap" right here (still), the part number appears
to read 26-145 (although the "5" is almost unreadable).
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I tried all the cleaning, de-burring type tricks before I
bought the late version cap. In my opinion, lack of
proper parasitic suppression and an otherwise eager
capacitor caused the previous owner (two different
brands of) tube failures.
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The amplifier tank would "snap like heck" during key
down (full drive, SSB Position) . The late version
cap is in, the amplifier is in regular service with no
additional problems.
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*************
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Before I did the complete rebuild, the SB-220 into
a well shielded termination/load would take out
the 90.3 signal into the FM Broadcast Receiver on the
other side of the room.
The receiver blocking was quite the eyebrow lift
as the 10kw FM transmitter is less than a mile
from my office.
-
After the standard updates were in place (which
include my own type of suppressors), full tilt key-
down into the load didn't even touch weak signals
into the adjacent FM receiver. Sometimes the
music stinks, but it's not the amplifiers problem...
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Life goes on...
cheers
skipp
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[snip]
--------- Forwarded message ----------
From: Pete Smith <n4zr@contesting.com>
I replaced the Measures suppressors in an SB-220 with two conventional
suppressors I bought from KM1H, and power output on 10M increased about
100
watts. The amplifier, which was quite well built by whoever the original
assembler was, is unconditionally stable. I can, however, make the plate
tune cap arc by typical contester stupidities like transmitting into no
antenna, the wrong antenna or having the loading set much too light for a
given antenna.
73, Pete N4ZR
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