Dave
Long shot but your comment about it might be stray rf Struck a cord.
1) I would try the amp on 80M if you dont get the flash over then there
then this adds credence to that theory.
2) A beefier bypass cap at the DC end of the new RF choke is likely in
order. The stock.SB220 only had a .001uf there If I recall correctly.
My TL922 (which covers 160M with a pair of 3-500Z's has a .002) there..
Dave
NR1DX
On 12/13/2019 11:12 PM, Dave G. ve9cb@rac.ca wrote:
Hello all:
I am looking for some advice on some arcing I am seeing in the B+ supply of my
Heathkit SB-220.
I never used the amplifier before I bought it at a flea market in Spring 2019.
I have modified the amp to add 160m, following Rick Measures' (AG6K) excellent article in
January 1989 QST. Among the many things I did ti the amp, I replaced the stock
Heathkit plate choke with the plate choke used in Ameriton amplifiers (part number
10-15197. I thought was a better way than to winding my own choke.
I now get 600w out of the amp on 160m with about 80w of drive on the Low B+ position
(2kV). I run the amp from a 110vac, rather than 220vac. It will ultimately be
used in a remote location where only 110vac is available.
While keying in CW. I see sparks and flash-overs about 25% of the time. These
flash-overs are between the leads of the filter caps in the B+ supply and the
chassis wall of the amplifier.
I suspect stray RF is the culprit. I believe the Ameritron plate choke is
sufficient, because it is used in all Ameritron amps that include 160m.
So, what should I do to eliminate this arcing? Would adding a layer of insulation
on the interior wall of the chassis opposite the filter caps be enough? Is this
just applying a band-aid to cover up a more serious problem?
I have not tested the amp on other bands to see if it happens there, too. The
primary use of this amp will be for CQ 160m CW contest operations from Labrador
(VO2).
73,
Dave VE9CB
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Dave
Manuals@ArtekManuals.com
www.ArtekManuals.com
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