Chet
I would bet that a 100K dropping resistor has opened up and that will
remove any B+ voltage from the zener diodes in series that make up the
screen voltage. The power resistors are big 100 watt units and have a
habit of opening up. They are located in the HV sub assy of the
AM-6154/6155. You can get away with just one dropping resistor..
Dave K1WHS
On 6/11/2024 5:34 PM, chetsubaccount@snet.net wrote:
ARRL June VHF Contest - 2024
Operator(s): N8RA
Station: N8RA
Class: Single Op-All Modes LP
QTH: FN-31
Operating Time (hrs): 3
Summary:
Band QSOs Mults
-------------------
6: 37 17
2: 16 10
222:
432: 11 9
-------------------
Total: 64 36 Total Score = 2,700
Club: Yankee Clipper Contest Club
Comments:
A few years ago, we owned a sailboat and every spring after un-winterizing it,
we would take her out for a shakedown cruise to see if all its systems were
well for the coming season. Since my VHF/UHF station had not been used since
January, I took a few hours Sunday afternoon to start it up and see if all was
still OK.
I went first to 432 and that worked well. The band seemed in good shape, and I logged
several nice Q’s including a 400-mile one.
I then switched to 222, and that did not seem to be working. I heard no
activity, even on my omnidirectional stacked loops. I tried CQing a bit and
then set it to listen for FT-8 activity when I went to dinner, but NADA heard.
Something is not right so it has made the to-do list. I suspect a feedline
issue since the SWR was a bit high.
I then fired up 2M and it initially was working FB, until,,, suddenly I was not able to work anyone.
I’d call a strong station, get no response, and they would CQ again in my face. A glance at
the wattmeter showed zero watts out! Checked computer audio, Win 10 updates, N1MM logger, WSJT-X, or
if the transverter had tripped out, but no, those were all OK. The 2M amp is a converted old FAA
AM-6154. Plate voltage was OK but it had zero screen voltage- uh-oh! This amp was converted for me
by K2ERG about 12 years ago. I’ve run it conservatively and it has served me all this time
without a hiccup. But now it’s made the to-do list. Bummer.
Lastly, I went to 6M to see how that gear was working, and had a lot of fun
there; All was well on that band.
73, tnx for the Q’s, and I apologies if a 2M QSO with you went away abruptly.
Chet, N8RA
PS.
Yesterday I pulled the power supply module out of the 2M amp, and as expected,
the screen voltage dropping resistor (100K 96 watts) is open circuited. Did the
higher duty cycle FT-8 in recent years do it in? That seems unlikely since it
is always energized. This is a unique flat resistor to fit the limited space
inside the HV PS module. and seems to be now unavailable. Argh!!. What to do?
Build an external screen voltage supply? Add an external doghouse for a larger
replacement resistor? Deep 6 the amp and move on? Today my brain reminded me
about having shorted out one of two of those resistors as un-needed in similar
amps that I had converted for higher bands years ago. Sure enough, I now have a
good resistor for repair.
Posted using 3830 Score Submittal Forms at: http://www.3830scores.com/
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