Thanks Dave,
Yes, you were right, that resistor was cracked into 2 pieces. I transplanted an
unused one from my 222 amp and just turned it on an hour ago. Voltages are now
same as before, no smoke, and it makes watts as before, yippee.
73,
Chet, N8RA
-----Original Message-----
From: David Olean <k1whs@metrocast.net>
Sent: Tuesday, June 11, 2024 10:24 PM
To: chetsubaccount@snet.net; yccc@groups.io; vhfcontesting@contesting.com
Subject: Re: [VHFcontesting] FW: ARRL June VHF N8RA Single Op-All Modes LP
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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