[VHFcontesting] FW: ARRL June VHF N8RA Single Op-All Modes LP

David Olean k1whs at metrocast.net
Tue Jun 11 22:23:40 EDT 2024


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 at 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/
>
>
> _______________________________________________
> VHFcontesting mailing list
> VHFcontesting at contesting.com
> http://lists.contesting.com/mailman/listinfo/vhfcontesting



More information about the VHFcontesting mailing list