I recently received a few reports of some minor distortion
while using AM. Running the stacks program I discovered that the voltage measured at the finals at full output (using stacks program) was showing 12.4V, while the power supply was solidly set at 13.8V. In made a heavier power cable using 10 Ga copper wire, and also applied a small amount of conductive silver grease to the power connector, and to the internal fuse contacts. 12.4v now measures 13.1v and the distortion is gone. Since Flex does not provide a schematic for the 6500, I have a few questions that I’d like to have Flex answer.
1. I’ve read that Flex uses a high side current sense resistor. Between that and the power cable it’s normal to see at least a 1 volt drop between the finals and the power supply. Is this true?
2. I’ve also been told that Flex themselves runs the supply voltage high enough to produce 13.8V at the finals, as measured by the stacks program. How high can the power supply be safely set to?
3. For an 8ft power cord run, is 10 Ga stranded copper wire adequate?
By the way, after doing the above on those bands where my max output was ~85W, it’s now easily producing 100W.
A1 1 volt sense resistor drop makes no sense as that would be 20 watts at a 20 amp draw.
A2 answer in the h/w manual.
A3 measure V drop across cable length and decide if you can live with that. I use a #10 8inch cable long to minimize drop.
I see Jay types a lot faster than I. Sorry for the double post...
At 100% power, key down, FRStacks shows my voltage as 14.1v, 96watts. into my 50ohm dummyload, which may not be an accurate 50 ohms. I can get a better match using my antenna, and see a little over 100watts.
For real-time discussions
73, Jay - NO5J
In my opinion the version of the Anderson power-pole connectors found on many HF radios today are not heavy duty enough.
When the warranty runs out on my 6600M I will be replacing the power connector with a Neutrik PowerCON type power connector. Super heavy duty locking power connector.
So, I previously reported that I was seeing as much as a 1.4-1.5v drop from the power supply to the measured PA voltage using FRStack software. I started looking into this after receiving some reports of minor distortion while running AM. With the power supply, set to 13.8V, was measuring 12.4-12.5V at the PA. For the record, the power supply itself was rock solid – less than .1v drop at full power. The distortion and the excessive voltage drop is fixed – here’s how I solved it.
I needed a 6-foot power cord. To minimize any voltage drop. I wanted pure copper, something heavy, yet very flexible. This stuff is great, a 4” piece will flop over like a we noodle! I made a new cable using the 45A rated Anderson connectors to accommodate the larger 10Ga wire – thanks to Dave WO2X for the connectors! They were crimped and soldered.
Next, I carefully inspected the main fuse in my 6500. I found a very light amount of a brownish discoloration on the forks. I cleaned that up with some 3M Scotch Brite and very sparingly applied a tiny film of the conductive silver grease below to the 30A fuse blades just behind the power connector in my 6500. Once applied I inserted and removed the fuse a few times. While I had the radio open I did the same for the smaller 3A fuse on the other side of the radio. I also sparingly applied the conductive grease to the Anderson power connector on the radio and on the cable, which I honestly feel was the weakest link in this problem.
Finally, I readjusted the power supply to 14.2V (measured at the power supply). I used FT8 to provide some constant power transmissions at 100W. FRStack now shows 13.8v, sometimes up to 13.9v
Flex should consider applying a dab of this grease to the fuses and the power connector.