This looks suspiciously like there is still some reactance in the antenna system Paul. If it's anything these amplifier types can't tolerate it is reactance in the output. It does seem that way Steve
No. I'm not sure of anything! I'm a HF/VHF/UHF and tube amplifier guy who decided to get on LF. Working with FETs and ferrite is all new to me. 9t to get 50uH suggests ferrite witout a gap. IN which
Hi Andy, This is very interesting, because 12 watts is what I think I have consistently been able to generate into the antenna before problems creep in. I can easily accept that this amplifier may on
Hi Andy, Thank you very much for that. I am learning and knowledge sometimes comes together from bits and pieces in discussions like this. Anything is possible with this amp or the filter. I tried wi
The plot thickens! The square wave isn't exactly symmetrical but by that calculation it makes no more than 8 watts into the dummy load without the filter! It's likely a bit more because it isn't symm
I think Chris has some really good ideas here. I did turn a test with the dummy load at the far end of the coax the other day. The amp didn't seem quite as happy as with the dummy load in the shack b
I had a thought. I set the HP 3325B to 10V pk-pk, ran it through the scopematch into the dummy load. Scopematch showed exactly the expected voltage and indicated 50 ohms, no reactance. Next I inserte
Hi Marco, I don't detect any heat in the LPF but at this low power level it could be difficult to detect it. I already have plans to build the big T type LPF. I have the T-225A-2 cores and metal to m
Hi Clemens, Thank you for taking the time to run these simulations! My Ultimate 3S does have a LPF before the feed to the PA. I understand some PAs prefer a square wave. Should I remove the LPF? I ha
I was able to make a few more tests without getting frostbite. :) I disconnected the coax from the matching transformer (at the antenna) and put the coax into a dummy load. All OK, exactly the same a
During the night I made a few more tests... Iso xfmr at PA output. 14T:14T on FT-114-JC core. Made the problem slightly WORSE. Iso xfmr at amp input. 4T:4T on 3 x BN73-202. Made the problem slightly
One final thing. Thought maybe something in the antenna was breaking down (arcing or corona), so made another check: I now have the capability to run the PA on 13V or 19V. At 19V I can make more powe
Hi Chris, At PS side of the choke, no RF behaving or misbehaving. At output transformer side of the choke, mainly negative-going pulses which become distorted similarly to the output when misbehaving
Hi Clemens, OK, I understand about capacitive coupling in transformers. So I tried a simple common mode choke. At first 22 turns using RG-178 coax on a FT-114-JC (yes, made a typo last time). No chan
Hi Markus, Could the scope "blurring " be caused by a high-frequency rather than low-frequency oscillation? It's possible but what I see is not what I would expect in that case. My experience has usu
Thanks Andy. Assuming by driver stages you mean what is external to the PA, the exciter. This is one reason I tried driving it with the function generator (HP 3325B) instead of the usual exciter (QRP
I have been operating JT9 and CW on MF the past two nights. Easily worked VE7SL at 4048km. I have one, maybe two more nights before I must QRX to bring the variometer inside due to bad weather. I kno
Dave, Currently the weather forecast looks good for being QRV Wednesday into Thursday, but I will have to update this status tomorrow. Forecasts can change. If not this time, perhaps I can work you n
I was forced to stop calling CQ on JT9 at 2320 UT when my PA again became unstable. This is the same dual band PA I am having so much trouble with on LF. On MF it will make about twice as much power
On 01/03/2018 06:43 AM, DK7FC wrote: Am 03.01.2018 00:37, schrieb N1BUG: I was forced to stop calling CQ on JT9 at 2320 UT when my PA again became unstable. So it is a thermal problem!? Sure seems so
