After replacing the filter caps and equalizing resistors, I fired up the 76A today on 40m and had a couple of nice contacts. The 120hz hum problem *appeared* to be gone. The spectrum analyzer showed
Perhaps it doesn't know the words? :) -- Best regards, Chris Wilson. mailto: chris@chriswilson.tv _______________________________________________ Amps mailing list Amps@contesting.com http://lists.co
Jim, it is possible that the hum is present only in your local receiver and not actually being transmitted. As a test, you might have a local listen to the signal and give you a report. 73, Gerald K5
Is this into a dummy load? Is the amp grounded? Carl KM1H After replacing the filter caps and equalizing resistors, I fired up the 76A today on 40m and had a couple of nice contacts. The 120hz hum pr
On 10/17/2013 6:22 AM, TexasRF@aol.com wrote: Jim, it is possible that the hum is present only in your local receiver and not actually being transmitted. As a test, you might have a local listen to t
Jim has isolated the problem to the amplifier. He has operated the amp into a dummy load with still the same problem - but only on 160. He has had others listen and hear it and also used a different
Thanks, Colin. Since it's the only one standing, I'm going with your theory. This isn't a known (or heard of) issue with the design, so I'm going to choose to assume that there's a component failure
If you are observing the signal on a spectrum analyzer or receiver inside the ham shack near the amplifier by picking up the field near the amp it may not be there at all. If you have an antenna on t
Hi Bill, I know what you mean about hum modulation on the power line and local receivers, but this is strong enough that it almost wipes a transmitted SSB signal out mixing with it, and CW signal is
Are you running AM on the other bands too? If it's not there (or not strong) on SSB, I'd suspect filter cap(s) in the HV string. I don't work AM, but on CW, I've had exactly that symptom, with exactl
Hi Jim, Yep, we tried AM and SSB both. The filter caps are brand new, and I also changed the bleeder/equalizer resistors, as well as the other carbon comps on the control board, since they were drift
I'm guessing a bit here.....but the numbers should be 'ballpark'. The 'cold' end of the plate choke is bypassed with maybe a total of around 5000pF to ground. That's about -j17 ohms. The plate choke
On AM Ive found that GIGO is often the reason for hum. A bit of PS ripple in the xcvr that isnt noticable on CW/SSB is pronounced on AM. Lots of older rigs have leaky caps; Kenwood in particular with
I agree, Carl, but I doubt it's the case here. The hum peak at 120Hz from center is only 6dB down from the carrier when driven at 1805 kHz, and 14dB down at 1995 kHz. It's not a "little bit" of hum.
FYI, for my 80m/160m duoband amp (2500V, three GU-74Bs), below the "main" 200uH plate choke, I'm using a supplementary 62 uH choke wound on a ferrite core and bypassed at the cold end with a Sprague