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I am not sure that the problem is resolved.? CH2 was replaced with a similar value choke with less winding resistance so it will have higher Q.? Higher Q will affect the audio filter curve so there

Greetings to the Group: I attempted to replicate Emanuele's measurement of the RF tank circuit.?? This required that I construct an RTMA dummy antenna, which turned out to be a bit of a chore; I

In one test, I removed the original choke from the chassis, still wired in place though and still had the hum so connection to the chassis makes no difference. Tom Sent: Wednesday, February

Hello Emanuele, Did you see any part number on the Main Tuning Capacitor (C7) ?? It should end with 341… As you seems to have a LCR meter, can you also measure C7A (the section of the main

Emanuele Real good pics! The knowledge that it looks original helps reduce speculation that it has been modified and that is causing the problem.. good to know about that. The trimmers for band 4

Don, no idea about the run of this unit. The serial on paper is almost impossible to read; looking carefully it seems read "serial. 196479". No other info. Here is an info briefing: As arrived, the

Hi Scott, Talk about timing... I have an SR-160 (upgraded to SR-500), an SR-400, and matching P-500 power supply that I would like to find a good home for (all in good working order and

Hi Scott, Talk about timing... I have an SR-160 (upgraded to SR-500), an SR-400, and matching P-500 power supply that I would like to find a good home for (all in good working order and

Thanks Jacques, well that seems to pour cold water on the magnetic coupling theory. If the trace I copied is typical {I don’t know}… ie; assuming that hum is 60 cps with third harmonics at /I n

Thank you. Since its a different choke it doesn't explain why the original was humming. Doesn't matter if the problem is solved but would be interesting to know. Its possible there is a leak

In a SX-28A, the CH2 is as far as it can be from the power transformer: The black “core” at the left is the CH2. You can see the bottom of the power transformer and the filtering choke

Yes, I replaced the original CH2 with another 4hy one I had from an R390A AF module.

Please clarify, do you mean you replaced the original choke and the problem went away? If so it could confirm my idea of filament current somehow coupling through the chassis. -- Richard

Tom, if I recall it was not fastened to the chassis… at least in the same way. If the power transformer is near by the choke, it’s flux can/might use a bit of the chassis and the choke could

Interesting Don........ When I replaced the choke, CH2, this all went away so I don't know how it would be related to the power xfmr? Tom

Tom and/or anybody still tuned in. Still looking for what really failed and how. For anyone wondering about the details and possible source, I copied a bit of your first Video so I could take a

Hi Scott, The Tornado (SR-500) is an excellent tri-bander. It is a single conversion receiver that performs better than a lot of dual conversion rigs. With its 250 to 300 watt output it will punch

Excerpt from?https://www.chavfreezone.me.uk/2023/sx28.html.? Might want to read the entire article. There is also an underlying very low-level hum present which is totally independent of audio

Jim,? You are correct. I had replaced the choke but with 12" leads outside the chassis. There was a reduction in hum but it was still there. This time I installed it in the same location as the

Richard,? The choke is held to the chassis with two screws that have internal tooth lockwashers on both sides - one under the screw head, one under the nut. That is how it was when I removed it and