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.
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 between the winding and core or frame in the original. A sensitive ohm meter would probably tell. I had thought of suggesting putting the old choke on an insulator (just a sheet of paper) temporarily to see if the hum stopped. Not worth taking the new choke out to try. The SX-28 is an interesting receiver, an attempt by Hallicrafters at advanced engineering that didn't quite come off. The Lamb noise blanker was a very good idea but was not well implemented. Eventually, Drake and others, did a better job with it. This type of blanker works well on pulse type noise, like ignition noise, but hardly at all on the more common (now) power line noise. Hallicrafters eventually published a modification (on BAMA) to disable it and replace it with a conventional series limiter. I hope not many SX-28s were mutilated this way.
On 2/19/2025 11:57 AM, thoyer via groups.io wrote:
Yes, I replaced the original CH2 with another 4hy one I had from an R390A AF module.
On Wednesday, February 19, 2025 at 02:43:41 PM EST, Richard Knoppow via groups.io <1oldlens1@...> wrote:
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.
