开云体育“When it comes to the switch area, that schematic is spinning my head” ? Glad it is not just me…… ? ? I have not had time to get back to this, maybe tonight. ? I believe it is in the 6V6 area because when I pull the 6SA7 the symptom remains. Maybe the choke has some leakage to ground? I was going to pull it last night and check it on my Sencore inductance tester. Got side tracked and didn’t get there. I’ll try tonight. ? Tom W3TA ? From: [email protected] <[email protected]> On Behalf Of don Root
Sent: Saturday, February 15, 2025 5:14 PM To: [email protected] Subject: Re: [HallicraftersRadios] SX-28A Hum ? Hi Jim Re paragraph 1:? ?I would not be surprised about the talking, but can that cause 120 cycle hum? Re paragraph 2: ?I agree, and there must be lots of return currents from B+ running to and thru the chassis, and chassis connections are rarely soldered, and to top it off, the schematic gives no hint as to ?the common wiring running to a chassis connection, so if one chassis connection opens a bit, what all lifts above the chassis common. After 70 years, there is lots of opportunity for corrosion. Thinking out loud about the original complaint, hum would not seem to be from the B+ into the plates,? since there is no hum in one switch position, but it might be getting into 1 or both 6V6 grids, but it would seem to be both. When it comes to the switch area, that schematic is spinning my head. ?I would probably try to poke around with a scope and a high impedance probe. So often hum comes when there is an open connection from a lower impedance source signal wire. With so many schematic connections to the plate and choke etc it is hard to speculate on the real wiring. This is likely no help at all, but I tried. ? From: [email protected] [mailto:HallicraftersRadios@groupsio] On Behalf Of Jim Whartenby via groups.io ? Don More likely that the filter inductor and the tone inductor are talking to each other.? I don't know exactly where they are located on the chassis but I have noticed that high power Peavey 8 ohm to 70 volt line transformers talk to each other when co-located.?? ? Lots of strange things happen when there is some corrosion between the mounting screw and the chassis.? Loss of a "common" connection or some weird ohmic connection plays havoc with any circuit. Jim ?
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