|
Thanks Jim, will look into those areas. Tom
On Friday, February 14, 2025 at 09:04:50 AM EST, Jim Whartenby via groups.io <old_radio@...> wrote:
Look at the audio response curve in the manual.? With the BASS switch IN, the low frequency audio is emphasized, not attenuated.?? The BASS switch in the IN position shorts out two components, CH2 and C43, I would look there first.? Perhaps there is AC being coupled into the audio circuit via CH2?? Check that the mounting screws for CH2 are making good contact with the chassis,? Corrosion between the screw head and chassis could be the problem so loosen and then tighten them.? Might as well do the same for any screw that supplies a ground or chassis connection for the audio circuit in that area of the chassis. Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Friday, February 14, 2025 at 06:10:04 AM CST, thoyer via groups.io <thoyer1@...> wrote:
Good idea, but I pulled V12, 6SC7, and the hum remains. It is definitely in the output stages Tom
On Thursday, February 13, 2025 at 08:10:23 PM EST, don Root <drootofallevil@...> wrote:
Tom Good for you Presumably, the base “In” position filters out the hum as expected… And the hum comes from upstream, maybe the AF gain? Pot area or a bad contact in the phones switch, or even before that. ?? ? From: [email protected] [mailto:[email protected]] On Behalf Of thoyer via groups.io
Sent: Thursday, February 13, 2025 7:22 PM To: [email protected] Subject: [HallicraftersRadios] SX-28A Hum ? I just finished pretty much a complete overhaul of a nice condition (physically) SX-28A. Replaced just about every resistor and all caps. ? Radio is working well except for a 120hz hum. When I switch the Bass in, the hum goes away. ? Yes, there is ripple on the plates of the 6V6’s, about 6vrms, but that is there independent of the bass switch position. The output side of the HV filter is clean, no ripple. I paralleled another 47uf 450v cap across the choke input cap and there was no difference. ? I double checked the wiring against the schematic along with component values. Is the schematic correct in this area? I found once schematic error maybe there is another? ? Thoughts? ? Tom W3TA -- don??? va3drl |
