[Drake] TR-4 Hum

[Byron Tatum]

Hello-
    If anyone can help here I would be most appreciative :
        I have a later model TR-4 { plain TR-4} and RV-4 combo.After I =
had been using it for several months I noticed a fairly loud hum on all =
bands except 80 and 20.  I ruled out the AC-4 supply and filter cap in =
the TR-4 itself, I know these are good. I suspect something in the =
pre-mixer, however the hum is only present when the RV-4 is plugged in. =
Without RV-4 plugged in there is no hum on any band. The TR-4 and RV-4 =
are well bonded with ground braid. I replaced V-1 pre-mixer tube with a =
known good 6EA8. The hum dis-appears when I pull this tube out of its =
socket. I did notice that the hum became stronger and more erratic as I =
moved my fingers around the tube.
    I tried a second, similiar TR-4 and when connected to RV-4 it did =
not hum. So I do not suspect the RV-4 itself. So I feel the problem is =
in the radio itself, and only occurs :=20
                                                1.When the RV-4 is =
plugged in.
                                                2. Only on 40, 15, and =
10 meters {bands that employ pre-mixer}
        HELP someone please!
                                            Thanks, WA5THJ.
     

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