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Drake TR-4 "hum" when transmiting SSB

Nov 17th 2013, 17:03


Joined: Nov 3rd 2013, 22:07
Total Topics: 0
Total Posts: 0
I have been aff the air for the past 15 or so tears. I am 74 years old. I decided to get back into the hobby I loved since 1954. I got the TR-4 on the air to work the November SS this weekend. I did pretty well for an old man and an old rig with a G5RV antenna between 2 ttes. But, out of hundred or so contacts, about 7 or 8 told me I had a "hum". Can anyone suggest what might cause this hum? I amnot realy very technically inclined. Thanks
Nov 18th 2013, 18:42


Super Moderator

Joined: Apr 4th 1998, 00:00
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Total Posts: 0

You may have a bad audio cable, which will cause hum in the audio. To check for this, press the PTT button and listen on another receiver with the RF gain turned down sufficiently. If hum is present, disconnect the microphone and key the PTT line with a jack and a clip lead (use caution, only do this with one hand behind your back). When keyed with no microphone, if the hum goes away, the microphone cord is defective, or possibly the microphone itself is bad. Try another microphone. Get another local ham to listen to your signal, if possible.

The other cause of hum would be if your High Voltage filter (electrolytic) capacitors in the power supply are tired. Try sending in CW mode, with the key held down for a few seconds (use a dummy load so not to cause interference) and listen on another receiver. If the note is not pure and has a flutter or ripple to it, the HV capacitors need replacing.

Or, your old Drake just doesn't know the words......

Bob Allison
ARRL Test Engineer

disconnect your microphone and see if you can manually key the PTT line. While keyed, listen on another receiver with the RF gain turned down sufficiently.

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