----- Original Message -----
From: "Carey Lockhart, KC5GTT" <[email protected]>
To: <[email protected]>
Sent: Saturday, August 11, 2012 9:43 AM
Subject: [Drakelist] hum in audio
Hello All
I have developed a hum in the audio of my t4x. on am it
completely wipes out the audio and pushes the output up. on
ssb it is there but not near as bad. you can actully
understand the audio. i have checked power supply voltages
and all is well. before i started poking and hacking i
figured it was best to seek your opinions.
Carey
Make sure this is not power supply hum by checking the
supply with an AC meter or scope. There should be little
ripple. However, I suspect that you have an audio hum due to
a loose ground. The hum will be worse in AM because in AM
mode the side-band filters are bypassed. The audio goes to
the modulator which connects directly to the output tubes so
there is much more low end. If the hum is from the audio
stage there should be none in CW. Begin with the microphone
and its cable and connector and if not there with the
connector in the transmitter. One standard bit of voodoo in
much old equipment is to go through and work and tighten all
the screws. Very often ground connections are made through
them and they become slightly corroded in the same way as
the contacts on switches do. Working them will clean the
connection and often get rid of pernicious problems.
--
Richard Knoppow
Los Angeles
WB6KBL
[email protected]
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