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Post by cricket on Oct 2, 2010 21:34:45 GMT -5
I recently received a Tram D201 that has an audio hum when I increase the volume and decreases when turning the volume down. No hum at all with the volume all the way down.
Also, the hum is much louder on sideband and doesn't receive anything on sideband, no RX noise etc. It does however receive stations in the AM mode.
So far I replaced the HV power supply filters and re-capped the BA board and still no change. It now appears to rule out the Power Supply.
Any ideas??
Many Thanks.
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Sandbagger
Administrator/The Boss 
Posts: 6,250 
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Post by Sandbagger on Oct 3, 2010 12:02:06 GMT -5
I recently received a Tram D201 that has an audio hum when I increase the volume and decreases when turning the volume down. No hum at all with the volume all the way down. Also, the hum is much louder on sideband and doesn't receive anything on sideband, no RX noise etc. It does however receive stations in the AM mode. So far I replaced the HV power supply filters and re-capped the BA board and still no change. It now appears to rule out the Power Supply. Any ideas?? Many Thanks. It its day, the Tram D201 was one of the finest performing CB radios ever made. However, its design does not lend itself well to a long life. The way the radio was designed it puts a lot of stress on several 2 watt carbon resistors, which will drift value and may also eventually completely open. Then there are the electrolytic capacitors which also will fail with age. It's certainly possible to restore one to its full glory, but it will require a lot of part replacement and some other clean up work depending on whether it is a PC board version or the point to point wired version. I restored 2 of them for my own stable (and a bunch more for others). Both of mine had hum problems which was mostly due to bad filter caps on the power supply and a bad front end receiver tube on one of the radios. SSB receive was out on one and that turned out to be an open power resistor in the SSB IF stage. Your best friends when working on a radio like this are a volt meter and an oscilloscope. |
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Post by don19488 on Oct 12, 2010 12:36:57 GMT -5
Probably not a power supply issue, if it were i would expect to have the hum at a near constant level. Try looking in the audio section,at the tubes and maybe even the volume control. Try subing the audio tubes for known good ones,and of course as far as checking the tubes, you will need access to a mutual conductance tester,as all the emission testers do is basically a no load look at amount of emission. Good luck. warlock35po
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