RCA 6K Puzzle

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RCA 6K Puzzle

Post by Timaaay! on Tue May 05, 2009 2:34 am

Greetings to all! I'm writing to ask for help with my RCA 6K. I restored this radios several years ago and use it in my workshop as my daily driver. It's got great sound and terrific bass. Anyway, about a year ago, while listening, the volume would suddenly get REALLY loud, the volume control still worked to raise and lower the volume, but even with the volume all the way down, it was still fairly loud. Turning the radios off and on again would return it to normal. It may happen in an hour, a day, a week or more, but always happens. I removed the chassis, checked all the connections by tapping and prying with t plastic tool and could not get it do it. I cleaned all the tube pins and sockets and put it back together. It seemed fine for a few weeks, then the same problem. A few weeks ago, I took the chassis out, replaced the volume control and changed-out all the tubes. I ran it for two weeks out of the cabinet and it seemed fine. I put it back together and used for a little over a week and then, tonight same problem. It's definitely not a bad connection as I re-soldered almost every joint and banged the chassis and every connection. It's not a tube or the volume control.
When the volume rises, it goes quite high with no static or rumble whatsoever, it's as if someone threw a switch. Turning the radios off and on again always returns it to normal. Does anyone have a clue what else may cause this problem? I've done and checked everything I could think of. I even hit all the connections and parts with -50 spray.
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Re: RCA 6K Puzzle

Post by Resistance is Futile on Tue May 05, 2009 2:57 pm

If your light dims Then this may be of interest.
This is from CASE HISTORIES in Radio Troubleshooters Handbook.
"RCA 6K-2, 6G-10
Intermittent____1) small rivet in center of band pilot light cutting off of signal and dial light "SHORTING TO GROUND""
And my own opinion (LOL) a resistor or CAP value may be changing due to heat, since it seems to work out of the cabinet.
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Re: RCA 6K Puzzle

Post by Neon27 on Sun Aug 01, 2010 7:00 pm

I've experienced this problem with some Valve radio sets.

Depending on the atmospheric density i.e. clouds and atmospheric pressure; radio station can drift ever so slightly. Depending on the weather around you and the broadcasting station, the radio station signal can be amplified, attenuated or drift in frequency. All these factors can result in your radio station sounding extremely loud or soft at times.

I do suspect though that you have an electrical problem inside your radio set.

I actually have a Bendix radio set which does EXACTLY what you described. Firstly, I did a quick fixer-upper job in re-tuning the IF stages. Secondly, I haven't got round to replacing the old capacitors and resistors, I only replaced the capacitors which were 100% damaged. My educated guess is that some of the original capacitors & resistors heat-up with time, and as result, drift the local oscillator frequency. The mixers & IF stages are quite resilient with some frequency drift (valve radios drift a lot in nature), but sometimes the drift is significant enough to attenuate a station (de-tune from a band), or tune right into it. In the case of your radio, it might be mixing incorrectly or poorly filtering the desired station in the IF stage. In the cases when the volume gets very loud, it could be your radio is actually working, and tuning into the band!

If it were my radio, I'd re-solder ALL joints. Some 'dry-joints' are untraceable. A thin layer of oxidation can often form between a pin and the solder around it.
Secondly, I agree with the above poster: replace all your paper caps. In fact, I'd replace all my resistors too. There's no shame in it. Just be prepared to re-calibrate your radio after changing some components, you'll find the newer resistors and caps may differ in value from the original ones (even if they're rated the same, tolerances of older parts are poorer)

Best regards,
Eddie
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Re: RCA 6K Puzzle

Post by denver on Mon Aug 02, 2010 11:14 pm

Most likely a cap . I had this problem was a mica cap changing value . When i turned it off then on worked fine for about 20 minutes cap would loose value . Was hard to pinpoint this problem. Most micas keep their values good but sometime find a bad one. Good luck. Very Happy
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