Hum in RCA 45HY4

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Hum in RCA 45HY4

Post by Guest on Sun Feb 22, 2009 5:14 pm

My RCA 45HY4 has developed a low fluttering type hum, even with the volume control all the way down. It had absolutely no hum after it was totally recapped. I suspected a bad tube as the culprit, so yesterday I substituted a complete set of four good tubes from another player that has the same tubes. Still, there was no difference.

What could cause this hum?

Help me out guys.

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Re: Hum in RCA 45HY4

Post by Tony V on Sun Feb 22, 2009 6:04 pm

Caps? Even some new caps will fail prematurely. Ground issue? Dirty muting switch? Cold solder joint?
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Re: Hum in RCA 45HY4

Post by Guest on Sun Feb 22, 2009 7:41 pm

I suppose it could be any of those things. I'm going to open her up and take a close look.

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Re: Hum in RCA 45HY4

Post by MinnesotaHam on Sun Feb 22, 2009 9:11 pm

Trying grounding the signal grid of the 12AX7 then the 35C5 tubes. Might be able to isolate the hum to one stage of the circuit this way.

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Re: Hum in RCA 45HY4

Post by Guest on Thu Feb 26, 2009 10:32 am

I don't know how I fixed it, but it's fixed. I opened up the chassis and tapped on the top of the chassis with the rubber end of a screwdiver to see if any solder beads or other conductive debris might be lodged in the wrong place somewhere, then I subsituted an entire set of different tubes and there was no difference. I found one cap in the tone control circuit laying against the chassis, so I pulled that out a bit. When I re-installed the original tubes, the hum seemed to be gone. Now I can't hear the hum a foot away from the player. Now if you put your ear right up in the speaker, you can hear a very slight hum, but that's normal. I think it must have been the cap against the chassis causing the hum problem.

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Re: Hum in RCA 45HY4

Post by Bill Cahill on Thu Feb 26, 2009 1:48 pm

You had a B+ to chassis short, shoring it to cartridge.
That with coupling capactior from B- to chassis, you were also loading power supply.

By the way, read my post on your phono in ARF.
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Re: Hum in RCA 45HY4

Post by Guest on Fri Feb 27, 2009 2:05 am

Bill Cahill wrote:You had a B+ to chassis short, shoring it to cartridge.
That with coupling capactior from B- to chassis, you were also loading power supply.

By the way, read my post on your phono in ARF.
Bill Cahill

Bill, I believe you are right.

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