Bad Hum in RCA Record Player.. PROBLEM FIXED

I have an RCA 45rpm 8EY4 Deluxe record player that I totally recapped about a month ago, and I've been playing it often. Yesterday, I turned it on and it has a terrible hum...even with the volume control turned all the way down. I suspected a bad tube and pulled the tubes and checked them on my tube checker. All four tubes test very strong with no shorts. What could cause this? I would think if something in the amp was going to break down it would do so before a month of using the player. The set has a tube lineup of 35W4, 12AX7 and two 35C5's.

You guys got any ideas?

Larry,
Recheck the filter caps, maybe replace them again. If that doesn't work bring it to the house. I'll take a look at it.

John

I'm going to pull the amp tonight and have a close look to be sure an electrolytic is not grounding out and also check solder joints closely.

Problem is fixed. The 7HF45 has the same tubes as the 8EY4 Deluxe, so I opened the 7HF45 and started substituting tubes. The 12AX7 and 35W4 tubes were fine. When I substituted the first 35C5 tube, the hum was gone.

Thanks, guys for all your help. Now I know a tube can cause just as bad a hum as a bad electrolytic.

Filament-Cathode short...

What kind of tube checker do you have? It should have shown such a bad short like an H-K leakage.

Lou,

The tube "checker" was a tube swap I believe. Probably the best tube checker out there...

I have a tube checker, a Heathkit checker, and it tested that tube super strong with no shorts.

Tonight I ordered a couple of NOS 35C5's and a 35W4 from AES just to have some extras on hand.

I just don't think a tube checker always catches this type of problem.

Larry,

Yes, substitution is the ultimate tube tester. But some of us have tubes coming out of our rear ends and others have only those tubes that are in the actual piece of equipment. I have some extras that I use. But I do test them. H-K shorts are known to cause hum. And those high filament voltage output tubes are working hard and bet very hot. They also have lots of filament wire wrapped back and forth inside of the cathode so it is not impossible for it to fail.

As noted, most of the time it is a open filter capacitor. But since that problem was already addressed, the next logical place to look would be the output tube(s).

Most importantly, glad you got 'er running! I have a 45-EY-4 and it sounds amazing. Don't remember if it is PP 35L6 or 35C5. And I don't know if they made both, maybe not. I know that Bill Cahill will know...

Any Heathkit should have found that bad tube, has your tester been refurbished? At what point does it start to indicate a short, you may have a bad resistor in the short test circuit.

Dave

Don Cavey wrote:Larry,

Yes, substitution is the ultimate tube tester. But some of us have tubes coming out of our rear ends and others have only those tubes that are in the actual piece of equipment. I have some extras that I use. But I do test them. H-K shorts are known to cause hum. And those high filament voltage output tubes are working hard and bet very hot. They also have lots of filament wire wrapped back and forth inside of the cathode so it is not impossible for it to fail.

As noted, most of the time it is a open filter capacitor. But since that problem was already addressed, the next logical place to look would be the output tube(s).

Most importantly, glad you got 'er running! I have a 45-EY-4 and it sounds amazing. Don't remember if it is PP 35L6 or 35C5. And I don't know if they made both, maybe not. I know that Bill Cahill will know...

The 45EY4 has a pair of 35L6GT output tubes, whereas the 8EY4 Deluxe has a pair of 35C5 miniatures.

Thanks! I have not taken mine apart. I actually bought it in working condition. It does sound very good...