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RCA X551 Humming

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Post by 75X11 on Tue Sep 09, 2014 6:00 pm

If you have a replacement, it wouldn't be too difficult to replace the socket. If you hace a pop rivet tool and small rivets with washers for the rivets to act against as opposed to the plastic wafers alone.
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Post by jerryhawthorne on Tue Sep 09, 2014 6:15 pm

75 has a good point on pop rivets.  Only get aluminium ones.  Steel require too much force to "pop".  Even with a washer underneath.  Most of the time I just go to ACE hardware and pick up some nylon screws and nuts.  Don't look original from the top but no worry about the metal washers from the pop rivet needed underneath getting close to some Hi voltage.  Especially on a rectifier.  The ones I did really did not have room to get a pop rivet gun in, yours appears to have room.
Good luck,  Jerry

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Post by Dr. Radio on Tue Sep 09, 2014 10:13 pm

Frank,

Welcome to the school of hard knocks. It's mandatory attendance and we've all been thru there!

I pulled up my Beitmans schematic on your radio. Your radio doesn't agree 100% with the schematic, but it appears it is not your fault, but some factory revisions.

Here's things to check on (verify your connections):

Pin #7 of the 35W4 is the rectifier output. It should connect directly to the (+) side of the 33 uF electrolytic. This pin should also see a direct connection to the red wire of the audio output wire.

Remember, when I say "direct", I mean there is a wire or connection, it doesn't "pass" thru another component. If you take your meter and read ohms from the points I say, you'd see zero ohms.

Where does that 33 ohm connect? What pins of what tube? I'm guessing that was a surge resistor originally before being omitted later.

The brown wire coming out of the audio output transformer should connect directly to one side of a 1200 ohm resistor. The other side of that resistor should connect to the + side of your 47 uF electrolytic capacitor. The + side of the 47uF cap should also have a connection to pin 4 of the 50L6 tube.

RCA used this design a LOT in which the primary of the audio output transformer is used apart of the filtering circuit to clean up the pulsing DC from the 35W4 and negate hum.

Now, let's check those negative connections of those electrolytics.

Both need to go to B-, NOT chassis ground. B- is easy to find, it's the lug on the power switch which connects to the other lug (that has one wire directly from the wall outlet) when you flip the switch.

Obviously, the connection points I called out make "other stops" and connect to other components, but check things over and let us know.
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Post by Dr. Radio on Tue Sep 09, 2014 10:18 pm

Red wire of audio output transformer

(I meant to say that above)
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Post by frank1956 on Wed Sep 10, 2014 1:12 pm

ALL, Radio is working. It was a simple fix and something I over looked. Double checked the filter cap's as suggested and found the neg was incorrect. Fixed it and no hum, stations come in loud and clear cheers . No alignment is required all volt reading are within tolerance. Thanks for the help/advice. I'll see if I can pick up another one this weekend lol!

RCA X551 Humming - Page 2 100_4070_zps34fcd480
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Post by Bill Cahill on Wed Sep 10, 2014 2:15 pm

I'm familiar with that radio. Though simple, it's a good performer.
Congradulations..........

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Post by Wildcat445 on Wed Sep 10, 2014 2:39 pm

Congratulatins, Frank! Glad to hear you fixed it. cheers

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Post by frank1956 on Wed Sep 10, 2014 2:45 pm

All, might have spoken to soon!!! The radio does play, picks up what stations that are close by, but after about 20 min or so it fades out, not for long about a min or two. When it fades out just white noise, once the stations come back it loud and clear. Any idea of what might be causes it? (Alignment)
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Post by Dr. Radio on Wed Sep 10, 2014 3:05 pm

Worst case scenario is issues inside the IF transformer(s).

Best case scenario (start here) is intermittent solder joint, bad component etc. examine the solder joints on the two hottest running tubes first---the output tube and the rectifier.
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Post by frank1956 on Wed Sep 10, 2014 4:59 pm

Dr Radio, Checked the solder joint's as suggested found both needed attention took care of it, but still same same. Thanks for the advice.
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Post by frank1956 on Wed Sep 10, 2014 5:40 pm

Here is a video of what the radio sounds like when it fade in and out.

Frank

https://s1259.photobucket.com/user/relichtr/media/WP_20140910_002_zps95ad5ca2.mp4.html
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Post by Bill Cahill on Wed Sep 10, 2014 5:46 pm

It could be IF transformer trouble, or, a tube shorting out, since it goes in, and, out. Normally, bad IF transformers just go out, and, stay out. My guess is a bad tube, or, maybe a dirty tube socket. Try wiggling the tubes. If that doesn't do it, try lightly tapping the sides of each tube.

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Post by frank1956 on Wed Sep 10, 2014 6:13 pm

Bill thanks for the advice. I clean the tube sockets prior to installing the tubes, I also checked each tube on my tube tester and all were within spec's. I did wiggle the tubes and did notice some tubes fit loosely in the tube socket, but it did nothing to the radio to cause it to fade out.

Frank
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Post by jerryhawthorne on Wed Sep 10, 2014 6:31 pm

Frank, I have to say I have never had a radio that sounded like that! Time for more fun and some real troubleshooting. I believe you have a signal generator, is that correct? If so you could set it to your IF frequency and turn on the modulation for a tone. Hook it up to the grid of the first IF tube. Fire up the radio and you should get a strong tone. Leave it running to see if the tone goes in and out. If it doesn't, your IF and audio section is dandy. If it does drop out and back in we can narrow it down a bit further with further tests. Next would be to set your generator to tone only for testing the audio.
Let us know how the first test goes.
Your really having some fun now!
Best, Jerry

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Post by frank1956 on Wed Sep 10, 2014 8:08 pm

Jerry, Yes I do have a signal generator. So I am to connect to the first IF tube 12BA6 pin 5?
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Post by jerryhawthorne on Wed Sep 10, 2014 8:17 pm

Frank, about to climb in the car and take off for a 6 hour drive. Hopefully some one can chip in. Checking on you in the morning.
Best, Jerry

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Post by Wildcat445 on Thu Sep 11, 2014 10:53 am

Since the hash stays all the time, I would suggest that you look for a bad connection somewhere. A guess would be that any bad connection would be ahead of the IF section. The audio and the power supply appear good. Maybe take compressed air and clean out the tuning capacitor real well. Check the antenna connections. Maybe sub the 12BE6 and/or the 12BA6. If the tubes appear loose in their sockets, you could squeeze the socket terminals together with needle nose pliers to make them tighter. Good luck.

WC

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Post by frank1956 on Thu Sep 11, 2014 12:13 pm

WC, Thanks will check that out. When you say that any bad connections would be ahead of the IF section am I working toward the speaker? i.e 12AV6, 5OL6 tubes???
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Post by Wildcat445 on Thu Sep 11, 2014 1:11 pm

Working toward the speaker, yes. Start with the antenna. I seem to have problems with those old RCA antennae. Then check for crud in the tuning cap. I have had a spider web short out the tuning cap in the past. While you are at it, gently blow the dirt off the entire chassis. Double check connections, as has been suggested before. Sub those two tubes I suggested with ones out of the Silvertone. Just see if anything like that makes a difference. Boy, Frank, how lucky can you get to have TWO intermittents in a row? Are you sure there is not an enviromnental hazard somewhere like a power line situation or something like that causing problems in your radios? I had to have the power company out here. I not only live in a fringe area, but we had really "dirty" power lines. I showed their engineer on my scope how much interference I had. They changed a transformer, and that cured my issues. Good luck.

WC

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Post by frank1956 on Thu Sep 11, 2014 3:04 pm

WC, Funny you should mention the power lines. I live right next to a power sub-station, power lines in the front and back of my house. Just curious as why my other tube radios are not affected?? I will attend to the issues you mention above - the power line for right now. Thanks

Frank
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Post by 75X11 on Thu Sep 11, 2014 4:13 pm

I don't know if you have cable in the house, but the powersupply for, and the cable converter box I use, puts a horrible ac hum across the entire midrange of the dial. I have to disconnect it from the outlet for my units to work well. Lights with dimmers get noisy as well.
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Post by 75X11 on Thu Sep 11, 2014 4:18 pm

I was also going to suggest that you clean the audio input jack, as it appears that it can isolate the radio's AF signal from the audio amplification portion of the radio.
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Post by frank1956 on Thu Sep 11, 2014 7:58 pm

Here is another video I did. I have moved my work area to a different part of my house. The one I was using had my computer, modem and printer might have been interfering with my testing. Any way the intermittent problem is still there, but I don't think as bad as it was. When back and checked/corrected any solder joints, clean the tuning cap, clean underneath and ensure all tube sockets were clean/tight. Swapped out some tubes from the Silvertone I was working on previously. I can not seem to get a lot of volume output, I have notice if I get near the antenna board the volume increases confused . Thanks



Frank
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Post by 75X11 on Thu Sep 11, 2014 8:24 pm

I don't have a copy of your schematic, but if it is a station whose volume is increasing, you might want to see if the antenna coupling cap might respond to a small adjustment. move it no further than you can get back from.
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Post by frank1956 on Thu Sep 11, 2014 9:54 pm

http://www.nostalgiaair.org/PagesByModel/948/M0015948.pdf
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