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  #31  
Old 07-29-2010, 07:52 PM
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My line voltage is 119.2-119.4vac. The number sort of fluctuates up and down a bit, and the longer I hold those two probes in the wall socket, the more nervous I got... lol.

I believe there's a fault with a 22 ohms resistor associated with the 1st Audio 6SQ7, or something very near to it. The closer I get a probe to it, the louder it buzzes. I think it's just boosting the signal through the air. But when the static goes dead, I can bump the resistor with the volume down and the noise comes back. I cleaned my potentiometers the best I could with a little bit of alcohol and WD-40 ( not the same day ) and I don't get all the scratchy noise so much, but I swear it seems like the tone control does nothing until you turn it to a certain spot, and there's noise all of a sudden. The volume pot does something similar, as the sound cracks in and out. It's silent, I jack it all the way up, it finally starts to crackle through.

I could swear I almost hear a signal through some of that static today...
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  #32  
Old 07-30-2010, 12:23 AM
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STOP USING OIL TO CLEAN CONTROLS!
Alot of oils have a detergent to remove carbon, whichis what is in controls!
You may have dammaged those controls now, doing that.....
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  #33  
Old 07-30-2010, 01:19 AM
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Well... I certainly hope that isn't the case here. I used very little of the WD40, just a couple drops and mainly on the outside, and I doubt very much got inside. The alcohol is 70% isopropyl and it's been a proven cleaning agent that evaporates quickly, so I used it a bit more heavily. I've noticed no ill effects.

Just to test this, I decided to soak a pair of old carbon resistors... one in WD40, one in the alcohol. I'll check up on the results by morning.
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  #34  
Old 07-30-2010, 07:50 AM
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You'll hear a lot of good opinions about control cleaners and there are fancier cleaners for sure, I've got some of them. But I have also used a few drops of WD-40 on controls for years and so have a lot of other people, and it works for me. You don't want to soak a control with any product, though. I usually use CRC Electronic Cleaner available from auto parts, and then a drop or two of WD.

You may have an intermittent resistor or control causing the set to jump from static to quiet. The heat/freeze method should show up a fixed resistor. Turning the control slowly to all of its positions while wiggling the shaft might show up an intermittent. With set off, connecting your ohmmeter between center lug of the control and to either end and then slowly rotating it should show a smooth progression on the meter, not jumping around.
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  #35  
Old 07-30-2010, 08:40 AM
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Keep in mind that the problem with pots is build-up of fluff... and some of that cruft comes from wear and tear of the control itself; which means you get carbon dust building up inside, on the wiper and track, affecting the resistance.

The idea is thus that a small amount of WD40 will get to this and remove it from the wiper path and wiper contact, while leaving the track generally unharmed- it's easier/faster to dissolve a powder than it is a solid block of something!

Yes, drenching things in WD40 won't do them any good, but a little bit probably won't hurt.
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  #36  
Old 08-01-2010, 07:40 AM
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I'm not sure what to make of my pots... I get a pretty smooth movement on my analog meter when I turn the volume control up and down, but I get so much weird static and pops out of my speaker regardless. I replaced that resistor I thought was acting up, but when I powered it up, I got this repeating tapping noise... the tap,tap,tap I've been getting lately as if someone where tapping the stylus on a record player. It taps more slowly on broadcast, and speeds up to machine gun speed on shortwave and phono.

I was getting some microphonics by tapping the chassis and I thought it might be a tube. I tapped the 2nd Audio Det A.V.C. tube ( 6SQ7 ) and got the static to pop in and out and make weird noises. Swapping this tube with the other 6SQ7 created a constant buzz. And when I turned up the volume, it's dead until halfway and then I got loud static, unchanging in volume. I turn a little louder, it goes quiet. Yet the pot seems to read fine on the ohmeter.

Lastly, something weird happened. After I powered up the radio and powered it back down a few times, trying these tubes. I put everything back in place once more and turned it back on. Nothing happened... no dial lamps, no heaters glowing, nothing. I flipped the switch back off, tried it again. Nothing. Finally I unplugged it, plugged it back up, and tried again, and still nothing. I turn the switch off, then on again... and it seems to turn on but I start hearing this "plink" sound near my transformer so I kill the power.

I feared it was either my transformer, or my 6X5 blowing and popping from the arching inside the tube. So I turn the chassis back over and power it up again just to make sure, and it powers up fine. The 6X5 is fine.

What in the world...?

Last edited by RitchieMars; 08-01-2010 at 07:45 AM.
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  #37  
Old 08-01-2010, 08:25 AM
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Power problem sounds like an intermittent in the wiring somewhere between the plug and the transformer primary. With it unplugged check with ohmmeter across the power switch turned on and off several times, check all associated wiring for continuity. Wiggle wires while checking with ohmmeter. Switch could be "iffy."

Often a "putt-putt" sound points to a bad cap. You replaced one electrolytic. The other may be "injured." Try jumping another one across it as a test. Be sure to observe + and - on these caps. The designation on the cap can be confusing. The aluminum can is the negative, and the positive is the wire coming out of the insulating disk.

Hum pickup: with volume turned up part way, you should get a hum from speaker by touching center lug of volume control, or grid of the 6SQ7 first audio.

Check all chassis grounds. Are any grounds through a riveted or screwed solder lug? If so shine them up and bridge solder between them and chassis. Sometimes corrosion gets in between the lug and chassis and makes noise.

Get the audio section working first before going on to the radio.
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  #38  
Old 08-01-2010, 08:07 PM
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I checked into the wiring around the plug and the transformer, but I could find nothing. My switch, however, does seem to be very "iffy." Testing for continuity, I found that it does switch on most of the time, but several times it fails and nothing happens. Even the way the switch "clicks" doesn't feel right at times.

I found a bad ground that had come loose, repaired it, and the "putt-putt" sound went away completely. I'm still getting static in all modes of operation, but the static is smoother and more consistent. With the volume control, I can only make the static loud, or practically non-existent. I can't vary the volume of the static with the volume control. It just simply isn't there with the volume down, then at about 1/3 turn it pops in, stays there until the last 3/4, and goes away. With volume turned max, the set is quiet.

I do get plenty of buzz from probing around the volume control and the 6SQ7. From left to right, looking at the pot from the bottom, there's a green wire, a black wire, and a bare wire with a 30k resistor which runs to the 6J5 2nd audio. I get the loud buzz from the green one, which goes to the 6SQ7, pin 2.

I'm a bit concerned about the popping, plinking sounds I've heard from my transformer. When I turned it on again today, I heard the same popping sounds I heard last night. They go away quickly, but since I can find nothing else at fault, it makes me worry that the transformer is suffering from internal shorts as a result of it's overheating in the past. I do have a replacement in mind... but I'm a bit fuzzy on how to replace it... but that's another story.
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  #39  
Old 08-02-2010, 09:51 AM
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The popping and plinking may well be the tubes expanding and contracting from warm-up; I know my set will occasionally "plink" when cooling down.

Regarding the static; if your volume has a loudness tap, check the components coming off of that; that could explain the appearance in the "middle" of the range.
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  #40  
Old 08-02-2010, 01:03 PM
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Don't think your xfrmr is at fault if it only gets warm and not hot, doesn't sputter and fry, voltages are normal on secondaries, and voltage from either side of HV to center tap are essentially equal. Look where the wires go into the xfrmr shell: look OK, not frayed?

Might be able to get the switch limbered up if you can get some cleaner in there. If not, might have to replace the volume control/switch. Sometimes they can be carefully taken apart and worked on.
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  #41  
Old 08-02-2010, 10:00 PM
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RitchieMars RitchieMars is offline
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I wouldn't say any of the wires are frayed... but I can't say they're in great shape. In fact, a couple of them look rather burnt.



That bare wire coming out of the transformer seems to be some kind of ground, I believe. That big white wire is a temporary power cord to the phono, by the way. I've been wanting to buy some vintage-style wires but the only place I know that has them doesn't take PayPal, and since the wires are sort of pricey, I've used whatever I had around for now.

Last edited by RitchieMars; 08-02-2010 at 10:05 PM.
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  #42  
Old 08-03-2010, 06:47 AM
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That grounded bare wire is an interwinding shield. From what I can see the wires look OK, not old and cracked. The black stuff is potting tar from the xfrmr. A lot of times over the years some leaks out normally.
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  #43  
Old 08-03-2010, 07:50 AM
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Have you checked your plate resistances on rectifier?
Looks like socket may have been arcing.
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  #44  
Old 08-16-2010, 08:47 PM
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Well, I haven't messed with this thing in a few weeks but I went back and checked everything and I can't find anything troublesome other than the 6SQ7 tubes. With the two original tubes installed, I get a loud buzz as I turn up the volume. When I switch out the one nearest the volume pot for a newer 6SQ7, it causes the static in the middle of the range. I only get static with that one tube and I get a buzz with the others.
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  #45  
Old 08-17-2010, 06:18 AM
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I'd try putting the one back in that allows static, and, get some good control cleaner, and, try cleanning the volume control. See if that soves that problem.
What is the model of the set, and, tube line up?
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