Recapped the Admiral! - Still having issues...
 

Awhile back, I had talked about my Zenith television and it became clear to me at that time that I should start by learning to work on my radio's first. So, I did finally work up the nerve and read up on it and bought the capacitors I needed to do the Admiral and my Zenith H724. The Zenith came out fine, louder and seems to pick up stations better now that I've added an external antenna. The old Admiral, however, remains problematic.

All of the wax paper capacitors and the electrolytic capacitors in my great-grandmother's 1942 Admiral 4215-C7 are new and installed according to the factory schematic. Trouble is, I had to swap out the rectifier tube with another 6X5 out of a derelict chassis I had sitting around to get it to work. This rectifier tube worked fine for awhile until today when I let the set warm up, the tube suddenly got bright and went out, arching and whatnot. I'm not quite sure if it's simply that the tube was already going bad, or if something inside my chassis is wrong and caused a short. The electrolytic caps associated with this tube are both 20uF and I know that I could have safely went with 40's. It did have a slight buzz when you turned the volume up, but it was a louder buzz when switched to phono. While the set did run, and I allowed it to warm up and run for periods no longer than 10 or 15 minutes at a time, and I did notice that the rectifier tube and the output were both rather hot. Up to this point I was almost able to pick up radios signals, but I had to squeeze wires to the antenna loop with my fingers to actually hear anything, even with the volume all the way up.

I had a replacement audio tube ( 6SQ7 ) on the way because one of the two seemed to glow very weakly, but now that doesn't matter since my rectifier went out... =( Any ideas?

Just to give you a general idea of what I'm dealing with, my Admiral's tube compliment includes a 6X5GT as the rectifier, a 7A7 as the IF amp, 6SA7 1st Det. Osc, 6SQ7 2nd det. osc, another 6SQ7 1st audio, a 6J5GT as the 2nd audio, and then a 6K6GT as the output tube.

How bright a tube filament glows is usually not important. Some are dimmer than others by design and work fine. 6X5's can be problematic if there's a heater to cathode short. You may just have had a bad tube. Before you plug a new 6X5 in there you want to look for any excess load in the B+ circuits of this set: any partial shorts to ground or resistors in the plate circuits of tubes that have dropped in value (usually they go up.) Some tubes will get very hot, too hot to touch, in normal operation, but their plates should never glow red which means they are drawing too much current. How does the transformer feel under load? It may get quite warm, but not so hot you can't put your hand on it.

Also be certain that electrolytics are connected correctly with respect to polarity.

With two 1N4007 silicon diodes, you could operate the set without a 6X5 for testing purposes. The cathodes of the diodes (end marked with a band) would go to the tube pin where the tube cathode was connected, and the other ends to the plate pins.

I couldn't find the schematic for this set on the web but if it has a loop antenna, both wires to the loop have to be connected to complete the tuning circuit. The fact that stations were very weak may just be because someone played with the alignment of the set before you got it. Sometimes a person will "tighten all those loose screws" on the I.F. transformers and the tuning capacitor in an attempt to "fix" the radio.

Yeah, I only figured that one dim tube may have been faulty because the other which was the identical type, was a bit brighter. Even when switched, the dim tube remained dim no matter which slot it was in. I don't have a tube-tester yet so it was all guesswork. The bad rectifier was much more obvious, and the first one was causing the transformer to start getting hot as the set warmed up. When I swapped that 6X5 out for another, it ran fine. All the tubes simply glowed orange at the very top, the rectifier and the output tubes were the hottest and brightest but no glowing red plates anywhere. The transformer at this point would only get just slightly warm on top, and I could feel this sort of vibrating quiver coming from it whenever I touched it or turned the knobs on the front of the radio. I've never actually "felt" the current running through one of my radios so I didn't know if that was normal or not.

The weak reception probably was partly my own fault, as I do recall trying to turn at least one of those screws back about a year ago when I first pulled the chassis out for cleaning. I'll have to go back and realign everything once I'm sure it's running like it should be.

Here's a scan of the schematics I acquired, although there is a few minor differences I've noticed. For one, my tone control is the on/off switch rather than the volume knob. The radio had a lot of repair work that I had to sort out which included an added Mallory 2x8uF wired parallel as a 16uF which was used to replace one of the bad 20uF's in the multi-section can. All that's done away with now, of course. I don't much care for the cheap-looking hand-painted resistors, either.

You want to be careful with that rectifier tube, as a shorted tube (or any other short in the B+ line) can fry the power transformer. Your 6X5 could have failed on it's own; or, it could have failed due to an excessive load somewhere in the radio. Since you changed all of the capacitors; you'll need to make sure there are no frayed wires that are touching the chassis or other parts. The same goes for any component leads. Also, make sure that no solder balls or any other conductive objects are in the chassis. I'd also suggest placing a fuse in the center tap of the HV winding on the power transformer. A fuse on the order of 250-500 mA should work. Most of these old radios were not fused and a fuse would have saved many a power transformer.

This set was made at a time when the industry was changing from older style resistors to the striped ones familiar today. The older resistors were a bar of resistive material with wires wrapped around the ends and were all factory painted like those in your radio, and are read "B.E.D" or Body, End, Dot: the body color is the first digit, the end the second digit, and the dot is the multiplier.

I've heard that there was a rectifier tube that was failure prone, with heater-cathode shorts. Think it was the 6X5, but I'm not sure if that was the one.

And how bright a tube heater looks to be doesn't really indicate the health of the tube. It depends partly on how much and how close the ends of the heater wires are to the end of the cathode pipe, some tubes the heater wires stick outside, some the ends are inside the pipe. Has no real impact on how hot the cathode inside where the grids and plate action is.

"I've heard that there was a rectifier tube that was failure prone, with heater-cathode shorts. Think it was the 6X5, but I'm not sure if that was the one. "

I think that is the case... I have read of numerous 6X5 failures (mostly shorts). Restorers seem to favor the "X Plate" design.

http://www.antiqueradios.com/forums/...64698e2acbeb0c

jr

Yup, 6x5 tubes are known for this-I had one fail on a Zenith. When they go, they can take out the power transformer-best to get your set fused. Your set should play really well once it gets aligned. Did it have a built-in antenna inside of the cabinet?

The way some get around the 6X5 problem is to wire a couple of silicon diodes under the chassis and put a dud 6X5 tube in the socket for show, disconnecting the appropriate wiring to the tube. This has the additional benefit of reducing the heater load to the transformer.

I recently had a 6X5 blow out too - just like you described. I replaced it with diodes as suggested and it's working fine now :)

Wow, I would have never had guessed that this set used a tube that was faulty by design. I would like to get a NOS 6X5GT, but if I can't trust it then I guess I would rather get those diodes instead. It sucks since the vacuum tube design is what draws me to these radios, and in this case it seems like I'd have to make at least one small concession for reliability purposes. The diodes are certainly way more affordable than the tubes. I rather like the idea of using the diodes and keeping the tube installed with the heater glowing just for looks. How would I do that? Or, would it be best just to leave it out all together?
http://tubedata.milbert.com/sheets/127/6/6X5GT.pdf ( 6X5GT )
Referring back to my radio's schematic ( 3rd post in this thread ) why is it that pin 1 isn't even mentioned? Several pins in my radio have wires running to them that aren't covered in the schematic. Isn't it leaving out the path that heats the filaments?

I think if you fuse it properly you can still use one without fear of blowing the xfrmr. Here's some food for thought: http://antiqueradios.com/forums/view...&highlight=6x5

I've had a crazy idea for a while. Remove the base from a 6X5. Wire in a couple 1N4007s to rectify and a red LED to simulate the filament. Then remount the base and no one's the wiser ;)

Hm, that "Copper Cap" tube replacement is pretty neat. Much pricier than the diodes, of course. I can get those diodes AND a NOS 6X5GT for under $7. I think I'll get some fuses and resistors while I'm at it. I really would like to simply run the set with the 6X5GT, but I know for a fact this transformer has had a few close calls already. It got toasted once before by the first bad rectifier and the bad capacitors, and it started to overheat slightly the first time I tested it right after I recapped it. Then I put in the 6X5GT and it ran well until the other day minus weak reception. The same RCA I borrowed that tube from has a compatible transformer if need be, but I'd hate to have to take that thing out and sort out the wiring on such a vital component.

I've got those diodes on the way but I've also read about putting a dropping resistor to keep the B+ from going up? A guy in one of those threads mentioned a 6X5WGT which seems to be a military grade 6X5 and it's an X-plate like those that are generally regarded as the best variation. I might like to consider that option in addition to fusing my transformer which I should do with either option, I would think.

Revisting all of the 6X5 discussions over on ARF, I think I'd go with diodes and just leave the rectifier heater glowing for looks. If my transformer were running hot, I'd leave the 6X5 heater disconnected. With diodes, as long as the B+ measured at tube plates is within the tube ratings as determined from a tube manual or a lookup site like

http://www.nj7p.org/Tube.php

you should be OK. If you need to drop voltage, just figure by Ohm's law. From tube data, add up the plate currents of all the tubes, figure how many volts you need to drop, and R = E/I. Then to figure the size of the resistor in watts, P = E x I. I would double this wattage rating to make the resistor run cooler.

As to tube socket terminals not shown on the schematic, sometimes a particular terminal is not used on a tube. That leaves the socket terminal free for the manufacturer to use as a tie point in the wiring.

Thanks, I'll be looking into all this once my diodes arrive! At least it's shaping up like the Admiral will live to play again, 50 years after it fell into disuse. It's literally been half a century since anyone in my family has so much as seen the dial lamps light up or heard any music out of it.

The only things I'm left searching for are the cosmetics. I've found a grille cloth that's nearly an identical match to the original. That'll be a big improvement. The knobs are all original and look a little warped... but other than that okay. The only other "big" thing I'm missing is a dial pointer. I can't find anyone who has a listing, an image, or anything about this radio online. Only google results you'll find is my threads in this forum and at AK, and replacement dial lenses. I'm not sure who to turn to in search of dial pointers, nor can I can I find a reference image to give me an idea of what mine should look like.

Hey guys, I think I've figured out a big part of my problem! It all started when I asked some guys over at AK about my 10-inch speaker and someone pointed out that what I likely had was an "electrodynamic" speaker and sure enough, that's exactly the case. I looked into this and found that running a radio such as this with the speaker disconnected put's a burden on the first electrolytic capacitor right after the rectifier as a result of the speaker's field coil being absent from the circuit. Most testing I did involved the speaker being plugged in, but the last time I ran the Admiral, it was without the speaker just to poke around and see where my B+ voltages were looking like. I powered up the radio only twice in this manner, and on the second attempt was when the rectifier blew.

Going back my chassis recently, I discovered that my first 20uF filter cap is SHORTED! Apparently, it suffered under the heavy load and since that capacitor goes straight to ground, it's understandable why the rectifier went when it did. If I am to understand this design correctly, there would have been the possibility of a rare "perfect storm" scenario. Consider the possibility of a broken speaker wire, or a shorted field coil, a filter capacitor with a tolerance no greater than 350 ( mine was a 450 and still died! ) and the known defects of the 6X5 tube... and what do you have? A dead filter capacitor, a dead rectifier, and perhaps even a fried transformer. Yikes!

So, I'm in for a new 6X5 ( maybe just for looks ), some fuses, a new 20uF electrolytic, a Y2 safety cap, and some resistors and perhaps a couple spare caps to fill out the minimum order. I'll let you know how it turns out!

Well, I'm making progress as of today but I still don't get what's going on. I replaced the shorted electrolytic cap, and since my capacitors should all be good now, I went about replacing a few resistors. Found a couple that were way off. I have four variants of the 6X5 tube; the first type with two rows of plates, the second and slightly smaller GT version, the X-plate GT version, and the military spec Raytheon WGT. I've been testing using GT, and I'll be leaning towards the X-plates for longer periods of use. No problems there.

I've install a Y2 line filter cap and that dulled down a lot of the buzz I was getting before. Now I only get a soft buzz when the volume is all the way up, just like on a cranked guitar amp. No noticeable hum, but there is static that comes through the speaker intermittently. I get it when I turn the volume and tone dials. I had it switched to phono earlier and could still hear the crackling here and there, even if I don't touch the tone dial. Not sure what's up with it now but I haven't picked up any radio stations on Shortwave or Broadcast.

I'm debating on where to turn next. I'd like to test it with an MP3 player connected to the phono input. There's a brown and a black wires coming from the cartridge which go to a terminal. The brown side has a ground coming off of it to the chassis of the record player itself, and the brown and black wires go together in a cord running to the plug that connects to the radio's chassis. I have some headphone wires with an appropriate plug for the MP3, but I'm not quite sure how I should go about connecting between the record player and my radio.

Spray some WD-40 in the can's cap and use something like a toothpick to drip a few drops inside the volume and tone controls where the three terminals are on them, turning the controls back and forth many times as you do it. Also put one drop where the control shaft enters the threaded bushing on the front of the chassis.

Put one drop on each of the moving contacts of the function switch and turn it back and forth a number of times. Try not to get any (or much) on the insulating wafers of the switch. The switch will also have a mechanical detent that keeps it in each position. That could use cleaning and a little spot of light grease.

This should get rid of the scratchiness of the controls.

If you switch to phono and then touch the center pin of the phono jack you should hear a loud hum from the speaker. If so, you could test with your MP3 player. Unplug the wire to the record player.

You need an RCA plug to go into the phono jack on the chassis, or you could use a patch cord with alligator clips on one end and a plug for your MP3 player on the other and hook up under the chassis. The center lead of the cord goes to the center pin of the jack, and the outer (shield) of the cord goes to chassis.

If the adjustment screws of the IF transformers and the tuning cap have been played with, about the only way to get the radio aligned would be with a signal generator. If you know someone in town with one, good. If not, check back. I gotta 'nuther idea.

Alrighty, I'll check up on these pot's and try getting the scratchiness out of them. When you said to spray WD-40 in the can's cap, do you mean to spray in the top of the IF cans? I get what you mean about the pots, though. I already had sprayed a bit on the outside of the chassis up front to loosen them because that time my rectifier got bright, my on/off switch was so tight the knob slipped off when I tried to shut it off. I've just been thrown off by the static I'm getting out of nowhere all of a sudden. I watch it run and hear static even when I don't touch anything.

Yeah, I looked into signal generators awhile back and realized that they are generally quite pricey and the cheap one's on Ebay ( old one's ) are said to be inaccurate.

WD-40: just spraying from the can to the control would get too much in there. What I mean is to take the lid off the can and spray some into the lid as a container, then dip from the lid with a toothpick, etc. You could even dip with the red tube that comes with the WD-40. There are fancier control cleaners but this works OK for me. No, don't spray anything into the IF cans!

Did you clean the tube pins on this radio? Put WD-40 on pins with a Q tip, then plug tube in and out of its socket several times while the pins are wet. Often clears up static problems. Do this first.

Okay, here's my Rube Goldberg idea for finding out if the IF section of your Admiral is tuned correctly. This is going to use another operating radio that you know has a 455 Kc IF section.

These superhetrodyne sets convert any incoming signal to an intermediate frequency (IF) and then amplify it in the IF stage. The stage consists of the input IF transformer, the IF tube, and the output IF transformer. The only signal that ever goes through there is supposed to be 455 Kc (or KHz, if you must!)

So if we inject 455 Khz into the Admiral's IF stage, and get nothing from the Admiral's speaker, then the IF transformers are maladjusted, the tube is bad, or there is some component problem.

The admiral IF tube is the 7A7. If you scratch a piece of wire on pin 6 you should get some scratching out of the speaker, meaning the tube is probably alive.

We can use another operating radio with a 455 Khz IF section as a signal generator to get the Admiral IF stage on the right frequency. If you have another tube set with such an IF, it would help if you could give the make/model and track down the schematic. And don't shock yourself if the other radio is AC/DC. :nono: Yikes. Do you know the precautions?

First, pull out the 6SA7 tube. It's not needed for IF adjustments using this method and could just cause interference. Turn the bandswitch to broadcast band.

Take a piece of insulated wire not more than a foot long and tape the ends of it, don't want any wire showing. Place one end of the wire near the plate connection of the other radio's IF tube. Hold in place with a wooden clothespin, whatever, insulated method. The other end of the wire will go alongside of the wire going to pin 6 of the Admiral 7A7, hold in place. There is no direct connection, just transfer of the signal by proximity. The wire insulation is like the dielectric of a capacitor, it's really a capacitor transfer.

Tune the operating radio to any station and then turn its volume down so you can't hear it. Turn the volume up on the Admiral and if the IF is adjusted right, you'll hear the station from the other radio on the Admiral's speaker. If you do or if you don't, try adjusting the trimmers on the second IF transformer (the one between the 7A7 and the 6SQ7) for loudest signal. If the signal is too loud to hear a pronounced peak, uncouple the wire a bit farther away from the 7A7 grid. Take it as far away as you can and still hear a tiny signal. A weak signal is best for peaking.

Now move the wire from the 7A7 grid to proximity of the wire from pin 3 of the 6SA7 socket and adjust trimmers on the other (first) IF transformer. Make the signal as weak as possible by moving the wire away from the 6SA7 socket and go over both sets of IF transformer trimmers again to find the best peak on the weakest signal.

If you get this far with signals coming through, take the wire away, shut off the other radio, and plug the 6SA7 back in. There may be stations heard, whether strong or not, whether at the right place on the dial or not. Then we'll trudge on from there.


¡Whew! Report back, trooper. :yes:

Hey, Reece. I spent some time today going over this again and I was finishing up some work I had planned weeks ago, but I was waiting on my parts to arrive. Yesterday and today, I installed the line filter capacitor, replaced a capacitor that had tested as shorted, and replaced any resistor which seemed out of spec. There were actually quite a few, and by more than 20%. A couple had doubled, and even tripled in value.

I couldn't figure out my pots. I looked for a hole to drip the oil through, but they seem pretty closed up. Here's what they look like...

http://img826.imageshack.us/img826/1542/img0925.jpg

http://img821.imageshack.us/img821/7137/img0926l.jpg

I only tested the radio once today, and I never heard any static turning the knobs around. The band selector/phono switch has no static, either. Just a soft thump when I switch it back and forth. When I turned it on, I actually heard a repeating thump when tuned to a certain spot on Shortwave. After about a few minutes of it running pretty quietly, that static came back which crackled and roared, even on phono and even if the knobs aren't turned at all.

Not sure if I have a tube bad or not, but it gives me the impression that something's causing static once the radio heats up for a few minutes. I also noticed that I get about 28 volts AC from the chassis to ground whenever the set is plugged in now. I hope I got the line filter capacitor right...

http://img191.imageshack.us/img191/1166/img0928o.jpg

I installed it as I could best understand from what I read on JustRadios. It's connected directly to the "hot" side ( small side of the plug ) and then to ground, which in this case I used the unused ground terminal.

Anyways, I'll try checking around that 7A7 tube tonight and see if i get some noise from pin 6 as you mentioned, and I think far as alignment goes, I'll probably have to pull apart my Zenith H724. I have a schematic around from when I recapped it awhile back. It doesn't pick up AM extraordinarily great... there's lot's of noise over every channel... but it's probably the best choice. I also have a Zenith K731 but I can't get the knobs off the front to get it open.

Thanks, and I'll keep checking back on this thread. I spent about 4 hours today working on that chassis, so I'll probably take a break for awhile tonight!

A quick update:

Before I went to bed, I got brave enough to test some voltages with my new Cen-Tech multimeter. Here's what I got:

6X5 Rectifier, Pin 8 ( schematic = 340v ) 364v on SW and Phono, 374v on KC
6K6 Output, Pin 3 ( schematic = 245v ) 295v on SW and Phono, 309v on KC
6K6 Output, Pin 8 ( schematic =19v ) 23v on SW and Phono, 25v on KC

I take it these are higher due to the higher line voltage we have nowadays. It was listed as 117v on this schematic.

I did this after cleaning all the pin sockets and I found that I do indeed get a little scratchy sound if I touch something to Pin 6 of the 7A7. I still got the static about 2 minutes after I turned it on, then it got worse, then it faded, then it came back!

Oh, and holding the probe anywhere near the 1st Audio 6SQ7's Pin 2 causes a buzz that gets louder if you get closer to it. Just found that interesting. I should be able to attempt an alignment soon, providing this static will keep to a minimum.

Use your multimeter to test what voltage is coming out of your outlets (set to AC voltage! Don't want to trash that new meter too quickly....) if you are getting something like 125-130vAC that could be enough to bump those voltages up a little, especially around the rectifier. I am listening to a '35 Atwater Kent right now, and when I did a cursory check of the voltages, B+ was a bit higher because of the higher line voltages, compared to what this thing was designed for in '35 (115vAC).

Which meter did you get? The $3 cheapie or the $17 "supreme" model? Don't forget, NEVER try to test resistances while the radio is under power-it probably won't kill you, but it sure will destroy your meter. Don't ask how I know this!

I bought the same model you told me about, the Cen-Tech P37772 with about 30 functions on it, I believe.

I took these measurements just now with the Admiral turned off but plugged in.

24.5v AC from the Admiral's chassis to ground ( ? )
1.5v AC on terminal that corresponds to my plug's small end where my line filter cap is installed ( see the photo above )
119v AC on the other terminal, which corresponds to my plug's larger end

Edit: I checked some other voltages later with the set turned off, and the primary winding of my transformer is putting out exactly 120v. But, I checked my heater pins and they're showing 7.9v AC. Isn't this a bit high for the heater voltage? Is that what's driving my B+ through the roof?

Well, so much for my attempt at aligning the Admiral. I get my Zenith apart and get everything ready, and the Zenith's AM goes dead. I put it back where I had it, hooked up the external antenna and still nothing. Now my Zenith is just static and a few pop's and crackles just like my Admiral. I was picking up stations pretty decent on AM just earlier tonight.

Even after I replaced the wax capacitors, I'm pretty sure everything else in my Zenith is about done. It has worked well the few times I've used it of lately, but it's started to have some crackles and pops for a minute or two which would clear up after a few minutes. I tested a couple of resistors just awhile ago and found a few that were a pretty good bit off. There's a bunch of bubbly ceramic capacitors and a big "black beauty" cap, one of those marked with colored bands. It also has one of those weird selenium rectifiers. Things are a bit difficult for me to reach in that tiny little radio, so I don't particularly look forward to working on it again. My Admiral is very roomy and much cleaner in comparison.

Well, there's still the K731. I haven't checked to see how it picked up AM...

It doesn't have to be a "vintage" radio to use as a signal generator, just one that has a 455 kc IF. Maybe there's another radio in the house? Just wrap the wire around the IF tube in that radio to pick up its signal or else stick the end of the (insulated) wire down inside the second IF transformer.

The static may be from a faulty resistor. Get a can of computer keyboard cleaning "air." Wait for the static, then work fast: turn the can upside down and use the extension tube on the can: freeze each resistor in turn and see if freezing one of them makes the static stop. Check by letting it heat up again to make static and then refreezing.

Yeah, I think this could be an issue in both of my radios. I have every resistor on hand for my Admiral, and so far I've replaced 6 of them. I also have the mica capacitors. Haven't replaced any of those... wasn't sure if I needed to. What do you make of this higher heater voltage I'm getting? 7.9v? Could there be something wrong with my transformer? I'm worried about running it anymore this way because last time, my 6X5GT went out in a flash and I've looked into it and found that they shouldn't be operated above 7.5v. But... I've noticed that the two dial lamps are bridged between the two heater pins. One is the correct type 51, and the other is type 44 for some reason. Would this throw off the filament voltage?

I also think there's something up with my volume knob. I tested it using my analog meter and from the bottom up, the needle rises as it should, but about 3/4's of the way it slumps back down and rises slightly again. But, the volume itself does seem to increase as it should through the speaker, yet the static itself changes volume.

When this radio was built, voltages were probably listed as tested with an analog multimeter. Today, line voltage is higher, and the meter you are using is more sensitive and loads the circuit less, so you will typically read higher voltages. The voltages you listed earlier are reasonable. Are you getting 7.9 volts with all the tubes plugged in and heaters glowing? That does seem a bit high but don't think there's anything wrong with your transformer. If turns were shorted you'd get lower voltage and the xfrmr. would get toasty.

With set turned on and no tubes plugged in you will get higher heater voltage. With all tubes plugged in, the voltage should come down to close to 6.3 AC, maybe a bit higher allowing for higher line voltage. Set your meter to 200 volts AC and stick the probes in the wall socket. What's your line voltage?

Did you do the freeze test on resistors yet? No need to replace all the resistors in the set. I almost never have a bad resistor, or only one or two.

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...

STOP USING OIL TO CLEAN CONTROLS!
Alot of oils have a detergent to remove carbon, whichis what is in controls!:no:
You may have dammaged those controls now, doing that.....
Bill Cahill

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.

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.

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.

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...?

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.

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.

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.

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.