Recapped the Admiral! - Still having issues...

[RitchieMars]

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.

[RitchieMars]

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!

[RitchieMars]

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.

[Reece]

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.

[RitchieMars]

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.

[Reece]

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!

[Reece]

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. 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.

[RitchieMars]

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...





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...



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!

[RitchieMars]

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.

[leadlike]

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!

[RitchieMars]

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?

[RitchieMars]

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...

[Reece]

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.

[RitchieMars]

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.

[Reece]

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.