GE A-66 new refurbish job - Page 9 - Videokarma.org TV - Video

leadlike · #**121** 03-06-2010, 09:29 PM

Ah, you replied while I was typing. Those voltages are just fine. Your radio appears to be basically functional now. Have you hit the bandswitches and volume/tone controls with cleaner yet?

de.facto7 · #**122** 03-06-2010, 09:42 PM

yes.. cleaned with denatured alcohol.

de.facto7 · #**123** 03-06-2010, 11:07 PM

a question...

There's a dogbone resistor marked 50K that is across a couple of terminals inside the housing of the 1st IF. I have had to replace all but 1 of those underneath the radio as they were more than 20% over tolerance. Though measuring it without clipping it isn't the most accurate way to test it, it's showing 44K ohms which is under tolerance. If it's a 10% it's off the mark. If it's a 20% I guess it's OK. Should I replace it or leave it alone?

Thanks...

de.facto7 · #**124** 03-06-2010, 11:48 PM

Oh boy... I let the radio heat up for 15 minutes or so, I tuned into the only station that I could hear. Starting with C-27 on the 2nd IF I tweaked just slightly one way then another and got a little clearer reception. The went to C-24 on the same and got a slight edge there as well. Then I went to C-19 and it got quite a bit better. Then came C17 and the moment I touched the screw I heard "clap" and no more sound.. dead... empty. The tubes look OK physically, there seem to be the same voltages as before, though I didn't check them all yet. There doesn't seem to be any excessive heat and no smell. What to do???

Oh, and I was so looking forward to President Roosevelt's speech tonight.

de.facto7 · #**125** 03-07-2010, 12:43 AM

Somehow, my radio is back and now I have 2 stations. Go figure. I noticed when I touch the top of the 6K7 the sound stops. When I touch the top of the 6J7 there is a high pitched squeal. That isn't why it stopped working before I don't think but it's an observation.

Reece · #**126** 03-07-2010, 08:15 AM

Sometimes the IF transformer adjustment screws can be "hot" and can short B+ to the can, so it's good to use a plastic alignment tool for that, RS used to sell them, still might? In lieu of that, you can wrap a piece of tape or use heat shrink tubing around a small screwdriver shaft just leaving the very tip exposed.

Did you clean the tuning capacitor? Be careful not to get this on the trimmer caps with their mica insulators on the side of the tuning capacitor, as the mica can be damaged. Blast in between the tuning plates with computer keyboard cleaning "air" or with CRC Electronic Cleaner, available at auto parts stores, leaves no residue. Inspect, be sure none of the rotor plates are touching the stator plates. Clean out the ball bearings with a solvent and regrease with a little light grease like white lithium. One drop of light oil from a toothpick on the other cap bearings.

Check to see if your local oscillator is working. Place another functioning AM radio tuned to an unused frequency about 1500 Khz right next to your GE. Turn the GE on and tune it around between 900 to 1200. At some point there should be a squeal or a "rush" from the other radio indicating your GE's local oscillator is working. This signal will come in at the GE dial setting plus the 465 Khz I.F. frequency, so 1000 on the GE should come in at 1465 on the other radio.

de.facto7 · #**127** 03-07-2010, 11:12 AM

Great info... Thanks for the tips... back to radio land. Someone at the electronics store said he used denatured alcohol to clean the tuning cap then compressed air. I have stayed away from it so far just to be careful.

Martin

de.facto7 · #**128** 03-07-2010, 12:32 PM

I get a squeal with the GE at 1060 khz and the other radio at about 1500.

Reece · #**129** 03-07-2010, 12:54 PM

That's great! It means your local oscillator is working so that it can mix with the received signal to produce the I.F. frequency. I wasn't sure before if you were just receiving an RF signal blasting through or if the superhetrodyne circuits were working.

What I like to do is make a copy of the schematic and then go over the chassis wire by wire and mark them off one by one on the schematic with a highlighter as I go. Concentrate now on the circuits around the 6A8 and the 6K7. Something keeping the signal from getting strongly through the IF section? You mention a 50K resistor inside an IF can: I don't see it; can you I.D. it on the schematic? Does it look factory? Sometimes resistors are used to lessen selectivity but ...?

Do the easy stuff first! Clean the cap!

de.facto7 · #**130** 03-07-2010, 01:55 PM

It looks like all the other dogbone type that were underneath. I don't see it on the schematic. It's green w/ a black end and an orange dot... I guess 1/4 W. It looks factory. When I tap the top of the 6K7 once, there in a quick squeal then the reception gets way better for a minute or so. The volume increases by 2 x and the hum is less noticeable. Does that conjure up any possibilities?

Reece · #**131** 03-07-2010, 02:54 PM

Did you clean the tube pins and sockets? This sounds like intermittent connections. If you have some electronic cleaner, put some in a bottle cap and use a cotton swab to put some on the pins of one tube, then plug the tube in and out of its socket several times. If no cleaner, use WD-40. Do all the tubes, including the top caps. See if that helps.

de.facto7 · #**132** 03-07-2010, 04:06 PM

The tube pins are clean. Cleaning the sockets is a conundrum. I lost 2 sockets so far probably because of naval jelly seepage causing an arc between the wafers. Personally, I think WD-40 could very possibly do the same thing. I have deoxit but the same applies. Denatured alcohol is the only thing I can think of that would have absolutely no residual effects. Even compressed air can leave a water residue if it gets in a closed space and doesn't dissipate fast enough. This is my experience with mother boards and computer components.

If I could just get something small enough that I could put a thin cotton cloth over like a handkerchief, dip it in the alcohol and put it through, It would seem to me safest. Hey, don't listen to me. I'm a rookie.

I did all the cleaning you suggested earlier. Thanks.

Reece · #**133** 03-07-2010, 05:58 PM

Plugging the wetted tube pins in and out of the sockets won't wet the sockets. The pins will get a little of the cleaner juice on the socket contacts and improve things. I've never had any problem this way. Any socket problem from before is probably from the naval jelly, which is corrosive stuff. If you're antsy about it, just wiggle the tubes and the ones that give a crackle, plug the dry tubes in and out several times. Look underneath and see if the pins make good contact with the socket terminals. Always a possibility on 74 year old stuff! Anything iffy you can always bend a little bit.

Reece · #**134** 03-07-2010, 06:24 PM

In the underchassis picture: the square brown cap with six dots on it: can't tell from the picture. What is the mfrs. name on the cap? When reading the mfr's name on the cap right side up, which dot is in the upper left hand corner? What two points in the circuit does the cap connect to? Have you identified it on the schematic as cap no. XX ?

de.facto7 · #**135** 03-07-2010, 07:08 PM

It's a Cornell-Dubilier. The name reads twice in both directions so the name is always up. If you read the usa written to the left in the upright position, the upper left dot is blue. There are several of those type under there. I haven't replaced them.