GE A-66 new refurbish job

[de.facto7]

Reese... (and everyone else for that matter) the radio sockets and tube pins are pretty clean and the connectors tight. The squeal I am talking about has to do with just coming in contact with the top of the 6K7. It's not the tap itself. I said tap to illustrate the amount of time I am in contact with it. If I put my finger on it and hold it there the squeal is painfully loud. It's a really high pitched squeak, squeal, electrical... yikes, it's loud. But everything is improved after I do that. When the machine gets really warm, it "seems" to hold more stable. It's hard to tell. I am actually beginning to hear transmissions on the SW bands. I can't make anything out but their are voices.

This is pretty fun.

[Reece]

Where are the two wires from this cap connected in the circuit?

[de.facto7]

It goes from ground to the OCS at what looks like L8. It's one of the terminals of the oscillator. Looks like C11.

[de.facto7]

I have been giving the wrong information about the squeal sound...

I have been repeating 6K7....

It's the 6J7 that makes the noise and increases the reception... the amp tube

Sorry...

[Reece]

Wonder if one of the tubes is oscillating, or if RF is getting into the 6K7. Then when you upset the apple cart by touching the top cap it stops for a while. Did you replace the IF cans to operate the radio? They're needed for shielding. That 50K resistor inside the IF can could be reading off due to being in circuit? Might lift one end and check. I might try bridging small micas in the detector/1st audio area with another small mica, see if there's an improvement.

Some other ideas out there?

[de.facto7]

Great... I'll give these a try! I just read yesterday that this fading out can be a bad cap or a weak tube. All caps except the micas have been replaced. What do you think? Yes, the cans are in place.

[de.facto7]

Here's another little tidbit. There is supposed to be a 1M ohm resistor from ground to the intersection of the wire to 6J7 and another to a cap that leads to the volume control. With the resistor in place there is no reaction from the 6J7 and no hum but the sound volume is almost nonexistent with the volume turned full blast. I have tried lower resistance 500K, 220K, 100K, 50K, 20K... the sound gets more distant till it totally disappears. If I remove resistance completely, the hum resumes but I have all the volume I can handle.

Can someone tell me what's happening here?

Thanks!!!

[de.facto7]

I followed the suggestion that Tubology so graciously offered about following the circuit and checking off as I go. Well, there ya go... I found one more stupid mistake. A .05 cap had been in the wrong place.. Voila, I have a lot more reception, less hum and less of that weird tap thing on the 6J7. It is still there but about 5 x less. Although, I still have to go without the 1M ohm resistor I mentioned last post or there is very little volume.

I'll keep going and see what I come up with. SW is a bit weak, but it's nice to have AM!

[Reece]

Tracking down that hum: is the resistance element in the volume control OK? With the set turned off: see the three terminals that are together: clip your ohmmeter to the two outer ones. Should get around 250K. Then clip to center and one outer, by turning the control shaft should be able to vary from 250K to practically zero. Center and other outer, should vary the same but in reverse.

Is the low side terminal of the volume control solidly grounded? This would be the outer terminal of the three terminals together, that is the lower one on the schematic shown going to ground.

As to the rogue 1 meg resistor: try higher values and see what happens. And keep tracing that schematic when you're rested!

[de.facto7]

Now that's the strangest thing... on the volume control, outside on either side to the middle, the resistance goes from 0 ohms to about 260K ohms... at half way! continuing, it starts down again and at full volume ends at 100K ohms. From side to side I only get 88K. But the volume does work...

Oh.......... scrap all that. This is an edit.

I just removed the volume control completely to get a better reading. It's 0 to 254K ohms on one side, then 0 to 355K ohms at 3/4 way then goes back down to 254K.

Side to side it's 254K.

[de.facto7]

I'm almost there, Guys. I just found an old antique collector in town with
some old tubes. One of them was a 6J7 G so I though why not. I gave him a dollar and took it to a place with a tester. It tested as high as it can get. I stuck it in and the hum is down to practically nil. The volume is not quite as high but at least there's no hum on stations and practically none in between. Most of the reception issues now are just antenna related.

I would like to send out a huge thank you to all those who have guided me through this adventurous procedure. I have a lot of computer and mother board experience... but in computers, all the real important stuff is already laid out and you just have to know your passives and hardware. Working on this antique radio has sure showed me how much I don't know about what is at work in electronics. I would bet that more than 75% of computer "experts" are just "package" experts, E.G. tear open the plastic bag, stick the part in the little holes in the traces and solder it in. Even when you are working with PCB, you lay it all out before hand and the traces are perfect (hopefully), then you don't think about that anymore and stick in the parts. Big deal. But with radio.... the wires, the connections, the modifications, the common sense, the rudimentary circuitry, 3 dimensional space instead of 2... It makes one think in a whole different way, a more thorough way.

I think the only thing left to do is to try adjusting the SW side. Is there a general procedure that can get me pretty close. I don't have a scope or anything but reading the manual there are tools mentioned that I'm not sure I understand how to use or make like the metal filing thing or the ring. It would be really interesting to try to tune this up the old way, the way it was done back in the 30's.

Guidance offered would be greatly appreciated!

Thanks again,

Martin

[leadlike]

That sounds wonderful! I wouldn't mess too much with the shortwave (or really any of the other radio settings) until you find a signal generator. If you are receiving any SW stations, you'll find your radio can be extremely fussy about tuning them in-so if you find yourself just wiggling the tuner back and forth with just the smallest of movements, well, that's how it is for all of these sets (and that is why we have a fine tuning knob on nicer sets).

You should be able to pick up any old signal generator for next to nothing. Even the most basic ones will have the features you need. Maybe even a member here might have one they would give away. I only just threw away two working ones this past January.

[Reece]

EDIT: I was working on this post for a while and when I posted it I see Leadlike had posted: he's right about using a signal generator to get it right, but if you want, and are careful, you can get good results by ear.

****

Hooray! You basically tracked it down yourself. Your radio shouldn't need heavy alignment since it works pretty well now. I am going to bet that you won't need to turn any screw but just a few degrees in either direction: resist that, please. You can do it the way old timers did/do it, without any test equipment, and have it pretty close to perfection with a screwdriver.... You should really use a plastic screwdriver alignment tool but will be OK if you insulate the tip of a small screwdriver.

Have your ten to twenty feet or so of antenna connected. Warm up set for 20 minutes or so. Be sure the dial pointer is correct in its travel per page 6 of the NostalgiaAir (N/A)instructions for the A-64.

Always use weak stations for alignment. This avoids having the automatic volume control (AVC) acting which can confuse hearing when the signal peaks. Set your volume for a normal listening level.

High end of broadcast band: Tune to a weak station around 1500 to 1600. You must know the actual frequency of that station. You may have to listen for it to be announced if you don't know it.

Look at N/A Fig. 4 to identify locations of adjustments. If the dial pointer is not on the exact stated frequency of the station you are hearing, carefully adjust the broadcast oscillator screw just a little left or right to shift the station on the dial, following it either up or down the dial as required with the main tuning knob. Then adjust the broadcast R.F. coil trimmer for max output.

Low end of broadcast band: Tune in a weak station around 550 to 650. "Rock" the tuning dial back and forth across this station while slightly adjusting the padding capacitor next to the oscillator coil for loudest signal. The dial pointer may not line up exactly with the stated frequency of the station at the low end of the dial but that's the nature of the beast.

Intermediate Frequency : Tune in a weak signal around 1500. Locate the I.F. transformer adjustments per Fig. 4. Peak for loudest signal in this order:
Second I.F. Secondary
Second I.F. Primary
First I.F. Secondary
First I.F. Primary
Then repeat in same order.

Short wave: The National Bureau of Standards has a time signal station that broadcasts exactly on 10 and 15 megacycles (or megahertz), among other frequencies. If you are not familiar with what this sounds like, listen to this demo: it's like a clock ticking over a continuous tone, interrupted by time announcements. Open and click on "Hear Signal."

http://tf.nist.gov/stations/wwv.html

Tune the radio around 15 Mc. to see if you can hear this signal. It will be stronger during the day. You might need to add a longer antenna. The station is also on 10 Mc. but is stronger there during evening hours. It would be better to align at the 15 Mc. signal if you can. Check to see if the pointer corresponds fairly closely to the dial number. You can "walk" the dial pointer up or down by adjusting the SW oscillator trimmer. SW fades in and out a lot so don't let that fool you when peaking the trimmer. Then adjust the SW R.F. coil trimmer for max output.

Oughta do it!

EDIT: Looking at the N/A entry again, I see that G.E. calls what is usually called the "antenna coil" the "R.F. Coil" (Radio Frequency.) Accordingly, I changed the references above to R.F. Coil.

[de.facto7]

You guys are great. Thanks for the info!

a couple of tweak questions:

When turning the First I.F. Secondary,I think that's L-19, I noticed it is turned as far clockwise as it can go. I can't find the center point since counterclockwise is only to lessen the reception. All the other I.F. adjustments have a clear center point. Could there be a weak component that keeps it from setting farther clockwise?

To clarify, I'm not convinced it's the volume pot necessarily.

The other is, Could the not quite right volume potentiometer cause the sound to be gruff? It works OK but the sound is gravelly especially when turned higher than 1/3.

Thank you.

[Reece]

Sounds like something has drifted in the first I.F. Easiest would be to parallel a small mica cap, maybe 10 to 20 pf? across that trimmer C19. Just tack one in to test. This would increase the total capacity. Since the capacity would now be too much, it should allow you to back the screw off to lower the capacity to find the peak.

Rough sound: is the speaker voice coil rubbing on the pole piece? Sometimes this is only apparent with higher volume. With the set off, with fingers of both hands carefully move the cone back and forth to check for rubbing. Jump a PM (permanent magnet) speaker across the voice coil terminals of the original speaker to see if there's a difference in sound.

Do you still have excess hum? You could set the speaker over a hole cut in a cardboard box for a baffle to hear the hum better. If there is hum, does it follow the volume control setting? If the control works smoothly with no jumps, don't think the control is the problem.