GE A-66 new refurbish job
 

Greetings!

I just opened this up today and it's certainly new ground for me. The oldest thing I have redone is a '72 Sansui stereo amp receiver. This is really amazing. It's Oooold! Any input would be greatly appreciated. Some things that come to mind are what not to use for chemicals if any. I'm not sure if it's OK to use Deoxit or denatured alcohol even. Some of these parts look more like Halloween candy. (BTW, notice my snack in the upper right hand corner of the first pic.) Should I replace the caps with modern electrolytes or go to polyprope or???? Other parts I have never seen before; I have no idea what they are. But I'll go a step at a time.

Any help? 'Looks like fun to me.

I don't see any of your pictures :headscrat

Oooops

Ah, much better :D

Cool radio - early 30s I believe. Looks to be in rally good condition.
Just about all of the cylindrical parts you see below are capacitors. A few are resistors like the big yellow bugger with an orange spot on the right - AKA a "dogbone".
I'd use polys for all the caps below including the two metal box caps.
Modern electros for the two big caps on top.

Thanks much for the information. Underneath, what is that brown square object with the multi colored dots on it?

Glad to help. That's a molded mica capacitor. They rarely go bad so I'd leave it alone. Check out these links for the color code:
http://www.vcomp.co.uk/components/ca.../cap_codes.htm
http://www.radioremembered.org/capcode.htm

Fantastic!

.. a couple very general but necessary questions before I start this project...

Are there any abnormally toxic materials that could be found in parts of this period?

Are there any bad combinations of chemicals that I should avoid either that could be hazardous or could cause damage to these wonderful ancient artifacts?

and.. is there anything that is delicate that I should just leave completely alone?

Thanks again...

The yellow colour of the chassis comes from cadmium plating. It is quite poisonous, so wash your hands after handling the chassis. Other than that, the solder is partly lead. This accounts for most of the toxic materials.

Whew, good to know. I noticed that part of this chassis has a greening look to it. Mold? Copper? Arsenic???

That's probably cadmium oxide too. I've been running into it a lot lately. I posted a thread about how to remove that oxide and polish it up. As amptramp said, it's toxic so beware!

If you're wondering why they used it - it's prevents rust, is easy to solder to and looks nice. At least at first.

http://www.videokarma.org/showthread...=246991&page=2

There is one of those languishing in a warehouse here in Lancaster. It's a big junk shop and they have about a half dozen old consoles rotting away there. While they are way overpriced, I did buy my first tube powered radio there (an RCA) the GE was my second choice, as I liked the drum-shaped tuner. For a first restoration, this should be an easy one-not a lot to replace, and a very open, easy to work with chassis design.

That's great news. It looks like a really interesting fix-up.

I am making a parts list for replacement and there are 2 silver paper board boxes on the underside that have familiar markings but unfamiliar presentation:

One says - 4mF 450V GEP-5, 3mF 150V DGP-2
The other says - 450-25V 4-10mF, SGP-2 CCCW

They sound like caps but what does it mean when boxed like this? I can't see what's inside and one is riveted to the chassis.. and the GEP, DGP, SGP are unfamiliar. My guess is the CCCW is 300 watts??

help?

Each of these boxes contain two capacitors. The first one has a 4uF at 450V and a 3uF at 150V. The second box has a 4uF at 450V and a 10uF at 25V. I am not familiar with the GEP-5, DGP-2, SGP-2, or CCCW. I would guess they are manufacturer part numbers.

If you haven't found a schematic for this set you might try this one:
http://www.nostalgiaair.org/PagesByM...4/M0007754.pdf
Nostalgia Air does not have a listing for the A-66 (other than 1 page in the Changes section of Riders). I am assuming the 6-14 on one of the silver boxes was put there by someone who had worked on this set previously. It corresponds to a Riders manual page for the A-64 and A-67 models.

Those mid 1930s GE sets are very good performers and are very well built. They are under appreciated by collectors.

Thanks for the map! I had no idea things like that were still around.

I promise to stop bothering you guys as soon as I can get my chicks in order but I was wondering, where does one find some of these caps? E.G. 16uF and 8uF @ 500V and some of those other high voltage things? I can only find 450 to 475 in those 8 and 16uF caps. The others I can basically find but it's a mishmash polyprope, polystr, metal film and small electrolytic. Some have to have much higher voltage ratings to fit the uFs. I looked at Mouser and DigiKey.

The other thing are those dogbones. I have a pretty good idea how they read but not in any really solid way, just an old chart that's from the 40's. Is there a solid chart or explanation that can be relied upon with no discrepancies with the Philco versions?

I've never fished these waters before...

Thanks

I believe all the old dog-bone resistors use the "BED" body,end,dot code...
More charts here:

http://www.vintageradio.me.uk/info/Componentinfo1.htm

Have fun!
jr

Why, son, that set ain't old. :D It even uses octal tubes, so it's from about 1936 or so. Many consider that era of '36 to '38 the peak of radio perfection.

Age of radio perfection.... If that's so, what can I use instead of a screwdriver?:D:D

Perfection may be hard to reach but pretty darn good is attainable. Dig right in!

I have this flexible resistor that I can't read on the schematic and I'm not sure how to read the code on it. My meter shows fluctuating readings sometimes 1.2Kohms sometimes 3.4K. It's one of those that looks like a cable with wire winding on the ends. It's brown with 2 painted stripes, green and gray. The gray one is a guess. It could be brown or silver but I have to bet on gray. No color on either end. The schematic is illegible on that particular item and the parts list shows 3 flexibles. I can only find this one on the radio. In the process of elimination, the radical meter readings just don't come close.

If someone could give me an idea how to read this thing, it would be greatly appreciated!

Thanks

You can get 500v caps at justradios A 10uF should do fine for the 8uF cap.

I would assume that flexible resistors use the same color code as carbon resistors. The only one in the parts list that could match based upon the green stripe is R19 which is 450 ohms. I would think it would have yellow-green-brown stripes. Looking at where it is connected in the circuit would be a better way to determine which one it is. R19 is the cathode resistor for the 6F6 so would connect between pin 8 of the 6F6 and ground. R2 is the cathode resistor for the 6A8 and connects between pin 8 and pin 1 (ground) of the 6A8. R5 is the cathode resistor for the 6K7 and connects between pin 5 (5 is tied to 8) and ground.

Thanks Sean. That helps a lot.

I have another question. I'm a little dumbfounded about these dry cap packs with multiple ratings and voltage. How do you replace those? I've never seen this kind of thing before nor do I know what to use in their place. Is there a way to wire in 2 separate caps for each one? Honestly, I don't even know how they work like that.

I would really like to learn about this and take a stab at it.

Thanks!!

I'm working on a few of those right now too. Check out my thread - I put up a bunch of pictures: http://www.videokarma.org/showthread...=246672&page=5

You could just clip the wires going the old ones and solder new ones in.

If you want to try restuffing them, the first step is to unsolder the pack and remove it from the chassis. Then, you need to figure out how to get the old guts out.

The last few I've done had metal tabs I could bend back. A little heat loosen up the tar inside and the old caps slid out. Next, I used some lacquer thinner to clean out any remaining gunk. I soldered new polypropylene caps in place.

Finally, for a couple of them, I refilled them with commercial grade wax. A little foam stuffing or hot glue would work too. Just so the new ones don't flop around inside the box. Bend the tabs back over to reseal the box. Remount it and solder the wires to it.

The worst part is definitely all the tar :yuck:

Good luck
Bob

Thanks Bandersen. The ones I am talking about are in rectagonal silver cardboard boxes one of which is rivited to the chasis. One of them says, for instance, 4mF 450V GEP-5, 3mF 150V DGP-2 on the box which are 2 different caps. Upon opening, there is one large cylindrical clump of wax and tar that is wired green and red on one end and black connected to foil on the other.

Hmm

That makes sense. The black should be a common ground connection. The red and green will be the other end of the 4mF and 3mF capacitors. You'll need to consult the schematic and trace the wiring to determine which is which.

You can clip out that old lump of wax and tar and solder your new caps in there.

If you want to use poly caps, Mouser has some.

3mF @ 200v

4.7mF @ 600v


Alternately, you could use a couple electrolytics.

Thank you so much... You know, I think I have it all figured out now (hope) and when the parts arrive it will be a go! I'll start working on the chassis with the Naval Jelly and get'er all cleaned up for the re-cap.

I'll be back with progress!

Hey guys... I'm back.

I have a problem. I've been pretty lucky in the past with computers and stereo rebuilding considering I am highly inexperienced in electronics. I've recapped many a mother board with success etc, but this!... this advanced tube technology... it's over my head I'm afraid. I am very willing and ready to learn though.

The A-66 is completely recapped. I replaced most of the resistors. I replaced all the wiring that was necessary which was 95% of it. I have stayed away from the coils except to replace absolutely necessary main wires so as to do as little disturbance to them as possible; I only replaced those wires by continuing from the old wiring about an inch off the coil's solder points. I have done the best I can to replicate the capacitors and resistors according to the specifications of the removed part.

With all tubes removed, I plugged into my PMV w/ a 60W bulb. It shows a short; there's no drop in the bulb brightness. Both power plug leads show no continuity with the chassis. With power on, I get 3.4V AC on the chassis.

Like I said before, I've been pretty lucky in the past but I guess here's my chance to learn some troubleshooting electronics. If anyone is willing to help, I would surely appreciate it.

Thanks! :ntwrthy:

I would suggest checking resistances of the windings in the power transformer with the power removed. Make sure they are close to what is shown on the schematic. Also measure resistance from the lead of one winding to one lead of each of the other windings to make sure there are no shorts between windings.

I'm not familiar with the term "PMV" but I would assume that this is what is commonly referred to as a "dim bulb tester"?

PMV = Poor Man's Variac

Yes

Thanks for the tip Sean. I made 2 preliminary readings but I also need to ask if I'm checking it correctly. I followed 2 of the wires that the schematic says are on a particular coil and did the same with another. Both lead to the power rectifier plug. That is where I took the readings. I don't know if that is the correct way to get that or not. On the schematic, one is supposed to be 200 Ohms and reads 380. The other is supposed to be .2 Ohms and reads .6 . I haven't dug around for the other 2 before I find out if I am doing this right.

If this is correct, then the transformer is shot I guess.

Any input? Thanks!

one other thing... there doesn't seem to be any short between those 2 coils using the same system I just explained.

and yet another update... Measuring from one end of the 200 Ohm coil to the chassis, I get 198 Ohms and on the other side of that coil wire I get 187. On the wire going to the .2 Ohm coil to the chassis I got .2 to .3 Ohms then I double checked it a minute later and I get no reading at all and haven't since. Hmmm :scratch2:

Have you disconnected the transformer secondary leads from the radio ? If they are still wired into the set when you take your measurements, you could be getting bad readings due to wiring or component problems down the line.

Nope! I had better do that. Thanks. 'taking one step at a time...

If you turn on the power switch and measure between the pins of the power plug you should get around 6.4 ohms. You should get an open circuit between either pin of the power plug and the chassis.

Between pin 4 of the 5Z4 socket and the chassis you should get about 200 ohms. Between pin 6 of the 5Z4 socket and chassis you should also get about 200 ohms. This seems to jive with what you mention in your last post.

Between pins 2 and 8 of the 5Z4 socket you should get 0.2 ohms. You should get an open circuit between either pin and the chassis.

Between pins 2 and 7 of the 6F6 you should get 0.2 ohms. Between one of these pins and the chassis you should have a dead short. Be sure to remove the dial light before taking measurements for this winding.

If you disconnect the center tap of the B+ secondary (winding connecting to pins 4 and 6 of the 5Z4) that should isolate all the windings from one another and you should not get any continuity between any of the windings.

On your PMV you do have the light bulb wired in series with the radio and not in parallel, right?

That's detail. I'll get to it.

Yup, the PMV is in series. I have used it many times for other projects. 'Works great.

Thanks

OK...

Your first and second paragraph tests out OK.

If I am counting the pins correctly on the 5Z4 (the schematic is illegible and marked with letters P1 P2 H S can't read the others) then I am getting between .5 and .6 ohms between pins 2 and 8.

On the 6F6, I get between .3 and .4 ohms between 2 and 7 (again if I am getting the pins right). Both pins are grounded to chassis as a matter of fact only pin #5 and #6 are not grounding to the chassis.

The dial light is clipped and pin #6 is disconnected on 5Z4

On the matter of the 6f6, here is a tube diagram of that little feller:

http://www.nostalgiaair.org/tubes/6f6.htm

pins 2 and 7 being the filament, you will pretty much have your multimeter reading as a short to ground for both of those pins while the tube is installed, as the filament is of very low resistance. If both pins 2 and 7 still read as a short to ground when the 6f6 tube is pulled, then you could have a problem.

On the issue of all of the other pins, save for 5 and 6 being grounded; pin 6 isn't used on this tube, though there may still be things soldered to it, being used as a tie point for other parts in the circuit. Pin 5 is the signal input grid, so that makes sense that it wouldn't be grounded. Looking at the schematic, it appears that pins 3,4, and 8 should not be grounded. But we'll mess around with that issue a bit more once your transformer issues are cleared up.

Guys.. Thanks for the help. I learned how to track down a circuit without a PC board. I was able to use the detail as well as the bits and pieces of info about tubes and the pin setup and I found 2 wiring mistakes, my mistakes of course, that put my PMV (dim bulb tester) to sleep!

The 60W dropped right back but it didn't start out very high as I am used to for getting those caps jump started. Then after about 2 seconds, I started to hear something very faint and my gut reaction was to flip the switch on the PMV which I did. It wasn't like a crackle or a fizz but more like a faint hiss. Anyway, there was no smell or smoke or heat that I could tell. I still have no tubs in, but that pin 2 and 7 on the 6F6 are still showing ground to chassis. After figuring out which pin is which... 3, 4, 6 and 8 are not grounded... 1, 2, 5 and 7 are. 6 isn't used.

Should I turn the thing back on? I'll wait for now.

Do you see a physical connection between pin 2 and the chassis and between pin 7 and the chassis on the 6F6 socket? If you are saying they are both grounded because of the resistance readings then you are measuring through the filament winding of the transformer (or a short circuit in the wiring). Disconnect the wires coming from the transformer from pins 2 and 7 on the 6F6 socket and measure between these two leads from the transformer. This measurement should be low (0.2 ohms according to the schematic). With these leads disconnected measure between pin 2 and pin 7 on the socket. This measurement should be open.

Pin 1 and either pin 2 or pin 7 should be grounded. Pin 5 should not be grounded. There should be about 500k ohms between pin 5 and ground due to the grid resistor.

With no tubes in it you aren't going to get any voltage on the electrolytics. The 5Z4 rectifier would need to be installed to get voltage to them. BTW, as a word of warning for when you get to this point don't ever run the radio with the 5Z4 installed without the speaker connected. Since the speaker has a field coil that is used as a filter in the power supply not having it in the circuit can cause the voltage to get too high on C13 and C14 and they can pop. Been there, done that.