GE A-66 new refurbish job - Page 6 - Videokarma.org TV - Video

sean · #76 03-04-2010, 01:28 PM

Do you mean C14? The negative will go to the chassis. The positive connects to pin 8 of the 5Z4 (5Y3) according to the wiring layout. The negative leads of all of the electrolytic capacitors in this set are connected to the chassis (C13, C14, C31, C32, C33, C36, C37).

de.facto7 · #77 03-04-2010, 02:59 PM

You will have to fill me in here. The original wiring (and what I can decipher on this rather illegible schematic) goes from 5y3 pin 8 to the 10uF 500V to the speaker. Now, all the caps on the other side of the radio are connected directly to ground. The multi dry cap packs (replaced with ECs) go to ground. The 16uF goes all over the place with a lot of smaller caps a VR... I usually get replacement right, but I'll have to say I could have been asleep or something.

Comment away!

de.facto7 · #78 03-04-2010, 03:43 PM

OMG... Are those 2 caps, 10uF and 16uF, grounded by their old mounting? If so... There is a problem! They are not on their mounting anymore. They are just clipped off and the new caps are underneath... wired incorrectly!

bandersen · #79 03-04-2010, 03:49 PM

Quote:

Originally Posted by de.facto7

OMG... Are those 2 caps, 10uF and 16uF, grounded by their old mounting? If so... There is a problem! They are not on their mounting anymore. They are just clipped off and the new caps are underneath... wired incorrectly!

Yes, most likely they were. How did you wire the new caps ? Like sean said, the negative goes to the chassis.

de.facto7 · #80 03-04-2010, 04:39 PM

Got it! I just rewired. It seems a lot more logical that's for sure. I looked closer at the old cap mounting and saw a rubber insulator separating the center of the cap from the screw in mounting and got the message. A little late but at least I know how those things work now... and don't work as well. I don't see all that well and thought the 2 solder points on the base were separate pins, so I just tried to figure which was was + and which was -. That was stupid. Everything was split and going nowhere!

I am going to take a break before I look things over and fire it up again.

de.facto7 · #81 03-04-2010, 06:47 PM

Well, that was interesting but no cupie doll. I have 4V on pin 2 to ground now on the 5y3 w/o tube and 6f6 with tube. With both those tubes in and the speaker plugged in, I still show a short on the bulb tester but not as sharp as before; it's still too high though. Without tubes, all the main voltages have reasonable readings as before. I still show no voltage on the + side of the 10uF 500V cap (which in now neg. to chassis).

Heeelllp! I'm not sure what to check next.

If my schematic was clearer, I think it would help. Are there other sources for those manuals? This is just such low res that even panning in, the words and numbers are a complete blur. Since I don't know enough about electronics, it's all guessing for me trying to figure it out.

You guys have been great and very patient. Thanks.

sean · #82 03-04-2010, 08:23 PM

I scanned the Rider information that should be better than what is on Nostalgia Air. Shoot me an email and I'll email it to you. seanbart at fidnet dot com.

You probably didn't do it but you want to make sure that the old electrolytic can capacitors are not connected to the circuit. Don't use the original positive connection on the can as a tie point to connect the positive of the new capacitor. Leaving the negative side of the old cap connected is fine just as long as the positive is not connected also.

de.facto7 · #83 03-04-2010, 09:17 PM

Yup. The old caps are fully dysfunctional! They still look nice on top though. And thanks for the offer!

leadlike · #84 03-04-2010, 10:01 PM

Without the 5y3 tube in place, measuring from either pins 2 or 8 to ground will give you a skewed result. Put the meter lead on BOTH pins 2 and 8 to measure ac voltage across them. It should be 5v-8v. Now, with the 5y3 pulled, also measure from pin 4 to ground and pin 6 to ground. You should be getting some pretty high ac voltages (250v, 350v) there as well.

de.facto7 · #85 03-04-2010, 10:11 PM

Yup... I wasn't thinking. I get 370VAC 4 and 6 to chassis tubes in except 5y3, and 395VAC all tubes out. I get 5.5VAC between pins 2 and 8 when all but the 5y3 are in and 7.4VAC when all tubes are missing.

de.facto7 · #86 03-04-2010, 10:16 PM

How does one check the speaker transformer? I get an arbitrary 1.281 ohms on 2 of the speaker connections... probably a 1 ohm speaker. I'd better not put it on my stereo lest I blow out my output transistors.

leadlike · #87 03-04-2010, 11:36 PM

For speaker transformer, do you mean the field coil, or the audio output transformer? The speaker itself should have 3 or four connections (it depends on if the field and voice coils share a ground connection). The field coil should have about 1330 ohms across it, according to the schematic, while the voice coil of the speaker should be something like 5-6 ohms (it has a hum-reducing coil in series with it).

These old speakers use the field coil as an electromagnet, as well as a filter in the power supply for the whole radio. Hence, if the speaker is disconnected, it will kill the power to the whole radio.

If a field coil speaker is dead, fret not, modern speakers can be used. Simply hooking up a modern 8 ohm speaker to the radio's old voice coil connections will get you started, and to make up for the missing field coil, put a fat 10w resistor of 1300 ohms value or so across those old field coil leads to replace it. This isn't to say that your speaker is necessarily bad; but I figured I would cover the wonderful world of electrodynamic speakers while we were on the subject.

....Although now looking at your readings, it looks like your rectifier tube may be working, and the next thing down the line that would kill your radio's B+ would be your speaker-isn't this fun?

de.facto7 · #88 03-05-2010, 01:00 AM

For me... it's as fun as it gets. Many call me boring though.

I'm going to come back to your speaker discussion in a moment but I have been doing some snooping. I have tried to follow as many circuit connections as possible and following the schematic as much as I can decipher it. I started backward from the speaker connection (3 of them to the radio) following the path through the caps, power, switch eventually terminating my adventure at the 6f6 and the 5y3. everything was connected correctly, polarity on caps correct, I even checked all the solder joints and did a continuity check on all the connections therewith. I can't see anything wrong. So, I plugged it all back together and raised my light bulb to 75W. As it should, the bulb went up while things charged and then backed down again though not as much as I would expect. The tubes started to glow and after about 30 or so seconds, I heard a little noise in the speaker. Not much. Well, WTH... I put in a 150W bulb and the same thing but the tubes were brighter. The bulb started up slow and stayed there then went up to about 20% at which point I heard more noise in the speaker. Not a loud hum or a lot of static or Inagodadavida or anything, just that radio noise when there is no station and your between bands of something. So, I said... let's burn the house down! I plugged into the house current.... and the house didn't burn down.. neither did the radio. It just warmed up for a few seconds, the tubes were nice and bright and the speaker was the same as before. 'no noticeable electrical odor, no exploding caps. Upon adjusting the tuner, I got nothing, but then I don't have an antenna wire hooked up either. I figure, when it's time to think about tuning I'll think about an antenna.

OK... what have I got guys?

Speakers... There are 3 wires from the radio to 3 of 5 pins at the plug. The plug on the speaker side interestingly is connected directly to the voice coil! Hmm, never saw that before. There is a transformer of sorts that is screwed right to the back side of the speaker frame. That's the one I was talking about. The main speaker coil is not in question.. yet. BTW, I just built a set of 8 Ohm speakers for my stereo amp with homemade 2 way crossovers made on a PCB that I drew then etched with peroxide and toilet bowl cleaner. They are working really well.

But, I still don't know much about antique radio, that's for sure!

bandersen · #89 03-05-2010, 02:05 AM

Does it look something like this ? This one has two wires going to the field coil and two to the audio output transformer bolted to the back.

Looks like yours has a common connection between one end of the field coil and the audio output transformer so only 3 wires are needed.

de.facto7 · #90 03-05-2010, 02:38 AM

It looks similar but comparing the plug size to the overall size, it looks as if mine is much larger. Mine is about 10" across. Mine also has an actual transformer bolted to it on the side like where those sets of 2 holes are in your picture and completely separate from the magnet coil in the middle. The male plug has 5 pins and an extra space. The female side has 5 holes but only 3 have actual contacts in them that are wired back to the radio.