Stuart:
I have a Goodyear "cube" radio model #015070 with the same problem. I even totally re-wired the 6U5 tube socket. and made sure the socket resistor was good. Now I get great green color but the "eye" doesn't move when tuning. I strongly suspect its related to the AVC circuit, since the radio volume does not regulate when tuning between strong and weak stations. I get great volume on both BCB and SW, but I have to constantly turn down the stronger stations and the magic eye does not move. Perhaps someone with more expertise (I'm still a rookie) could offer some advice as how to fix.
Regards,
Allan
:
:Stuart:
:
:I have a Goodyear "cube" radio model #015070 with the same problem. I even totally re-wired the 6U5 tube socket. and made sure the socket resistor was good. Now I get great green color but the "eye" doesn't move when tuning. I strongly suspect its related to the AVC circuit, since the radio volume does not regulate when tuning between strong and weak stations. I get great volume on both BCB and SW, but I have to constantly turn down the stronger stations and the magic eye does not move. Perhaps someone with more expertise (I'm still a rookie) could offer some advice as how to fix.
:
:Regards,
:
:Allan
::
::Stuart:
::
::I have a Goodyear "cube" radio model #015070 with the same problem. I even totally re-wired the 6U5 tube socket. and made sure the socket resistor was good. Now I get great green color but the "eye" doesn't move when tuning. I strongly suspect its related to the AVC circuit, since the radio volume does not regulate when tuning between strong and weak stations. I get great volume on both BCB and SW, but I have to constantly turn down the stronger stations and the magic eye does not move. Perhaps someone with more expertise (I'm still a rookie) could offer some advice as how to fix.
::
::Regards,
::
::Allan
If you will remember that the tuning eye is a vacuum tube Voltmeter measuring the AVC, then you can go back to the AVC bus and check for negative Volts when a strong station is tuned in, the stronger the station, the more negative. Use a high input meter, such as a VTVM or a DMM, a regular analog meter will load down the bus. You will at least know if the AVC is bad or the tuning eye circuit.
Lewis
Well, anyway, regarding eye tubes and AVC, the typical AVC circuit is fed from a high resistance, say, around 2 megohms. The filter capacitor that filters the AVC voltage so that it is smooth (since the AVC voltage originates from the detected audio) is usually around .05 MFD. Any leakage in that capacitor at all is enough to severely load down the 2 megohm resistor. It is generally good practice to replace all capacitors in a radio (save, perhaps, the mica capacitors, since they are highly reliable). However, if you decide not to replace all capacitors, you should at least check them all for leakage....especially in high impedance/resistance circuits. Check capacitors with the X10,000 setting on your ohmmeter. For values larger than .001 MFD, the needle should swing up just a bit and then fall back down to where it started. For values below .001 MFD, needle movement may be impossible to detect. However, for any capacitor, if there is leakage, the needle will swing up from the infinity mark, and it'll stay up. If the needle doesn't fall back to EXACTLY where it started, the capacitor has unacceptable leakage. In circuits where general impedances are below 10,000 ohms, leakage in the millions of ohms may be acceptable. For good performance and reliability, capacitors should have no leakage. For circuits where impedances are in the millions of ohms, it is absolutely necessary that capacitors have no leakage.
....Also, for your AVC circuit, be sure to check the AVC resistor(s) for drifing. Check for shorts to B-. Check all connections and compare to the schematic. Weak signals might not trigger the AVC circuit. You should be able to get at least some movemenet, however, and if you are unsure of where your radio stands performance-wise, be sure that all components check out as they should, and you'll most likely have things working correctly.
T.
Where you could possibly leave a somewhat leaky capacitor would be across a cathode bias resistor or something like that.
T.
:
:Where you could possibly leave a somewhat leaky capacitor would be across a cathode bias resistor or something like that.
:
:T.
I wonder if you could put a DMM in series with a capacitor, and read the leakage current? That's essentially the way we checked the strobe light caps on airplanes. They were 350 uF @ 450 Volts, and ten milliAmperes was the max leakage...in reality they had 2 or 3 mils or off scale, and usually leaky ones had exploded out the pressure relief, giving one a thrilling day of cleaning the electrolyte out of the box.
I also remember a tester that had a neon bulb that glowed for leakage, and would flash for intermittent breakdowns.
Lewis
P. S. watch out, I am going to try my light switch again.
LL
What you can do is either use a diode from Radio Shack connected to the AC mains, or use your tube tester as a power supply. Place a 5K resistor in series with each side of the mains for protection. I think that a long time ago I suggested something like 100K resistors, but that's too high a resistance. 5K resistors should give ample protection against shorts. Filter with a .1 MFD or larger capacitor. Place the capacitor in question in series with the supply and your meter, and take a voltage reading. While I normally replace paper capacitors as a rule (when I have time...otherwise I just replace the leaky ones), I don't usually replace the mica capacitors. As I found in my DeWald television (RCA 630TS chassis), however, units that look like mica aren't always. I had a jittery picture, and it turned out to be an arcing 82 pF cap that feeds the horizontal circuitry from the sync circuitry (or wherever the 82pF cap is...I forgot). Well, the arcing showed up on my VOM as a jittery needle. I put in a new cap and now the picture is stable (still needs a lot of other work, though....by the time I get around to it, they won't be broadcasting anolog signals anymore).
I use my tube tester now. It's an EICO 625. What I do is drop in a rectifier tube of my choice. I throw the cathode down, and the filament to down and center, and adjust for appropriate filament voltage. Then I throw the plate lever between center and up, which leaves it disconnected. All sockets with the same corresponding pin number are connected to the plate as well, so whatever pin number the plate is connected to I connect the capacitor in question to th same pin number in an empty socket. I throw the number 9 or 10 lever up. 9 and 10 are for the grid cap leads. I connect the other end of the capacitor to the 9 or 10 grid cap lead. The SELECTOR switch is set to #4, which is the 200 volt setting. When I press the merit button, any leakage will show up on the meter. If I don't see any leakage, I turn the meter shunt all the way up to 100, which gives maximum meter sensitivity. If there still is no deflection, then the capacitor is most likely not leaky. If you wish, you can also put your VOM in series with the cap. The VOM is more sensitive. For really high impedance circuits it will give you the most accurate reading so that you know that your capacitor is not leaky at all.
....But....unless you really want to save every capacitor in the radio, it's best just to use that test for questionable mica caps, and just replace the paper ones. In my Majestic 180, where the paper caps are enclosed in tin boxes which I don't want to disassemble at this point, I ran tests on the caps, and they passed with flying colors, so I will most likely not replace them at this point. The power supply is homemade by me, so I'm not really worried about blowing out a rare power supply (though the G-80 tubes are somewhat rare). I suppose I could fuse it.
If you wish, you can also use the above as an electrolytic reformer. When I was in need for a 450 volt electrolytic, I grabbed an 8 MFD unit out of a box of old electrolytics I was given. The cap had considerable leakage (like 10K), and would have gotten really hot if used as-is. I let it sit on the tube tester until the meter reading was really low. It now works without overheating in the power supply I built for my Majestic 180. Back when good music was on the radio (two favorite stations of mine changed format last summer), I'd operate the Majestic for 4 to 8 hours at a time with no troubles. Not all electroltyic re-forms work well, but if you're in a jam and you need results now, it's worth a try, I guess. Rule of thumb typically is that if an electrolytic is leaky, it either needs reforming, or it's deteriorating badly (and probably is permanently shorted). If the unit tests as practically open, with no meter deflection, then it's probably dried up, and cannot be reformed.
T.
I'm not sure, I tried to get cute and put my little switch and bulb thingy, but I hadn't had but one cup of coffee, did something wrong...
Lewis
Sir Stuart:
Presently, there is definitely not enough info such that any precise circuit research can be done.
Is this tuning eye unit the stock installation on a Zenith receiver ?….or perhaps you’re trying to make it add on circuitry to a receiver that initially did not have a tuning eye tube ?
Come forth with your specific radio model / chassis and probably more exacting assistance can be forthcoming.
Sir Alan:
I have all the info required on your set, so I have prepared an initial working schematic to consult to, with all of the initial the points of interest marked up…
That being, just in case, that you exhibit the “schematicus readimis problemus” or its equally adverse …”no understanumus” difficulty
Initially, in the viewing of the green route, we see where hi level IF RF signal is stripped from the top of T2 IF transformer via the 100 pf cap and then routed to the detector plate of one half of your 6H6 where the positive nodes are conducted thru the diode and thus leaving you with the negative nodes present on the “yellow brick road” buss .
Down at the R8 //R7 voltage divider the resultant AVC voltage is trimmed down a bit along with an isolative high resistance 2 meg resistor and the 1/2 meg to ground.
What let’s do first is the taking the main AVC #1 voltage with a VTVM….T-VM…..FET-VM or lastly our present day, common digital DVM. We need to monitor AVC #1 for the developed negative voltage while searching for the strongest /or / closest station around…which will coincidentally produce your highest developed AVC voltage.
Tune up for the max on that station and leave it tuned to it. Next move the probe down and monitor for the reduced AVC #2 buss line….for its level and record down for feedback.
Then, just for grins…. of the sets wiring integrity… monitor at the A. B and C test points for the coincidental voltage produced at AVC #2 test point.
And as a last reading, take the voltage on that same reduced voltage AVC buss with the set off of any station at all.
I am assuming that the sole AVC bypass condenser of C4 /.1 ufd is void of ANY leakage or is a new replacement…for a test …lift its ground lead and connect on your + meter probe as is being referencing against your negative lead at ground level. Then see if any of that negative voltage bleeds thru the cap dielectric to your probe.
This is easiest done by grounding that test junction with a jumper wire for a second to chassis and then seeing if any voltage then sneaks through and starts building up.
If the readings look good I will indoctrinate you how to evaluate the tuning eye tube with merely a bit of Scotch tape and 2 toothpicks or a clarinet reed.
Thassit…standing by and waiting for feedback info of experienced voltages:
73's de Edd
::Hmmmm....Lewis....how did you get your text to go outside of the text box???
:
:
:I'm not sure, I tried to get cute and put my little switch and bulb thingy, but I hadn't had but one cup of coffee, did something wrong...
:Lewis
I am definitely afflicted with "schematicus readimis problemus", but am working hard to overcome this disability. I am awed by your overwhelming display of radio circuitry knowledge and am humbled to have the opportunity to be mentored by one of such infinite wisdom!
Many thanks for taking the time to submit the working schematic and providing such detailed information. That's one of the great advantages of this forum, that there are gentlemen like you that freely share your knowledge for the benefit of others (and our collective hobby)and do so with honesty and humor. I will work on your suggestions and check the appropriate voltages this weekend and get back to you with my results. By the way, I have replaced all the caps (the C4 AVC by-pass was a real project being jammed under the variable capacitor).
This is a great old radio and one of my favorite full restoration projects. The tuning eye issue has been the only one I haven't been able to solve. Thanks again for your help!
Regards,
"Sir" Allan
:
:
:
:Sir Stuart:
:
:
:
:Presently, there is definitely not enough info such that any precise circuit research can be done.
:
:Is this tuning eye unit the stock installation on a Zenith receiver ?….or perhaps you’re trying to make it add on circuitry to a receiver that initially did not have a tuning eye tube ?
:
: Come forth with your specific radio model / chassis and probably more exacting assistance can be forthcoming.
:
:
:
:
:Sir Alan:
:
:
:I have all the info required on your set, so I have prepared an initial working schematic to consult to, with all of the initial the points of interest marked up…
:
:That being, just in case, that you exhibit the “schematicus readimis problemus” or its equally adverse …”no understanumus” difficulty
:
:
:Initially, in the viewing of the green route, we see where hi level IF RF signal is stripped from the top of T2 IF transformer via the 100 pf cap and then routed to the detector plate of one half of your 6H6 where the positive nodes are conducted thru the diode and thus leaving you with the negative nodes present on the “yellow brick road” buss .
:
:
:Down at the R8 //R7 voltage divider the resultant AVC voltage is trimmed down a bit along with an isolative high resistance 2 meg resistor and the 1/2 meg to ground.
:
:What let’s do first is the taking the main AVC #1 voltage with a VTVM….T-VM…..FET-VM or lastly our present day, common digital DVM. We need to monitor AVC #1 for the developed negative voltage while searching for the strongest /or / closest station around…which will coincidentally produce your highest developed AVC voltage.
:
:Tune up for the max on that station and leave it tuned to it. Next move the probe down and monitor for the reduced AVC #2 buss line….for its level and record down for feedback.
:
:Then, just for grins…. of the sets wiring integrity… monitor at the A. B and C test points for the coincidental voltage produced at AVC #2 test point.
:
:
:
:And as a last reading, take the voltage on that same reduced voltage AVC buss with the set off of any station at all.
:
:I am assuming that the sole AVC bypass condenser of C4 /.1 ufd is void of ANY leakage or is a new replacement…for a test …lift its ground lead and connect on your + meter probe as is being referencing against your negative lead at ground level. Then see if any of that negative voltage bleeds thru the cap dielectric to your probe.
:This is easiest done by grounding that test junction with a jumper wire for a second to chassis and then seeing if any voltage then sneaks through and starts building up.
:
:
:If the readings look good I will indoctrinate you how to evaluate the tuning eye tube with merely a bit of Scotch tape and 2 toothpicks or a clarinet reed.
:
:
:Thassit…standing by and waiting for feedback info of experienced voltages:
:
:
:
:
:
:
:
:73's de Edd
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:::Hmmmm....Lewis....how did you get your text to go outside of the text box???
::
::
::I'm not sure, I tried to get cute and put my little switch and bulb thingy, but I hadn't had but one cup of coffee, did something wrong...
::Lewis