6U5/6G5 Tuning Eye Tube Questions
 

Hello everyone I have a question concerning the 6U5/6G5 Tuning Eye tube, for some reason or another I've noticed that when I was working on a late 1950s vintage Magnavox Console (yes the one I accidentally broke the tone control on and that the record player was seized up on so bad that I ended up breaking the speed control knob on it), anyways I noticed that before the tone control broke on it and what not that the tuning eye tube on it responded very well to signals and glowed nice and bright, but then when I gave the unit back to the guy for him to get rid of because it wasn't worth fixing without having to spend a ton of dough trying to hunt down a new tone control switch that may or may not be a proper replacement and having to hunt down a new record player for it, etc, I bought the tubes from the unit off of the guy and I went to try the tuning eye tube from the old magnavox console in my old Well Gardner console from the early 1940s which uses the same exact tuning eye tube as the old magnavox did I noticed that the tube didn't glow as brightly in the Wells Gardner console as it did in the Magnavox and I'm wondering why that is, because the tube is a perfectly good tube yet but yet it don't glow very brightly inside the Wells Gardner Console vs how brightly it glowed in the Magnavox console.
Does anyone know why a tuning eye tube would glow like its supposed to in one radio but not in another radio?

Any info would be appreciated.

-Levi

P.S. the Wells Gardner Console was completely recapped whereas the Magnavox wasn't, so I don't know if that would make a difference or not.

There's usually a resistor (half watt, typically one meg.) hidden inside the socket and it drifts 'waay up in value.

I was thinking of that as a possibility, but how would of that 1 Meg 1/2 Watt Resistor in the Magnavox been still good yet after all these years and yet the one in my 1942 Vintage Wells Gardner Console be bad?

By the way the Tuning Eye tube Socket in the Wells Gardner is a replacement from a 1950s Silvertone Console that was the same vintage as the Magnavox Console was, because the original Tuning Eye Tube socket on the Wells Gardner Console had cloth wires that the insulation was splitting in several spots exposing bare wire and was causing the tuning eye tube to not work at all period. I think I even replaced the original 1 Meg 1/2 watt resistor in that replacement tuning eye tube socket with a carbon film resistor from radio shack and it still wasn't letting the tuning eye tube glow very brightly... :scratch2:

is the eye tube getting its normally specified plate voltage? if that is low it could explain the dim tube.

I don't know about what the plate voltage should be or whether or not its getting its proper plate voltage, I just replaced the socket and went from there not thinking of it when I tested it because all of the tuning eye tubes I had at the time of recapping this old Wells Gardner radio were tubes that were previously used and I was thinking that they were dim because they were maybe heavily used tubes, but when I put the Magnavox tube in place and it was still dim even though it was nice and bright on the Magnavox Console it came out of I knew there had to be something wrong, but as to what I'm not sure because I had previously replaced all of the paper caps and power supply caps in this radio but it didn't seem to help, not even replacing the dropping Resistor in the tuning eye tube socket so there must be something that I had missed in this radio that's causing the tuning eye tube to glow dimly, as to what I'm not sure, and most of the resistors tested within spec yet.

Max plate (pin 2 through 1 meg resistor) and target (pin 4) are listed at 250 volts, although it may have been fairly common practice to push that spec a bit to obtain higher brightness, at the expense of life of the tube.

jr

data sheet: http://www.r-type.org/pdfs/6e5.pdf

OK so how do I go about testing to see if the plate voltage for the tube socket is up to par or not? Should I just remove the tube from the socket and then stick my DMM probes into the right holes for the tube pins to go into and then get a measurement from ground?

So If I were to get a lower plate voltage reading than the specified 250 Volts then what should I look for component wise that could be causing the low plate voltage?

Update: I measured Pin 2 and got a little over 200 Volts (around 208 Volts DC) and at pin 4 I got around 248 Volts DC, So I'm not sure what to make of those results but I'm guessing that both pins 2 and 4 are supposed to measure around ~250 VDC? If so then that means pin 2 isn't getting the proper voltage it needs for some reason which is why the tuning eye tube is dim.

Sounds as if it is working ok... the target voltage (pin4) is the correct voltage, pin 2 is expected to be less, due to the voltage drop accross the 1 meg resistor. I suspect that the Magnavox radio was running with the target voltage above max spec.

jr

OK, that makes sense, also it doesn't help matters any that it has a single 6.3 V pilot lamp right directly above the tuning eye tube for backlighting the tuning dial, that's kind of washing it out a little bit.
Another thing that I've noticed though (and it may be due to the radio not being properly aligned or something like that) but the tuning eye tube doesn't seem to close completely when its on a really close local station, in fact it barely moves at all even though there are like 5 or 6 fairly strong local AM stations that coming loud and clear interference free on the radio, so what would cause the lack of movement on the part of the tuning eye tube's part when it comes to trying to tune in a strong local station?

You can monitor the voltage applied to the grid of the 6E5 (pin 3)... it takes about -8 volts to close the eye completely... if you are not getting that, the agc circuit is possibly not working correctly or signals are weak or set needs alignment. If you are getting -8 volts on the grid when the radio is tuned to a strong station and the eye is not closing, suspect the 1 meg resistor.

Looks like you only have 2 very strong stations:
http://radio-locator.com/cgi-bin/loc...req=&sort=freq

jr

Actually there's about 5 or 6 but 2 of them are stations for the Hispanic community and are in Spanish only, the other one you missed which is AM 960 WSBT which is the local CBS Affiliate's Radio Station, which is News Talk format and has been ever since it went on the air back in the 1940s, there are some others as well that I can get in fairly strong on my Radio like WOWO AM 1190 out of Ft. Wayne (they are a 50kW station that can be heard all across the the country at night), and then then WDND AM 1620 which is a top 40 Hits station, most any AM stations from around the Elkhart, Goshen, South Bend area can be picked up pretty easily on most of my old AM Radios, Also some Ft. Wayne Stations as well.
I'm guessing that the radio may or may not be in need of a realignment because I never touched that part of the radio, all I did was recap the radio and replaced the original tuning eye tube socket with a more modern one, and that was it. I did notice that when the tuner is tuned closer to the bottom of the tuner range the tuner gets really scratchy and noisy almost like the sound a volume or tone control makes when it has dirty contacts.

Did you examine the Radio-Locator chart that I linked to? The chart lists only 2 "Very Strong" stations heard in Elkhart; WCMR 1230 and WTRC 1340, all the rest are listed as "Moderate" to "Very Weak". I would not expect to see full eye closure or even very much movment on a majority of the AM stations that you can receive.

jr

The IFs may have drifted a bit off-peak with age, reducing the gain. It's easy to re-peak them, especially with a tuning eye. Just the barest fraction of a turn either direction will usually get 'em back on peak.

I don't think that chart is very accurate though because most of those stations listed on there (except most of the chicago stations) are fairly powerful stations whoever compliled that chart I don't think did their research properly because I know for a fact that WOWO AM 1190 out of Ft. Wayne, Indiana CAN be heard from almost 2/3 of the country from as far out as the Eastern Seaboard all the way out to the central plains states during the night, and even as far south as Florida, and WSBT AM 960 is a local news/talk station from South Bend, Indiana which is only 12 Miles from where I live and it too has a fairly strong signal because it can be heard all throughout Northern Indiana and Southwestern Lower Michigan farily clearly.
And yes I did look at that chart and I should know about those stations because I've lived in the Michiana Area all my life (27 Years to be exact, because that's how old I am) and I know for a fact that most all of those stations are able to be picked up fairly clearly on most of my vintage radios and stereo equipment I have.

I'll probably give that a try.

The Radio-Locator information presented is calculated from the information presented on the FCC site, using established methods.

FCC data for WSBT:

https://transition.fcc.gov/fcc-bin/a...=0&facid=73985

Note that WSBT is only 5 kW and uses 4 towers to produce a directional pattern, to "protect" other stations.

From this data, the Radio-Locator computer calculates the following coverage map for WSBD:

http://radio-locator.com/cgi-bin/patg?id=WSBT-AM&h=D

Note that Elkhart is near the edge of the "local" plot, and the signal strength is adversely affected by the null in the directional pattern. I would not expect full closure of your 6E5 indicator on that station.

jr

Well I realize its probably not going to completely close the eye, but I'm sure it would at least partially close it because it is considered a local station.
I'm aware that some stations even though they come in clearly won't necessarily completely close the tuning eye tube as I know for a fact that the 6FG6/EM84 tuning eye tube that's on my Silvertone stereo doesn't always completely close for some of the FM Stations near me even though they come in clearly but it does make the eye react enough though when tuning around on the dial none the less even if the station is an incredibly close by station that you know its working.
I know for a fact that the FM counterpart to AM 1270 WCMR here in Elkhart, which is 105.3 FM WCMR which is the FM Stereo version of AM 1270 doesn't completely close my tuning eye on my Silvertone Stereo, but yet the sister station to WCMR, WFRN 104.7 here in Elkhart (which both stations broadcast out of the same building and use the same towers) does in fact completely close the tuning eye tube on my Silvertone stereo, so does 97.7 FM (a local classic rock station out of South Bend, Indiana on the FM Band) and 92.9 (a local pop/top 40 hits station that is also from South Bend, Indiana) also completely closes the tuning eye on my Silvertone stereo as well as does the local country stations, the local 24 Hour Classical Station out of Berrien Springs, Michigan however, although it comes in clearly on the radio doesn't completely close the the tuning eye tube on the Silvertone, so I'm sure that the station's power does somewhat influence whether or not the tuning eye closes completely or not, but that doesn't mean its necessarily not going to come in at all, or not affect the tuning eye tube to some extent.
I have no idea how the AM Band is on the Silvertone and how the tuning eye tube on it reacts with the AM band as the original built-in loopstick antenna inside the stereo for the AM Band broke off of the chassis when I was working on recapping the unit so the AM Band doesn't work on the Silvertone currently until I can get a new loopstick antenna located for it and installed.

But really though trying to suggest that the stations aren't going to affect the tuning eye tube at all is kind of being a little presumptuous because I would think that a properly aligned tuner and properly working tuning eye tube would react to any sort of station its receiving whether or not its an extremely high powered station or not. If the tuning eye tube isn't responding or barely responding even to the most powerful and closely located stations then it has nothing to do with whether or not the station is extremely powerful or not, it has to do with the fact that something on the radio isn't working right whether the tuner is out of whack or the IFs are out of adjustment and need tweaking or something like that then obviously its probably going to affect whether or not the tuning eye tube is sensitive or not to picking up on signals and responding to them.

I think like OldCoot said more than likely the IF cans are out of adjustment and need to be tweaked back into adjustment again and it will probably fix my unresponsive tuning eye tube issue. Because like I said the tuning eye tube barely responds to even the strongest of stations on the AM Band, ironically though it is completely responsive on the SW band even when there's no audible signal being broadcast it picks up on it and completely closes the tuning eye tube on the SW band which tells me its probably something about the AM Band that isn't adjusted properly (whether it be the IF Cans or the Tuning Capacitor or the antenna adjustments.)

If that's the case, the IF stage has adequate gain. Don't mess with the IFs at all.

Then what would cause it to barely respond on the AM Band and Respond extremely well on SW?

When you're on SW, does the eye respond only when a signal is being received? Or does it stay activated somewhat even with no signal received?
If the latter, do you hear a lot of birdies and whistles when turning the dial?

Well the shortwave band is kind of odd because I will sometimes pick up a station from somewhere in Western Europe or even in Mexico or Central America, and the tuning eye will respond to those stations and almost completely close the eye in some cases, what's weird is that when I was picking up some shortwave stations on there one night there was a spot on the SW dial right around the 14-16 MHz area that made the tuning eye tube go completely closed but there wasn't any audio there that I could hear, which was kind of weird but yet when I use it in AM mode the tuning eye tube barely responds even to the stongest local signals, which is got me confused as to why the radio would do that...

Perhaps an un-modulated carrier is what closed the eye....Those are silent.

What's an un-modulated carrier? And are they common in Shortwave Broadcasts?

:no: Okay, really basic radio theory lesson time: Carrier wave = the radio frequency sinusoid that travels through space and normally carries information of some type, Modulation = modification of carrier to place information on it. Un-modulated means no modification of the carrier sinusoid is made.....Just an RF osc. (and probably a power amplifier) randomly radiating power out into space for no good reason.

Types of modulation include CW (turning carrier on and off to represent information normally in the form of Morse code), AM (changing the strength of the carrier instep with a signal that is normally a sound or video signal), FM (changing the frequency of the carrier instep with the signal), PM (changing the phase of the carrier instep with the signal...an integral/differentiation relationship exists between PM and FM signal encoding), QAM (Google it! most common example is color sub-carrier modulation scheme in NTSC TV), and various forms of digital modulation that I don't care to regurgitate, enumerate, and explain.....

As for how common un-modulated carriers are on shortwave...I can't say. It's been a few years since I was a regular SW listener, and even then it's hard to know since many radios (including my favorite SW set) lack a good signal strength meter, and unless the meter is looking directly at RF carrier strength you really have no way to know of their presence with a normal radio unless the band around them is VERY noisy...And even that is not a guarantee of their presence.
The only surefire way to find them is to plop down big bucks for a spectrum analyzer and use that to tune a radio to the frequencies of noticeable carriers....Or attach a measurement device to a TRF radio and learn the difference between atmospheric background noise and carrier waves.

If you don't know how the beast works your not an electronic technician, but a mechanic/parts swaper.

I have a basic running knowledge of how radios work but as far as why they do some of the strange things they do sometimes that I don't understand (after all I'm going to school for computer repair not electronics repair, seeing as electronics repair is more or less a dead artform since everything is more or less juts throwaway now, because I was born about 3 decades too late for electronics repair classes of any sort and I mainly dabble with radio and record player repair as a side hobby.)

Also there still hasn't been any definitive answers given yet as to why the tuning eye tube on my radio would be more sensitive on the Shortwave band than on Broadcast (AM) band, especially seeing as I've figured out that the tuning eye socket is getting the proper voltages its supposed to have but yet it barely responds on the AM Band but responds extremely well on the SW Band.