Eye Tube 6U5

1/26/2009 8:56:34 PMSteve

I have a 6U5 tube in a Zenith 7-S-636 that is dark. The filament is lit but the eye is dark. I've tested the tube on my tube tester and the eye does light but isn’t very bright. I have the following voltages on the tube. Reading the socket and going CCW. Pin 1 to Pin 6 6.5VAC. Pin 2 to chassis ground 213VDC. Pin 3 to ground -.04. Pin 4 to ground 180. Pin 5 to ground -1. Are these voltages in range?
Steve

1/26/2009 9:35:13 PMThomas Dermody

It is typical for eye tubes to go dark and still test 'good.' There is something about their design that causes the phosphor to burn out rather rapidly. I wonder if it is anything similar to what happens to a television tube when no ion trap is present.

Anyway, it's time for you to purchase a new tube. If you really want to save the original tube, you can put a voltage doubler in your set's HV circuit, or find a higher potential B source in your set to feed the eye tube. However, I recommend purchasing a new tube and just running it at its recommended voltage.

I have said this over and over that it is amazing how the vacuum fluorescent displays in microwaves, cars, VCRs, and the like, last for years and years with good brilliance, but magic eye tubes seem to lose quite a bit of their brilliance after only about a year of somewhat regular use. Some tubes last longer than others, but they definitely have a quick half life. Tubes that I've put in some of my radios only 5 years ago are quite dark now, and used to be almost too bright when they were new.

1/26/2009 11:03:11 PMWarren

This guy here has NOS 6AB5/6N5 magic eye tubes for $16.50 .. Should work in place of a 6U5

http://bensradioattic.com/fleamarket.php

1/27/2009 8:06:39 AMSteve

Looks like it's time for a new eye tube. Thanks for everyone's help.
Steve

1/28/2009 1:24:46 AMplanigan

Those tubes, unfortunately, had an expected life expectancy of 1000 hours only.PL

:Looks like it's time for a new eye tube. Thanks for everyone's help.
:Steve

1/31/2009 11:20:45 AMdave

ive thought about installing a small switch(in line with the heater ? ) so the eye could be turned off, but never have. one radio i can reach in and unplug it,..but another has the eye buried deep in the chassis

: Those tubes, unfortunately, had an expected life expectancy of 1000 hours only.PL
:
:
::Looks like it's time for a new eye tube. Thanks for everyone's help.
::Steve

1/31/2009 12:54:54 PMWarren

Years ago I did just about that with a Packard Bell.
The tone control had a cracked disk, I replaced it with a new pot that also had a pull on, push off switch. Was able to use the switch to turn off the heater, the radio still looks stock.

1/31/2009 6:31:47 PMZ-

:This guy here has NOS 6AB5/6N5 magic eye tubes for $16.50 .. Should work in place of a 6U5

The 6N5 is not an ideal subsitute. This tube is designed for AA5 radios types, those without transformers, hence the lower plate voltage. The tube is designed to work at 135V with a max plate voltage of 180V. Using this tube at close to max will surely shorten it's usable life.

Syl