[hsusmann]

I am working on an RCA model 10T from about 1935. It's got
a 6E5 eye tube which is a bit dim.

The owner is willing to spring for a NOS 6E5 and I am thinking
that I should do something to enable the tube to be switched
off to save it's life in the future.

So, my idea is to bring a switch out the back somewhere
that switches off the filament voltage to the 6E5.

Does anyone see any problem with doing this? I don't think
anything bad will happen to the tube if the plate voltage etc..
is there when the filament is cold or am I wrong?

I would appreciate any thoughts...

Herb S.
Ithaca NY

[morzh]

This guy keeps selling these (or this).

http://www.ebay.com/itm/Magic-Eye-Tube-A...4acf77385c

[hsusmann]

morzh,

Yes, I suppose I could just switch the socket over to an octal.
I did not look up the price of the other eye tubes to see if
they were much cheaper. I will do that now. I was assuming that
all eye tubes were about the same price but it seems not?

I like the idea of being able to power down the tube to save it.
Most of the time it just sits there burning phosphor and serving
no purpose except "looking cool".

Herb

[morzh]

No...not all.
6E5 is about the cheapest from that series (I do not count the short ones), and even Russian octal versions are on an order of 18 bucks or so plus hipping from somewhere in Bulgaria.
6U5 which is drop-in but less sensitive is more expensive (it is electrically the same as 6T5, this is why you will see it in Zs).

But take 6T5, the one that came with Zeniths originally.....those even well-used are above $100. They are rare.
In a year I only saw one on eBay.
Right now there is one NOS being auctioned....it is already $125.

[hsusmann]

Well, I went on eBay and found one that was claimed to be "very bright" for $20 + $5 shipping so I Bought it Now. Seems simpler for the time being than going with something like a 1629 with a voltage doubler etc...

[morzh]

Yes. I also went with 6E5 when I needed replacement.

[Conelrad]

Most of the old eye tubes I've seen died from too much direct sun exposure, rather than emission failure.

The coating has more than one way to emit....

Dennis

[hsusmann]

Conelrad,

OK, that is interesting. I suppose there are a couple of failure/wearout
modes going on:

1. Cathode emissions decline with use
2. Phosphor degradation with normal use

I wonder if some of the phosphor degradation might not come
from ion bombardment rather than electron bombardment.
As far as I know there is no mechanism in these tubes to
divert the ions away from the screeen as in old style CRTs
with the ion traps etc...

And now this about sunlight on the phosphor. I had not thought
about that one!

Thanks,

Herb

[Mondial]

There seems to be some controversy regarding sunlight damage to eye tubes. Here is a link to someone who left an eye tube outside in direct sunlight for years with no apparent ill effects.

http://www.dialcover.com/eyetube.html

[morzh]

I tell you this:

My Melodyia radio
http://www.rw6ase.narod.ru/000/rpl_s/melodija_rprl.html
was about 30 years old when we left in 1989 and left it behind (you do not emigrate in the US going through two other countries bringing your monster of a radio with you).
The eye tube, 6E5S (6E5C in Soviet designation) which is octal 6E5, while probably not being super bright anymore, was bright enough, quite green with a very nicely discernible sector.
It was exposed to whatever sunlight we have in all places we lived, and it was always in a brightly Sun-lit rooms.

I am not sure how sunlight could do anything bad enough considering that window glass blocks major part of UV rays.

[Arran]

I think that you could work it one of three ways, switch off the B+ voltage, switch off the filament voltage, or switch off the cathode connection. Switching the cathode connection won't work on many tubes because it is connected to the same pin as one end of the filament. I have an RCA that had a defective 6U5 socket where the B+ voltage lost it's connection to the target, the filament stayed connected, the result was a reasonably bright target but a weak testing triode. I would go with switching off the tube heater/filament, it's bad for a tube to be run for long periods without a plate voltage. In fact many Am/Fm receivers switched off the B+ to some tubes which resulted in them becoming stone cold dead for emissions.
Most of the eye tubes i run into are originals, the owners never replaced them, why? Because they are a gimmick, so it's no surprise that most are worn out.
If I had a set that used an American 6E5 I would probably get either a NOS or a good used tube, unlike the 6U5s they weren't used in as many radios. Contrary to popular belief you can run a 1629 on 6.3 volts without any ill effects if it has good emissions, it just takes longer to warm up, but you still need an adapter. However while the 1629 and Soviet 6E5s both have octal bases the pin-outs are completely different. You can still get Soviet 6E5s for a reasonable price but I can't see the advantage of using them unless you can get them in lots, by the time you make an adapter or replace the socket you will have more into it then just buying the proper American 6E5, even without the shipping cost.
Regards
Arran