EM81 tuning eye, how bright is bright?

[ekjdm14]

Just a couple of photos of the EM81 tuning eye in Laurence's Bush VHF61. The set is a really nice example, I'd say a low-hour survivor well stored and in exceptionally clean condition. I would expect that my hands are only the second or third pair to venture inside the chassis since it was new, the only evidence of previous work being the ECH81 replaced with a Mazda item, and the VHF plug had been cut off for some reason, literally nothing else had been touched.

The question is, how bright would the eye have been when new? I ask since Laurence is considering whether or not to invest in a new one to complete the set, which would be very close to mint in my view.

Personally I feel that it's working perfectly well, but having no experience of how bright it would have been when new I don't know. Obviously hard to say from photos but to my inexpert eye I'd say with the eye fully closed on Radio 2 it's approximately half as bright as the scale lamp. Visible but not overpowering, I may have a differing opinion when it's light outside but anyway enough rambling.

What do those in the know have to say about the brightness of these valves when new?

Cheers,

[paulsherwin]

As you say, it's difficult to tell from the photos, but that looks OK to me. Magic eyes aren't especially bright even when brand new, especially if the ambient light levels are high.

[ekjdm14]

Thanks Paul. Considering the price of new EM81's I'd call it more than acceptable. Pretty easy to change part anyway, being spring mounted, shame it's not an EM84 though as they seem a lot cheaper to the point of being a bargain!

[Argus25]

Not exactly the same, but I use 6u5 magic eyes as defacto VU meters on my valve stereo amps, dating back to the 1970's. Over many years I collected and tested many brands of these. In their case there is a very wide variation of brightness from types made by different manufacturers. I'm not sure if this would be the case for EM81's and there was a reason why it was the case for 6U5's.

Many early versions had a very sparse coating of green phosphor on the target, especially all the early manufacture types. You can tell by looking at them, the target looks almost like silver- grey metal when not illuminated. Later some eyes started to appear, marketed as Tronix brand in the UK (I think they might have been of Japanese origin), which had much more phosphor on the target. When they are off the target looks white, and when on running vivid green and about 4 x as bright as the originals. Later some Toyo ones turned up that were just as good on ebay.

Also, I found the life of the very bright ones was greatly extended if the target voltage was reduced (they were still brighter than the originals), but if you go too far the illumination breaks up and goes blotchy.

I will take a photo sometime today and post it to show the sort of brightness. But as I say for 6u5's at least, it is very manufacturer dependent, even for a new part.

[Boater Sam]

Not seen one significantly better than that.
EM87 are cheap too!

[Nickthedentist]

Originally Posted by ekjdm14

T...shame it's not an EM84 though as they seem a lot cheaper to the point of being a bargain!

You can fit an EM84 easily enough. They don't look right, but they give off that evocative green glow which counts for a lot.

[ekjdm14]

The one in place is a Mullard, will see what it looks like in daylight & think more on it then.

Thanks for the speedy replies though, it's interesting to note that manufacturer can play a part in initial performance. I think this one has a silvery-grey look to it a little like sandblasted steel so perhaps not a "blinder" even new...

I did look at the data for the EM84 but I agree it wouldn't look right. Personal preference in play, but the only ones that really appeal to me are the ones like this with a "V" that closes & the end-viewing ones with a closing semicircle.

[paulsherwin]

The EM84 was the recommended trade substitute after the EM81 became obsolete, but it always looks a bit of a bodge. It's a pity as EM84s are particularly durable and there are lots of pulls from 60s tape recorders around.

All the metallic target eyes I've come across have the same light grey target colour, sometimes with faint burn marks after a lot of use.

[martin.m]

The EM81 in post #1 looks nice and bright to me. I have a VHF61 and the original "magic eye" was very dim. The one pictured came from a scrap Grundig TK5 tape recorder circa 1956.

[G8UWM-MildMartin]

That looks good.
The cheap ex-USSR 6E1P would be an acceptable direct replacement when it eventually fades away.

[Argus25]

I have attached a couple of photos of the eyes used in my home stereo amplifiers.The eyes are driven by the audio envelope (rectified and partially filtered) so they wink in time with the music.

They are particularly vivid, 6E5's. Actually I posted an ebay link to these eyes on this forum a long time ago, but the mods scrubbed it because it was an ebay reference. These types have a white looking target before they are energized.They are at least 4 times as bright as RCA's originals.

(About the amps in the photo, they are modified Seeburg ultra-linear juke box amps with pairs of 6L6's that I configured for a home stereo when I was 16. They have an astonishingly clever optional volume leveler circuit in them which modifies the behavior of a pentode to behave as a variable resistance. In operation it allows for the changes in average level of many different recordings, it works so well you would swear you were adjusting the volume control manually to the same average level for each recording. The eyes are non standard of course , I added them in a spare socket for a bit of fun. This amp is fed by a Quad 34 preamp)

ps: you can get an idea of the brightness of the eyes by looking at the filaments of the 5U4's.

[ricard]

In general, I would say the translucent ones like the EM84 and EM87 are brighter than the reflective ones like the EM80 and EM81. The one in the OP's posting seems to me to be as bright as one would expect of that type.

Speaking of which ... there's something slightly odd here. The EM81 is like the EM71 in that there are two green fields which grow from the sides and eventually meet in the middle, potentially with some overlap. They were favoured by certain brands of tape recorder as recording level meters, Philips is the one that primarily comes to mind. A lot of other tape recorder manufacturers such as Grundig and Tandberg used the EM71 in that era for that purpose. When the fields overlap, creating a brighter central overlapping area, it would indicate tape overload, an excellent and intuitive way of doing so.

The EM80 has an in some respects inverted image, with basically a thin vertical line which widens like a fan when the signal increases. Hence, the German name for it is 'magiches Fächer' (magic fan) This page: http://www.sm5cbw.se/tubes/eyes.htm has lovely animated images of the various types. In my experience the EM80 was preferred over the EM81 as a tuning indicator, possibly because it used a slightly simpler graphic metafor - the more, the better - rather than two fields that were reaching out to each other.

In fact, the EM80 is really two EM81-type fields at right angles to each other, with the right part of the left field merging with the left part of the right field to create the central 'fan'; if you look at the animated image for this valve at the above link, you'll see how there are two smaller fields on each side that reach up and eventuallly make contact with the main central 'fan'.

So what I'm trying to say with the long-winded explanation is that the EM81 would be rather unusual for radios, as would the EM80 for tape recorders.