|
Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
|
Thread Tools |
23rd Oct 2014, 3:07 pm | #21 |
Pentode
Join Date: May 2014
Location: Amsterdam, Netherlands
Posts: 202
|
Re: EM34 magic eye
Don't forget CRTs have a much larger area and are only written to very briefly (when the electron beam passes a particular spot). CRTs will burn if deflection fails.
A magic eye is full on all the time, dramatically reducing life time. I don't believe ion burn causes the eyes to go dim. Voltages are too low for that I'd say. Tjerk, 9ZZ |
23rd Oct 2014, 3:16 pm | #22 |
Hexode
Join Date: Jul 2014
Location: Magor, Monmouthshire, Wales, UK.
Posts: 436
|
Re: EM34 magic eye
At risk of going off topic, I've never come across an EM84 type with the phosphor on the envelope glass that has faded, just my luck or is there a correlation?
__________________
Adapt, Improvise, Oh Bother..... |
23rd Oct 2014, 3:34 pm | #23 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
|
Re: EM34 magic eye
They do hold up well- but I have seen some very weary and dim EM84s. Perhaps it's a better scheme to have phosphor on glass, rather than on a metal backing. I reckon it's not a bad idea to remove them for day-to-day background use and keep them to low hours for show- bearing in mind price ande availability. Some sets with variable selectivity only applied HT at minimum bandwidth for precise tuning.
|
23rd Oct 2014, 3:45 pm | #24 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,549
|
Re: EM34 magic eye
I have got a resistance bridge with a magic eye for balancing.
It has a switch to turn it off while the instrument is powered and waiting for use. |
23rd Oct 2014, 9:05 pm | #25 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
|
Re: EM34 magic eye
|
23rd Oct 2014, 9:15 pm | #26 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,801
|
Re: EM34 magic eye
I saw aluminising sold as a means of avoiding phosphor burn and allowing more energetic beams. In scope tubes it came along with PDAs.
David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
24th Oct 2014, 9:22 am | #27 | |
Octode
Join Date: Mar 2006
Location: Lund, Sweden
Posts: 1,631
|
Re: EM34 magic eye
Quote:
Plus the public would have been used to the concept of magic eyes from radios. And using an overlap point in the resulting image is actually a rather accurate way of seeing when things go above a certain level. As a side effect, a magic eye is inherently peak reading, and since distortion happens at the peaks, it makes sense for a domestic recorder to have a peak reading recording level indicator. For professionals, who can better judge the amount of peaks in the programme material, and have a better grip on tape distortion, a VU meter might be better to get maximum usage from the tape. Tandberg stayed with magic eyes a bit into the transistor technology era for precisely this reason (Tandberg model 12). Once they went to meters, they had appropriate drive circuits so that they were peak reading (most noticeable in 70's machines such as the 3300X or 9100X where PEAK READING is even printed on the meter). This was the late 60's, so by then an additional transistor to drive the meter cost peanuts. In terms of cost-cutting, it has always struck me that European recorders most often had magic eyes for recording level indicators, whereas American machines at least in the 50's tended to have a couple of neon lamps for this purpose, one flashing at 0dB, and one a bit over. That must have been even cheaper than a magic eye, and I think the US market especially in that era was more price sensitive then in Europe. |
|
24th Oct 2014, 10:53 am | #28 |
Pentode
Join Date: Jun 2008
Location: London, UK.
Posts: 157
|
Re: EM34 magic eye
I've recently been lucky with acquiring an EM1 for my '39 Philips that I've had for years and the eye never worked. I got it for a tenner (plus postage from S America) It is absolutely lovely, so bright and the first time I've ever seen one working.
As it is brighter than required, I'm interested in Restoration73's idea of perhaps half-wave rectified mains fed to the target. What are peoples' thoughts on this? Possibly a switch to cut off target volts while playing the set for long periods? |
24th Oct 2014, 11:03 am | #29 |
Nonode
Join Date: Jun 2009
Location: Herefordshire, UK.
Posts: 2,495
|
Re: EM34 magic eye
Re: post no 27,
... and remember that 50s and 60s tape oxide formulations were not so forgiving of transient overloads - so a fast responding magic eye made sense... |
31st Jan 2015, 8:15 pm | #30 | |
Nonode
Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 2,853
|
Re: EM34 magic eye
Quote:
I have two EM84s, one from an Elizabethan LZ29, the second from a Robuk RK4 (first version), and both are showing some phosphor degradation - in bright artificial light or daylight you can see a brownish/grey tinge to the illuminated parts of the phosphor when no power is applied! Surprisingly, the Robuk had the worst one even tho' its target-anode (pin 6) is not operated at H.T. voltage but at about 155-165V with a 100K feed resistor. Chris Williams
__________________
It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! |
|
31st Jan 2015, 9:33 pm | #31 |
Heptode
Join Date: Dec 2014
Location: Limerick, Ireland.
Posts: 901
|
Re: EM34 magic eye
Higher HT, non-intuitively is lower wear!
Yes the later blue-green and phosphor on glass to degrade, just same as a new VFD panel in DVD/HiFi/Cooker does (same triode tech but lower voltage, like a DM160). It's just that the Emerald green (EM34 and similar) degrade MUCH faster. The Russian Octal doesn't have same Eye pattern as an EM34, but otherwise is similar. If the gain is too high then the driving grid can have an attenuator. It needs an adaptor or base rewiring anyway. About 1/10th price or less for NOS. |
1st Feb 2015, 12:21 am | #32 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
|
Re: EM34 magic eye
Why is higher HT lower wear, Mike W? I'm intrigued...
|
1st Feb 2015, 12:55 pm | #33 |
Heptode
Join Date: Dec 2014
Location: Limerick, Ireland.
Posts: 901
|
Re: EM34 magic eye
The problem is though that the "crt" grid isn't accessible (it's usually tied to cathode), so to reduce the target beam current you need to reduce heater voltage.
On the other magic eye thread I put the link to Radiomusuem.org article. I'm sceptical myself, but the person making the claim is a "tube guru". I'll look again for the link |
1st Feb 2015, 5:27 pm | #34 |
Heptode
Join Date: Dec 2014
Location: Limerick, Ireland.
Posts: 901
|
Re: EM34 magic eye
Lighting up dark eyes
http://www.radiomuseum.org/forum/lig...eye_tubes.html Life span question (phosphor) http://www.radiomuseum.org/forum/lif...magic_eye.html How it works http://www.radiomuseum.org/forum/how...ors_works.html Operation of very different principle DM70 / DM71 http://www.radiomuseum.org/forum/dm70_operation.html Other links http://www.radiomuseum.org/forum/rep..._the_6e5c.html http://www.radiomuseum.org/forum/rep..._the_6e5c.html http://www.radiomuseum.org/forum/mag..._patterns.html Russian 6e1p Angel pattern http://www.radiomuseum.org/forum/how...4_or_em87.html Best dedicated site on Magic Eyes (He is also a Radiomuseum.org member) http://www.magiceyetubes.com/patterns.htm Comprehensive history of Tuning Indicators http://www.radiomuseum.org/forum/his...c_eye_led.html |