Which 'Scope was this?? - Page 1
Forum section: electronics / testgear

author: Sparc
author_rank: Contributor
timestamp: November 24, 2013, 10:14:21 pm
content: Hi. I was thinking about an oscilloscope I briefly used many years ago. It was long ago and I didn't pay attention to the make or model at the time. The recollection of this scope still sticks in my mind. I was wondering if anyone could help me identify who made it and the model?It was a vacuum tube based scope, but was fairly compact, so I guess it was probably built at the end of the tube era. It had a feature that I still think is very unique. The horizontal timebase was selected with 2 decade knobs and a multiplier. For example, 37 microseconds/div could be selected by setting the first knob to (3), the second knob to (7), and the multiplier to (1) microsecond. The other aspect I remember was the phosphors. The scope had the most beautiful, brilliant, royal-blue colored phosphors. Really striking compared to the blue-green phosphor that are common.Thanks for any replies, maybe someone can jog my memory or knows what this scope was.

author: tautech
author_rank: Super Contributor
timestamp: November 25, 2013, 03:41:44 am
content: How many years ago?UK Telequipment (acquired by Tek) had a crisp blue trace."The horizontal timebase was selected with 2 decade knobs and a multiplier. For example, 37 microseconds/div could be selected by setting the first knob to (3), the second knob to (7), and the multiplier to (1) microsecond."Was this just a dual delayed timebase?

author: Sparc
author_rank: Contributor
timestamp: November 25, 2013, 10:17:11 am
content: Quote from: tautech on November 25, 2013, 03:41:44 amThis was in the late 90's that I used the scope. (I'm not too old, LOL). The scope must have been pretty old then. The scope used tubes for its internal amplifiers and circuitry.I don't think it was a dual delayed timebase. As best I remember, the primary timebase was selected with these 2 decade knobs and multiplier.Thinking about it, that does sound really unusual. Perhaps you are right and it was a delayed timebase. But, I don't remember a "simple" primary timebase with the usual 1-2-5-10... sequence. I remember being impressed with the flexibility of such fine adjustments to the horizontal, but at the same time being annoyed having to rotate so many knobs just to get 2.0 ms/div for example. (and then not being sure if it was 2ms or 200us/div because of how the multiplier was arranged!).I searched Google images for UK telequipment, but didn't see anything that looked similar.

author: tautech
author_rank: Super Contributor
timestamp: November 25, 2013, 11:44:29 am
content: Vacuum tube amps wow. That will be going back a bit. Ones i have had went back to late 60's but no tubes, all discretes with linear supplies. I have come across museums online in the past searching for manuals and parts for old scopes. Didn't save any links though.I'm sure some other old bugger like me will have some info.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 25, 2013, 12:16:03 pm
content: Sounds a bit like a Tek 524AD.They had a strange combination of dials to set the time/div.Was it very large?

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 25, 2013, 12:24:01 pm
content: That's indeed a fascinating way of setting the timebase.It's just that as far as I can see they have a green tube, not blue.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: November 25, 2013, 03:04:58 pm
content: Tek offered a CRT with blue phosphor as an option for some models (one of the 7000 series mainframes that I am certain of). This was due to the different persistence between colors. Finding these are hard though, they were never common to begin with.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 25, 2013, 04:04:42 pm
content: After some thinking about it,my memory seems at odds with the pictures on the 'Net.The 524AD had a very dense green filter,which when fitted,made the trace appear as the traditional green.Someone had removed this filter to obtain a brighter trace for use with a CRT camera.The tracewasa "greenish -blue",(not nearly as intense blue as later models,though).

author: PaulAm
author_rank: Frequent Contributor
timestamp: November 25, 2013, 04:19:15 pm
content: Different phosphors were sometimes available as options. P7 is blue, but not common. P31 is sometimes seen, but I think P2 was the standard blue/green phosphor. P1 was also popular.I think P7 was popular when you used a scope camera.

author: Sparc
author_rank: Contributor
timestamp: November 26, 2013, 04:32:00 am
content: Quote from: vk6zgo on November 25, 2013, 12:16:03 pmYou might have identified it. The 524AD looks bigger than I remember, but this is probably it. Downloading a manual from the net, the Tek 524AD has continuous timebase control from 0.01 sec to 0.1 us . It looks like the left decade was a ten position switch and the right decade was a continuously variable potentiometer. It probably had the P11 blue phosphor. I've occasionally remembered this old scope and I'm glad to find which one it is. Thanks!

author: N2IXK
author_rank: Frequent Contributor
timestamp: November 26, 2013, 09:17:43 pm
content: The blue phosphor was P11. Usually used with a Polaroid scope camera for permanent waveform recording in the days before digital storage scopes.The original oscilloscope phosphor was P1 green. This was the standard for a long time, but was eventually replaced by the blue/green P31, which was more resistant to phosphor burn at the higher accelerating voltages that came into use as bandwidth and writing rates increased.P7 is an interesting "dual layer" screen, developed originally for radar. It has a very short blue/white fluorescence while being hit by the electrons, and a very long (several seconds) persistence yellow/orange phosphorescence afterward. Usually used with an orange filter to suppress the original blue flash.A fairly comprehensive list of CRT phosphors is available here:www.bunkerofdoom.com/tubes/crt/crt_phosphor_research.pdfTektronix made their own CRTs, and could supply most types with any phosphor you wanted for a fee.