Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Fairchild 957 O'Scope Display Size  (Read 7124 times)
AC5UP
Member

Posts: 3891




Ignore
« on: October 09, 2012, 08:58:47 AM »

If anyone has experience with one of these I will be impressed....

Many moon ago I picked up a Fairchild 957 rack mount 'scope frame with a 95-71 dual trace vertical amplifier and 74-17A time base. As N4NYY should know, the 'scope was made in Clifton, NJ in the late 60's and there is almost no technical info to be found on the web. I have never seen another Fairchild 'scope despite lurking at many a swap meet - but - I did catch a mention that the time base manual is dated 1967.

Even though it's an impressive piece with a 100 MC vertical bandwidth, it does have some minor issues that might be resolved by condenser replacement. It sat idle for close to 20 years due to a blown fuse in the AC primary circuit. Last night I got a wild hair and looked it over, replaced the fuse, got a sharp blue trace on the screen, and even did a partial tweak on the obvious adjustments like the voltage regulators (clearly marked) as well as the DC Balance and trace centering / geometry adjustments. In many ways it's like a Tek 300 series 'scope although the only tubes are the CRT and maybe 12 Nuvistors.

So, here's the question... Beautiful round 5" CRT with a graticule 6 cm high and 10 cm wide. The vertical amplifier cuts off at the top & bottom of the graticule which means it's entirely possible to get a 'good' display without realizing there's more to be seen. For sweep length I found that 8 cm was about as wide as it wanted to go. Around 9 cm the edges started to fade and didn't look clean, so I figured 6 x 8 cm with a 3 x 4 aspect ratio is where it wants to be. It's a very clean display and I love the blue phosphor........ But..........

This means at least half of the CRT isn't usable.   Is that normal?    Seems a bit tight for a dual-trace / dual sweep 'scope.

Sure, it almost fills the graticule horizontally and does fill it vertically, but that's it. Other 'scopes give plenty of margin around the graticule for signals you just want to look at, not measure, but this one wants to stay inside the graticule markings.    Undecided

BTW:  There's a good chance this one is going to end up being tossed and just for the sheer hell of it I tried installing the two plug-ins bass-ackwards. They aren't indexed and plugged in without a hitch, but damned if it didn't light up and sweep from the top to the bottom of the CRT. I shouldn't have done that, but nothing broke and I did get a grin out of it............
Logged

Never change a password on a Friday                
KE3WD
Member

Posts: 5689




Ignore
« Reply #1 on: October 09, 2012, 09:06:12 AM »

That may just well be a design constraint of the old piece.  I recall that being the case with other high precision, high quality scopes of that era, although I never owned one, the university research labs was my access to them. 

I never thought much about not being able to "use" the entire phosphor at the time, for the amount of detail, etc. certainly overcame such liabilities. 

Likely an effort to avoid the distortions that would surely arise from trying to cover a larger area of the screen, an effort to preserve good linearity.  At least that's my take.

Don't throw it out.  If nothing else, donate it to one of the oscilloscope museums and take a tax deduction...


73
Logged
KD0REQ
Member

Posts: 971




Ignore
« Reply #2 on: October 09, 2012, 10:10:35 AM »

maybe ended up consolidated with DuMont?  iirc a bunch of those high end test equipment makers rolled together for survival when the Japanese invasion started in the mid to late 80s.  Gargled the web for

Dumont Oscilloscope Inc
 
20 Robert St

Parsippany, New Jersey ( NJ) 07054

Phone : 973-334-1410

off powwwerpages.com
 
Logged
AC5UP
Member

Posts: 3891




Ignore
« Reply #3 on: October 09, 2012, 10:51:02 AM »

When I was doing my searches on the web I did find the cross between DuMont / Fairchild, but looking at the test gear itself it looks like DuMont peaked in the 50's & 60's with Fairchild taking the lead toward the late 60's. The 767 appears to be the most popular 'scope Fairchild offered with the 957 as the full bells & whistles model above that. I might snoop around to see what I can find on the 767 as it's similar, although with a single channel time base.

BTW:  Last year I stumbled across a web site with a bunch of vintage pictures from Tektronix and was surprised to learn the typical 500 series 'scope was probably assembled by a woman. Here's a picture of DuMont model 150A 'scopes being assembled and you'll note it's the same deal... Women have smaller hands, possibly better dexterity, and definitely more patience when it comes to precision assembly work.

Note To KE3WD:  I was thinking about donating the 'scope to the Sallustio Institute Of Totally IGGY Test Equipment but decided against it. The 'scope has more than five tubes (metal tubes) and refuses to go back to New Jersey. Can't say I blame it for that....

Here's a picture of N4NYY's sister Vickie doing something Vinnie doesn't understand    Shocked
Logged

Never change a password on a Friday                
N4NYY
Member

Posts: 4799




Ignore
« Reply #4 on: October 09, 2012, 05:48:02 PM »

I have a Tek 8835 scope that the focus went out and was very thick on the beam. I found out thru their groups that 6 carbon resistors in the CRT circuit are notorius for going bad. Sure enough, I found the culprit. Let than $1 of resistors fixed the problem. But I had to purchase $20 of torx drivers to get to the resistors!
Logged
AC5UP
Member

Posts: 3891




Ignore
« Reply #5 on: October 09, 2012, 06:37:02 PM »

BTW:   http://www.shopgoodwill.com/viewItem.asp?ItemID=11558221

Amazin' what shows up in thrift shops..............

In case you're wondering about the pic of your sister testing the two pieces, that's an expensive test bench. The center stack from top to bottom is a nicely optioned Tektronix 1411 video test signal generator / sync generator used by TV stations and studios as the master 'clock' for all video sources. Typically they'd be optioned with the NTSC color bar generator, multiburst generator for checking frequency response, and a ramp / linearity test signal generator like the one in the picture. Below that is a Tektronix 1485R waveform monitor showing both fields of a color bar signal at the 'line' sweep rate. It's essentially a specialized oscilloscope for video testing. Below that is a Tek 650 video monitor with the cross pulse switch set to show the blanking and sync signals between fields in an NTSC video signal. For years that was ' the ' standard video monitor of the industry as it used a custom Trinitron CRT with true NTSC phosphors.

Brand new that stack was worth maybe $30 kilobucks or better, as Tek made good stuff with a price tag to match. Believe it or don't, I own all three from back when I was crazy for video gear. IMHO, no home is complete without a color bar generator.

The two boxes left & right appear to be first generation digital time base correctors. Hence the large number of chips on the visible boards. That's probably RAM and the only thing odd is that each row has 10 chips. Usually it's eight or nine, but if RAM is ten bits wide that allows for eight data bits (very common) plus a parity and stop bit. Which is truly old school. Anyway, helical scan video tape machines present an interesting challenge for television work as they can very easily run slightly out of time relative to other video sources. A TBC stores the video playback signal for a small amount of time just long enough to match the studio sync rate. Some studios used them on satellite receivers as well since they offered a bonus feature of being able to repeat the last good frame whenever the signal glitched. Usually the hold time was so brief that you'd never notice it at home, unless there was some very fast motion on the screen or the signal was loaded with glitches.

The 1411 sync generator in particular had to be dead-on stable as they also provided the master 3.579545 MC "colorburst on black" signal. If that drifted you'd have some commercials a little too green and others a little too purple, which wasn't unusual back in the earliest days of color TV...............
Logged

Never change a password on a Friday                
AC5UP
Member

Posts: 3891




Ignore
« Reply #6 on: October 09, 2012, 06:45:13 PM »

I have a Tek 8835 scope

Didja' mean a 2235A 'scope like this one?

Try Googling an 8835 and you'll come up empty..................  Roll Eyes
Logged

Never change a password on a Friday                
N4NYY
Member

Posts: 4799




Ignore
« Reply #7 on: October 09, 2012, 07:12:55 PM »

I have a Tek 8835 scope

Didja' mean a 2235A 'scope like this one?

Try Googling an 8835 and you'll come up empty..................  Roll Eyes

That is the one. They used all sizes of torx screws. What a pain.
Logged
G3RZP
Member

Posts: 4710




Ignore
« Reply #8 on: October 10, 2012, 02:00:24 AM »

For repetitive industrial tasks, women are far better than men in terms of quality and production speed. It appears that they have a much better ability to multi-task.
Logged
N4NYY
Member

Posts: 4799




Ignore
« Reply #9 on: October 10, 2012, 04:42:58 AM »

For repetitive industrial tasks, women are far better than men in terms of quality and production speed. It appears that they have a much better ability to multi-task.

I can multitask. I can sip beer and change channels on my remote, at the same time.
Logged
AC5UP
Member

Posts: 3891




Ignore
« Reply #10 on: October 10, 2012, 08:16:02 AM »

That's true........ Plus you can look like a doof and act like a doof simultaneously.

BTW:   Mongo no longer pawn in game of life.   <sniff!>
Logged

Never change a password on a Friday                
KA5N
Member

Posts: 4380




Ignore
« Reply #11 on: October 10, 2012, 08:35:15 AM »

Most display problems on  older scopes are caused by resistors changing value.    Many high
value carbon resistors are used in high voltage circuits and simply don't last. 

I would shy away from any instrument using nuvistors, not because they are inferior or failure
prone but because they are rare and replacements will be really difficult to find.

Allen KA5N
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #12 on: October 10, 2012, 09:04:44 AM »

NTSC = Never Twice the Same Color

 Grin
Logged
AC5UP
Member

Posts: 3891




Ignore
« Reply #13 on: October 10, 2012, 09:43:26 AM »

Speaking of........ Have you noticed that video from the web and HDTV in general is usually spot-on as far as color hue and saturation is concerned? The NTSC standard in the US was surpassed by PAL and SECAM in Europe over three decades ago and despite some transition issues, at least DTV brought the world into the same standard.

What most folks don't realize is that when RCA patented their delta pattern tri-color CRT in the early 50's the phosphors were sulfur based. Remember in grade school when you learned about the color wheel? Take any color at any position on the wheel. Let's say red, and vary a few degrees toward yellow or a few degrees toward blue. It's still 'red' in general terms, but not the same red. When color CRT's migrated to rare earth phosphors in the late 60's they gave a brighter and more saturated color rendition but the R-G-B phosphors did not match the original NTSC vectors adopted back in the round tube era.

So, NTSC color has been near the standard for around 40 years but not exactly. In practical terms that's a bit of a nit-pick, but when you see a video signal with matched color vectors at both the camera and monitor it does look more natural. Used to be that yellow was very difficult to get right back in the day as it often drifted toward green, but no longer.........

If your monitor is properly balanced, this should prove the point about yellow...

You've probably heard about the CBS color system, but in 1956 there was a little something called the Philco Apple project that was well ahead of its time:  http://www.earlytelevision.org/apple_crt.html

Note to KA5N:  Many years ago I developed the bad habit of hauling old Tek 500 series 'scopes home from the First Saturday Sidewalk Sale in Dallas. There was a time when a neglected 'scope could be had for $10 or less and I bought them for parts. Phenolic tube sockets (not the wafer kind), sealed potentiometers, Sprague ExtraLytics, and some of the better power transformers ever made. This means the garage used to be packed and I still have a collection of Nuvistors in a little box that I probably couldn't find if I needed to. Never had one go bad, and considering the newer 'scopes I've accumulated, will likely never go back to the Big Iron.
Logged

Never change a password on a Friday                
G3RZP
Member

Posts: 4710




Ignore
« Reply #14 on: October 10, 2012, 10:12:03 AM »

NTSC = Never Twice Same Colour
SECAM = Something Essentially Contrary to the American Method
PAL = Peace At Last


except that there's varieties of PAL......
Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!