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535A CRT in a 575 - clever trick?

Keith
 

So thinking out loud here...It has been pretty well-documented here on the forum in various threads that the 535A scope CRT can be used in a 575 Curve Tracer with a little tweaking. (Pin 8 300vdc connection required, etc.)
The big limitation folks have noted is the 8 cm maximum vertical resolution caused by the closely spaced deflection plates in the 535A CRT. That physical restriction effectively limits the vertical resolution of the curve family at the extremes of the display...by a cm or two anyway.

OK crazy idea.

So, what if one rotated the 535A CRT 90 degrees in the housing and swapped the horizontal and vertical drive inputs to the tube? Wouldn’t that in effect give you a full 10 CM vertical range? (Since the “horizontal” range of the 535 CRT is 10CM... and when physically rotated 90 degrees it is now effectively the “vertical” display area - as far as the scope is concerned.

Of course your horizontal range will be restricted a little but isn’t that less of an issue when your curve tracing?

Or am I missing something here?

CBG

John Williams
 

Good idea. I like things involving older instruments. On Tekwiki the is an incredible document containing every Tek crt spec you can imagine. It is at http://w140.com/tek_crt_data.pdf. It is over 500 pages so be prepared to spend a fair bit of time searching.

Incidentally I was once wondering if the 502 crt was the limiting factor for the 502 bandwidth. Using the distributed amplifier in a 551 I was able to display a 33 MHz sine wave on the 502 crt! Lots of fun. Also there are other Tektronix scopes that use the same crt as the 575.

 

Pity that document doesn't cover the CRTs used in the 7000 series 'scopes.

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of John Williams
Sent: 06 September 2019 21:20
To: TekScopes@groups.io
Subject: Re: [TekScopes] 535A CRT in a 575 - clever trick?

Good idea. I like things involving older instruments. On Tekwiki the is an incredible document containing every Tek crt spec you can imagine. It is at http://w140.com/tek_crt_data.pdf. It is over 500 pages so be prepared to spend a fair bit of time searching.

Incidentally I was once wondering if the 502 crt was the limiting factor for the 502 bandwidth. Using the distributed amplifier in a 551 I was able to display a 33 MHz sine wave on the 502 crt! Lots of fun. Also there are other Tektronix scopes that use the same crt as the 575.

John Williams
 

Could be. There is so much there and at first I was viewing it on my iPad so I wasn’t looking for those tubes. What about Peter Keller’s book? Does it cover the 7000 crts?

Mlynch001
 

You will appreciate the 10 cm vertical range. It makes the math so much easier. The 577 uses an 8 cm vertical x 10cm horizontal display graticule and this is noticeably smaller when compared side by side with the Type 576, which is a 10x10 graticule (with 12cm horizontal, total usable). Seems like a great way to go to me. Either way your calibration will need to compensate for the change in one axis or the other. I read a post from someone that stated that the 577 can be fitted with a 10x10 cm display from some special 5xxx series scope that had this special option and recalibrated accordingly. The 577 supposedly has sufficient trimmer range to accomplish this. I’m fairly confident that the 575 would be able to handle the change as well. All that being said, since a 575 CRT is almost unobtanium, I would sure go this route, rather than having a non-working instrument. Should be able to find a 535A CRT much easier than the 575.

--
Michael Lynch
Dardanelle, AR

ditter2
 

Tek had an option to the 577 that substituted a CRT with a 10 x 10 graticule. The ertical gain adjustment has enough range to handle either CRT.

Substituting CRTs in curve tracers is relatively easy, as BW is not a concern. The maximum BW either deflection system handles is less than 300 Hz, so swapping vertical and horizontal should work, but you do need to make sure the vertical amp has enough voltage swing to handle the deflection. w/o a CRT data sheet, you can determine the required swing by studying the schematics of the vertical and horizontal amps of the scope from which the CRT you plan to use comes from. Tek publishes waveforms at various points in the circuit for troubleshooting purposes. Look at the pk-pk voltages of the amplifiers output, and be sure to check the input conditions. The horizontal is usually the full sweep, but the vertical may be a pulse from ground to a peak level, which only uses half of the CRT dynamic range.

Steve