Tektronix 585A 100Mhz analogue valve scope issues.

[Diabolical Artificer]

I've had this big old scope for a year or two when one day it clicked off, the main fuse had blown. After many weeks of testing trying to find a short i found two windings, the 140v and dual 114v had a SC across them. Getting this far took some time as I couldn't do the usual turn it on and take some voltage readings because after 40 seconds or so when the soft start relay kicked in, the main fuse would instantly blow.

After finding the SC I then spent another few days chasing red herrings down rabbit holes, as Dave Jones says. Managed to fix that issue and have now thanks to the immense kindness of a chap off UKVRR, have replaced the mains tfmr and will power it up this morning. After that i'll attempt to go through the maintainance and calibration sequence in order to check every function, or at least as far as possible with what gear I have.

I've done some video's here, starting with part 1 - https://www.youtube.com/watch?v=ULeXcKUTKBg&t=4s . no idea why i bother with these video's to be honest, I get about 10 views and most folk switch off half way through. Scratch that, i know why I do these video's, A) to share my passion for these old scopes B) to help folk in the future, even though I haven't a clue what I'm doing half the time C ) Trying to turn folk on to these old scopes and hopefully preserve a few that would otherwise get stripped of their valves and scrapped.

Please let us know what you think of these video's, don't hold back, if you think they're cr*p say so. I'm not the best videoblogger and find myself rabbiting on talking out of my pipe, it's actually quite hard to do: fix a complicated bit of gear whilst narrating in an interesting way and remembering to frame the picture properly.

Andy.

[ppppenguin]

The 585 series scopes were an attempt by Tek to make a general purpose 100MHz scope using valves. This was far from simple, even for Tek, and they never quite managed it. They could only guarantee 85MHz in the end. I owned a 585 many years ago and it was a troublesome beast. Seemed like everything was sacrified against the great god of bandwidth. Compare the 585 against the 547 which was the last generation of 500 series scope. The 547 may have issues with its EHT transformer but is a great 50MHz scope. I have one under the bench and it's lovely. But I never seem to have any reason to use it. The 453 and 454 solid state scopes showed the way to the future. 150MHz BW was a world beater and it was easily portable.

It should have been possible to find the mains TX fault by cold testing with a Megger. But Andy was there and I was not.

[Diabolical Artificer]

I was under the impression the 585A was the last 500 series scope Jeffrey, sure I read that somewhere however I just went looking and found this page - https://w140.com/tekwiki/wiki/500-series_scopes - interestingly it lists the 580 types separately.

What's cold testing? Presume it's with the scope not powered up. I found the tfmr fault eventually with a Megger of sorts, an Airmec Type 251 Ionisation tester, see video one, though I use it in that vid as a voltage source only not an insulation tester.

Andy.

[ppppenguin]

The 580 series weren't really part of the original 500 series. You can use 500 series plugins in a 580 series scope but you need a special adaptor, type 81. In my 1967 Tek catalogue the 580 series are in a different section to the 500 series. The 580 series are decribed as 85MHz in that catalogue. Some sources, including the tekwiki, say 100MHz but that was Tek's hope for the design. Getting 100MHz BW from the input socket to the CRT proved to be impossible to maintain in production.

Cold testing is indeed doing it without power applied. The insulation failure might have been apparent at low voltage from an ordinary DMM or it might have needed a high voltage to show it. Using a Megger or similar is fairly safe as the current is very limited. A crude and not very safe method is mains and a low wattage bulb. Will show serious insulation failure but not minor leakage.

[ppppenguin]

IMO, a 580 series scope is really only for the dedicated test gear enthusiast. From personal experience it's not a good general purpose scope.

The 545 (and later A and B versions) was the real classic. Others in the 500 series used the same plugins. The 547 was the best of the lot. Though you'd need to be real enthusiast to keep a humble 531 in service. All 500 and 580 scopes are full of 6DJ8 (ECC88) valves with the result they are worth more for their valves than as complete scopes.

[Diabolical Artificer]

"You can use 500 series plugins in a 580 series scope but you need a special adaptor" Yes, the McMurdo red range chassis connector is upside in relation the the Tek 545 etc. "IMO, a 580 series scope is really only for the dedicated test gear enthusiast" My 585A has better frequency response than my Tek SC502, flat from DC to over 100khz which is the range I'm mostly interested in, the Type 82 plugin also has a 50v/div capability as well a 450v IP limit ideal for testing valve circuits and lastly it warms the workshop up a treat : ) so it's a good for my purposes, not used a 545 but I have a few which hopefully I'll get running soon.

Andy.

[ppppenguin]

Don't understand your comparison with the SC502. I looked it up and it's a 15MHz scope. So it will be flat to several MHz.

A 545, especially with a 1A2 or 1A4 plugin, is a better general purpose instrument than a 580 series.

For valve work with a modern scope that only goes to 5V/div the answer is a 100:1 probe. I must get one or 2, though finding a half decent one at a reasonable price is another question.