Tektronix 545A 'Scope: 'HT' Metal Covers

[Anthony]

Does anyone have the High-Voltage Metal covers for this 'scope. I may have to make them from aluminium sheet but originals would be great. Thank you.

[m0cemdave]

I have an EHT cover plate but I can't remember exactly which model it was from.
Dimensions are 225 L x 82 W x 55 H.
If it looks like it will fit, you're welcome to it for just the postage cost.

edit to add:
Iit looks a lot better than the pictures!

[Anthony]

Dave

This is really kind of you. From your photo it looks like it will need a lot of battering-about to make it fit my poor old 545A. I really would hate to butcher it and might as well start with some aluminium sheet. I am not so familiar with Tek scopes that I can identify your one. But thank you very much for the kind offer.

Anthony

[Diabolical Artificer]

I have the one in the pics, dimensions 5" wide, 5 5/8" long top, 2 3/4" deep, it's off a 545B, I think, your's for the postage. Drop me a PM if interested.

Andy.

[cmjones01]

Andy's one looks like what's in my 535A, so it may well fit a 545A. I like that part because it includes the words "EVEN MORE DANGEROUS" in red capital letters, which is always nice to see!

I used to own a 549 which had had a replacement EHT transformer fitted and someone had lost the cover. I made a new one from aluminium sheet, but an original part is much nicer.

Chris

[Anthony]

PM sent to Andy

[Anthony]

Chris. Yes. I am suitably terrified of both what Tek call the LT at 500V and HT @ 10kV.

[Craig Sawyers]

The 500V and 350V lines are indeed the dangerous ones, because they supply substantial current.

The old saying "volts jolts, current kills" is quite true in a classic era Tektronix valved scope.

Craig

[Diabolical Artificer]

PM replied to.

Never had a belt off a Tek 500 series valve scope. Everything is so beautifully built & laid out they are easy to work on for the most part. The -1300v test point is iffy though. There's a hole in the EHT cover you can probe through but as the cover is at ground potential and it's tricky to hit the TP with a probe it's easy to slip and create a SC.

I always take the EHT cover off when checking the EHT, you need to anyway to check the 8.5kv supply.

Andy.

[Anthony]

Andy

Thank you for that tip. Working on the HT of my first 545A, I have kept all covers off and fingers well away. I have been on the look-out for pops and bangs and smells and had a few but it seems to have all settled down now. Long story with replaced Ht txfmr, various caps and perhaps duff joints. I am still not sure just what has been going on. I really do not like working on that bit, though, as you say, the construction quality is fantastic. I have some proper silver solder and finally settled on a tip which seems to work on the ceramic insulator connections - they are fussy. Yes? Anthony

[high_vacuum_house]

What a coincidence! I have both of the EHT system covers missing on the Tektronix 545A that I am currently finishing off and was going to see if there was a scrap one in a shed somewhere!!. They are identical to Diabolical Artificer's covers.

Were they to keep curious fingers out of the exposed HV multipliers or as a screening can (or both!) as there is a slight wiggle on the verticals when displaying a square wave! and wondered if the missing covers were to blame!

I intend to do a write up soon once completed. It is nice and cosy with half a kilowatt of valve heaters on the go!!
I have had to change out all of the bumblebee capacitors (wax paper type) and all of the capacitors in the EHT multiplier and cathode/focus circuits.
Cleaning the knobs this evening in the kitchen sink and only a few odd tasks to do before it is complete.

Christopher Capener

[Anthony]

Chris. Yes. What a coincidence. Not sure why someone wouldn't bother to replace the covers but I suppose we have all done that. The EHT caps are tricky to get at and i have only replaced one so far. Anthony

[m0cemdave]

Does anybody recognise which Tek uses the EHT cover that I have? It's in my box of "miscellaneous metalwork for cutting up and re-purposing" at the moment.

[high_vacuum_house]

Here is the recapped EHT multiplier and cathode/focus supply.

You have to unsolder all of the EHT rectifiers to get at the capacitors underneath. All were leaky to a point there was no EHT voltage at all and even the rectifier filaments would not light. The wire ended pencil valves wire seals are very fragile!!

The blue EHT capacitor on long legs has been tidied up now, I didn't have the correct value so was tacked in temporarily!! it works ok though!! It is the replacement for the black capacitor next to the EHT transformer. Due to its size and location, I cannot get it out without removing several of the heater windings!

You can see the screws for the covers in place including the tall one for the multiplier section, but no covers!!

Christopher Capener

[cmjones01]

Originally Posted by m0cemdave

Does anybody recognise which Tek uses the EHT cover that I have? It's in my box of "miscellaneous metalwork for cutting up and re-purposing" at the moment.

I don't know for certain, but I'd guess at maybe something from the 560 series, or maybe one of the non-plugin scopes. Looks too big to be 453/454 transistor era.

Chris

[Diabolical Artificer]

Does anybody recognise which Tek uses the EHT cover that I have?

No but it may be an early type. AFAIK CRT anode voltages went down over time, the transistor scopes using CRT's with less than 2kv ish, I've not come across a CRT that uses 16kv.

Chris, I might have another spare cover if you need one. I' thought you got rid of all your 500 series scopes, I think I had 3 or four off you a few years back. Those older style of Tek EHT triplers are a nightmare to work on, the later ones used a plastic tray to house the EHT tfmr and caps, much better layout and easier to work on.

Andy.