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Hi Everyone,

My name's Dom- long time listener first time caller. I've visited Groups.io a few times after searching for old Tek scope info- So I'm glad to finally be interaction with you all!

I have two old Tek scopes- a 535A and a 545B. The 545 is up and running, albeit with a few problems but the 535 is right at the start of the restoration process. It's not in the best condition- I saved it from the scrap heap after its previous owner passed away. I'd hate to see it destroyed.

But one question I'd like to run by the hive mind is about the 5642 rectifier tubes. They're all in pretty poor condition- some of them have actually corroded off their leads. So given I need to replace them anyway perhaps upgrading to a silicone diode could be wise?

I've seen other suggestions online that the NTE-517 of NTE-518 is a good substitute. Has anyone else had luck with this?

I'll attach some photos in my bio- you'll see the Sprague paper oil caps have leaked so they'll have to be replaced too- and the HV section cleaned.

Thanks in advance,

Dom.

Photos attached for reference:

/g/TekScopes/album?id=266461

From the looks of it- five new 5642 tubes will cost me $40 USD including postage, whereas five NTE-518 diodes will be almost exactly the same price.

Dominic:

How about the following as a possible source:

(10) diodes for under US$12.00. Claimed to be equivalent to Tek 152-0408-00.

I have no affiliation with the seller.

Mike D. N4MWP

Dom,

I have used 2CL2H diodes to replace 5642s. The are higher rating than some others that can be used. I got mine off fleabay. If you replace some of the 5642s, the Si diodes would be in the cathode circuit as this has the highest current in the high voltage circuit. The Si diodes work fine and are very fast switching 12kV types.

Mark

Hi Mike,

That's terrific- certainly a lot cheaper than the diodes from Digikey. I hadn't seen that site before and it looks like they have some great stuff! I'll have a browse now and I'll let you know how I go.

Thanks again for your advice- I really appreciate it.

Kind regards,

Dom.

HI Mark,

Thanks for your advice. I can see the one's you're talking about on fleabay- they're certainly a good price. I'll be replacing all five because I'd imagine the corrosion that ate through the legs of the others is probably affecting all of them.

Forgive my ignorance but I'd imagine that removing the 5642 heater loops from the HV transfomer won't have any significant affect on the output of the HV section? I guess it'll need to be recalibrated but can I just install the diodes and remove the heater loops without any further modification?

Thanks again for your advice,

Cheers Dom.

Dom,

The filament windings can be left on or taken off. Check the high voltage when they are replaced. Clean the high voltage area to remove dust, dirt, etc. to eliminate leakage paths, if you have not already cleaned it.

The diodes I mentioned are not the only ones that can be used. If you are in the US and want them faster, use 2CL2 in the search. That will show the series that is currently for sale. There are ones in the states that have a higher voltage and a higher price than the H version. Corroded through wires on 5642s I have seen and replaced them with Si types. The Si replacements will have a lower voltage drop than the 5642s. That may alter the high voltage enough to adjust it. The higher current Si types have lower drop than the low current types of the same voltage. At these voltages, the drop is not a problem, more of information. The prices of these are good. They should not have to be replaced again. A one-time investment. Any spares you will likely use.

I hope you get your scopes working right. I have a fully restored 535A I like to use at times.

Mark

I am sure that substitute does the job well enough. Though - from the historian's point of view I still prefer the 5642 as long as they van be obtained. Tubes are something else than seleniums!
Joe

Since Tektronix did offer the silicon rectifiers as an upgrade, I'd think either would be proper, depending on whether or not you want to be serial number accurate.

As I remember previous discussions, the lack of filament drain from the HV transformer will unload the supply a bit, and should make the parts run a bit cooler.? I do think you should check the HV for proper readings after this.? Tek WIKI may have the instructions for that replacement kit.

Harvey

IIRC, Tek’s silicon upgrade mod kits focused on the Low-Voltage power supply, not the CRT.

Dave Wise

From: [email protected] [mailto:[email protected]] On Behalf Of Harvey White via groups.io
Sent: Tuesday, July 27, 2021 11:09 AM
To: [email protected]
Subject: Re: [TekScopes] 5642 rectifier tubes in a Tek 535: Replace or swap for silicone?

Since Tektronix did offer the silicon rectifiers as an upgrade, I'd
think either would be proper, depending on whether or not you want to be
serial number accurate.

As I remember previous discussions, the lack of filament drain from the
HV transformer will unload the supply a bit, and should make the parts
run a bit cooler. I do think you should check the HV for proper
readings after this. Tek WIKI may have the instructions for that
replacement kit.

Harvey

On 7/27/2021 1:10 PM, Joe wrote:

I am sure that substitute does the job well enough. Though - from the historian's point of view I still prefer the 5642 as long as they van be obtained. Tubes are something else than seleniums!
Joe

I don't know if this helps, but I have uploaded this mod kit instructions that is applicable to the scope

File name:

Tektronix 040-0395-00 mod kit instructions

Thank you, Ken. This mod kit replaces early-production 500-series selenium rectifiers in the LV supply with silicon. There’s nothing for the HV supply; modded scopes continued to use 5642’s.

From: [email protected] [mailto:[email protected]] On Behalf Of Ken Eckert via groups.io
Sent: Tuesday, July 27, 2021 11:44 AM
To: [email protected]
Subject: Re: [TekScopes] 5642 rectifier tubes in a Tek 535: Replace or swap for silicone?

I don't know if this helps, but I have uploaded this mod kit instructions that is applicable to the scope

File name:

Tektronix 040-0395-00 mod kit instructions

Dom,

Diodes are made from many materials, but silicone is not one of them.

a note of correctness: Silicone is a polymer used to make things slippery, as in a lubricant. Some adhesives are also made of silicone compounds. It is also the filling agent for implants used to enhance or replace certain body parts.
Silicon, element 14 on the periodic table, is an element that is plentiful here on Earth, and is used for many things, among them semiconductor devices such as transistors and diodes.

--rick chinn

Well, I am glad someone said it. All day I was wondering about diode implants....

Jeff KruthIn a message dated 7/27/2021 7:19:21 PM Eastern Standard Time, rickc@... writes:?Dom,

Diodes are made from many materials, but silicone is not one of them.

a note of correctness: Silicone is a polymer used to make things slippery, as in a lubricant. Some adhesives are also made of silicone compounds.? It is also the filling agent for implants used to enhance or replace? certain body parts.
Silicon, element 14 on the periodic table, is an element that is plentiful here on Earth, and is used for many things, among them semiconductor devices such as transistors and diodes.

--rick chinn

Ha! Oh dear... I wrote that on my phone so perhaps I can blame autocorrect.... either way it's a good case for proof reading one's work.

Yes I'd imagine silicone valley is in a different part of California... more focused on the front end work ;)

Silicone valley is obviously located in Hollywood.

Harvey

Silicone diode for reference:


The picture doesn't show it, but I added plenty of RTV silicone to the diode too because I had a bit of corona around the rubber boots.

I agree Harvey and Silicon Valley is close to Palo Alto/ Sunnyvale/ Mountain View area.
oops back to the original thread.

(I have a 575 just obtained that is going to need work the only one upon quick look is a 5651 that has its gas missing...zener will not be stable enough under temps.)
..It is currently stored at a friends so i have been looking at the circuits seems to be very similar and I can see silicon diodes should do just fine if the tubes become unobtainable. I would think 100ma more than enough for that application. the 5642 tube has 250ma max.

搁别苍é别

Just wondering: Is it feasible to replace a 5642 with a string of (for example) cheap 1N4007's?
I don't have a need to do this at the moment, but I already have a bunch of them.

Pete

Regular 1n4007s are too slow. UF4007s are fast enough, but it's easiest to just get proper HV rectifiers (which are actually made from strings of series diodes inside).

Ed