Tektronix SC504 HV multiplier

[bd139]

Nice job 

[floobydust]

That's good news, there's not much room in the box, even for disc caps from the '70s.
What's the second resistor/part values, so I can update and post a schematic- unless you have a sketch. I have 1.5 Meg in series with the output.
You used a two-part epoxy?

[Doug Brewster]

That's good news, there's not much room in the box, even for disc caps from the '70s.
What's the second resistor/part values, so I can update and post a schematic- unless you have a sketch. I have 1.5 Meg in series with the output.
You used a two-part epoxy?

I had to use 2 resistors simply because I didn't have a 1.5Mohm. They're 1Meg plus 470K. The two part potting compound is made by Robnor; I got the 50 gram pack which would have done three of these multipliers. Dielectric strength is 14.2KV/mm.

I now have another multiplier to do so I'll buy in parts more suitable for the application and I've also ordered some more burrs. Mine are all burned out...

Many thanks for the circuit by the way...

[Doug Brewster]

I should have said in the post above that I've used 10KV 2200pF caps and 12KV (T73) diodes.

[bd139]

Out of interest, where did you source the diodes? I'm doing an HT refurb on a Telequipment D83 at the moment and the current diodes are getting a bit risky to move as they are crumbling.

[Doug Brewster]

Out of interest, where did you source the diodes? I'm doing an HT refurb on a Telequipment D83 at the moment and the current diodes are getting a bit risky to move as they are crumbling.

I "think" I got them out of ebay Germany. I bought and acquired a number of these diodes from about 3 or maybe 4 sources and don't keep good stock control so I don't actually know where I got them. Of course my pc crashed earlier this year and I lost all the emails dealing with the transactions.

[floobydust]

Please review schematic for errors, posted for anyone else repairing Tektronix 152-0634-00 or CMX222 HV multiplier.

HV rectifiers, be careful because most are sized to be under encapsulation, for their PIV rating. Only a few are sized for air.
The 10mm-body parts arc over (in air) around 17kV, and 20mm-body are what you would use in air, like 2CL77 at 20kV.
The ones on eBay/Ali are so low priced, I have been using them with no troubles, although Vf is lower than most (smaller stack).
Inverter microwave oven rectifier diodes i.e. Sanken UX-F5B are huge, for 350mA at 10kV.

edit: forgot part number

[Doug Brewster]

That's great floobydust. I'd suggest a 15KV rating for C3 but physical size may be an issue.

[floobydust]

2,200pF 15kV is 1mm thicker and 2-3mm larger diameter, depending on dielectric Y5T or Y5U but these no-name caps who knows what is used in them.

[Doug Brewster]

Made a couple more of these HV multipliers, one for the failure that occurred earlier in this thread and a spare for my third SC504 which still operates on it's original multiplier. This time I've used a 6.6KV (2200pF) at position C1 and a 15KV (2200pF CERA-MITE Z5U) at C3, leaving C2 at 10KV as before. It was only possible to get a 15KV into the box by reducing the size of C1.

I almost destroyed the box of one of these; got too close to the side with the burr in getting the output HT lead out and thinned the wall so much that it collapsed in my hands. Had to use some temporary walls clamped to the outside so that the potting compound could be poured in and baked and removed them later. One of the walls that was destroyed was that which contained the input and ground terminations. Fortunately it was possible to simply rotate the box 180 degrees, drill some new holes in the sound end of the box for the termination ferrules and another hole in the base for the new position of the output HT lead. All of this meant that I was then installing the components from the opposite side to that which I'd used previously so had to relearn the process; putting these together in such a confined space really is a chinese puzzle..

Anyhow, they're both running fine. Here's a few pics..

[Doug Brewster]

An update. Spent last week in the English Lake District in a caravan and took with me some "toys" as my wife describes them, to avoid going nuts watching TV in the evenings. One of the toys was the scope containing the first HV multiplier I refurbished which contained the marginally rated 10KV caps identified in post #24 of this thread.

The weather was extremely wet and I was running the scope in a TM515 power frame sitting on it's  backside, on a plastic sheet but nevertheless wet ground. It apparently sucked up wet air from the damp ground via the cooling fan and the HV started to arc; I could hear it quite clearly and the trace brightness zoomed up and down several times before I got to the off button. It's been dried out for a few days and is working fine.

Lesson learned but it seems to me to say a lot about modern caps...

[thehobe1]

I am about to take your schooling on replacing/rebuilding a Tek 502 HV 3X multiplier. I am planning to use GE silicone as a potting agent. It seems that this sealant has 450kV/inch, high enough for this application. I really liked your photos of the project and am going to order some small diamond rotary grinders from Amazon to clean up my Tektronix OEM "box" with the components inside. I also have a Tek 485 that seems to have a similar HV problem but with a 6X multiplier so that is my real long term project, the SC502 is practice. Unfortunately, the HV block on the 485 has a beam current output that I'm not quite sure of the circuit inside so I will have to research that before I build that unit. Thanks for any advice you can give me.

[Doug Brewster]

Best advice I can offer is to keep talking to the folks on this forum. Great source of info.

At one point I had six or seven of these SC504 units (bought 5 in a job lot) and put rebuilt multipliers in at least four of the seven. No complaints so far and still have two of them which I use frequently...

[floobydust]

Maybe start a new thread for TEK 485 HV x6 multiplier U1600 152-0509-00?  If it shorts, R1602 smokes. Beam current is monitored with an extra diode/cap.
http://bama.edebris.com/manuals/tek/485

[Jim_W]

I've acquired a Tektronix SC502 and the HV Multiplier is bad.  Before I completely destroy the HV Multiplier with a Dremel tool, I was wondering if  anybody has been able to verify if the posted schematic for Tektronix PN 152-0634-00 is correct?  There was some question about the voltage rating of C3.

Another wiring possibility is that the bottom of C3 connects to the top of C1 instead of ground.  This would be consistent with a 10kV rating for C3, but the ripple filtering would not be as great.

[floobydust]

I had done LT spice sims and the configuration with C3 connecting to top of C1, instead of GND, does not actually work as a tripler...
We know the AC input goes not to one capacitor (i.e. Cockroft Walton), but to a diode and capacitor. The only part not 100% on was the 1.5MEG arc limiter, not that it could really take it unless larger carbon-comp. It's just to protect the diodes. Cockroft Walton also has 1/2 wave ripple when using an odd number of stages.

On that schematic I drew, my sims show:
C1 sees Vpk
C2 sees 2*Vpk
C3 sees 3* Vpk