Tektronix 2215 Repair - CRT HV Multiplier - Page 1
Forum section: electronics / repair

author: sean0118
author_rank: Frequent Contributor
timestamp: July 30, 2025, 12:36:24 pm
content: Hi all,I rescued this Tek 2215 with a missing HV multiplier module (A10U990 152-0791-00). I don't really know it's history but I heard the multiplier failed and efforts to build a replacement weren't successful.I was going to part it out, but it seems to be in good condition, so I'm starting to think I might look for a replacement multiplier.I could also try to build onelike this. But one problem is I don't have the old multiplier to use as a reference, what type of connection do these have? The CRT on mine still has the HV lead which seems to go to a type of quick connect crimp? Maybe worst case I could cut the lead and solder it to the new HV multiplier directly?https://w140.com/tekwiki/wiki/2215

author: squadchannel
author_rank: Frequent Contributor
timestamp: July 30, 2025, 12:47:18 pm
content: https://www.tekandhpparts.com/?product=152-0791-00-2sphere has it in stock.

author: sean0118
author_rank: Frequent Contributor
timestamp: July 30, 2025, 01:08:07 pm
content: Quote from: squadchannel on July 30, 2025, 12:47:18 pmThanks, that was super fast. That website didn't come up when I searched Google for the part, definitely good to know.It also solves the question I had, "has fast-on tab for attaching HV cable", I guess the connection tab just sticks out of the epoxy?I'm feeling kind of enthusiastic about trying to build one now. It seems it's a common part to fail on the 2215, so might be able to help others.Here's some photos. I have the PSU cover and main enclosure cover, is there anything else missing from the photos? It was in pieces when I got it, I still need to work out where the shield in the last photo attaches:

author: Kean
author_rank: Unknown
timestamp: July 30, 2025, 05:30:29 pm
content: There are some good photos in this thread which show where that shield mounts, and maybe will help identify anything else missing.https://www.eevblog.com/forum/repair/tektronix-2215-scope-repair/

author: sean0118
author_rank: Frequent Contributor
timestamp: August 03, 2025, 06:27:43 am
content: Quote from: Kean on July 30, 2025, 05:30:29 pmThanks, turns out the shield goes over the HV multiplier (I was thinking it was for the mains inlet but couldn't get it to fit)I found a very useful cross reference guide on the Tek Wiki. The 152-0791-00 is only a x2 stage, 4kv to 8kv with a 1Mohm series resistance. Just need to work out how to make the output spade terminal, I assume the original is shrouded?https://w140.com/tekwiki/images/e/e1/Tektronix_Semiconductor_Cross_Reference.pdfedit:Maybe not as straightforwards as I thought, service manual and schematic show it as x4 and +2kV to +8kV. It also needs to generate -2kV, but that's not too hard as long as the input is +2kV and not +4kV.I found some photos here, looks like it does just have a spade / quick connect tab sticking out:https://elettronialtramonto.forumfree.it/?t=79029613

author: tautech
author_rank: Super Contributor
timestamp: August 03, 2025, 08:58:56 am
content: Probably just a quadrupler to take -2kV to 8kV.Follow this thread and build your own:https://www.eevblog.com/forum/repair/tektronix-465/msg651735/#msg651735

author: sean0118
author_rank: Frequent Contributor
timestamp: August 03, 2025, 11:58:34 pm
content: Quote from: tautech on August 03, 2025, 08:58:56 amThe input is +2kV from the stud on the side and it outputs -2kV to the PCB.I'm starting to think that maybe it generates the 8kV from the 4kV differential between the two. Although maybe the internals don't really matter as long as the replacement can supply -2kV and 8kV.

author: floobydust
author_rank: Super Contributor
timestamp: August 04, 2025, 12:48:50 am
content: A good thread on remaking a Tektronix SC504 scope HV multiplier:https://www.eevblog.com/forum/repair/tektronix-sc504-hv-multiplierbut it is atripler, final schematic is Reply #31.Tektronix 152-0791-00, Unitrode CMX554D or Murata MSL8509 - What is needed is a teardown of one, because inside there are surge resistor(s) and we don't know their values.For the 2215, "High-voltage multiplier U990 utilizes the 2-kV winding of Τ940 to generate 8 kV at one output to drive the CRT anode. It also uses an internal half-wave rectifier diode to produce -2 kV for the CRT cathode. The -2 kV supply is filtered by a three-stage low-pass filter..."It looks like that and a quadrupler. But the module is small for all that?edit: oh wait that table gives 1MEG.

author: tautech
author_rank: Super Contributor
timestamp: August 04, 2025, 12:57:25 am
content: Quote from: sean0118 on August 03, 2025, 11:58:34 pmNot really as it's from a transformer whose primary is driven by an oscillator however as you say at one point inside the quadrupler the -2kV is pulled out after a DC restorer diode.Typically this DC restorer diode is on the EHT PCB but in this case Tek chose to fit it inside the quadrupler and bring it out to a terminal....clever or not as if the DC restorer diode fails the complete module must be replaced.As the -2kV EHT suffers more load than the 8kV PDA IMO it's wiser to have the DC restorer diode separate should it fail.....we all know how the M Ohm EHT biasing resistors drift all over the place with age.Xray or depotting it will show how many diode/cap stages there are for you to craft your own replacement.

author: floobydust
author_rank: Super Contributor
timestamp: August 04, 2025, 02:02:42 am
content: Strange, it's the smallest size HV multiplier of them all 1"x1"x1.85" only 47mm height.Draft schematic of the possible innards for everyone to review, it might look like this inside.edit: fixed as Cockroft-Walton

author: sean0118
author_rank: Frequent Contributor
timestamp: August 04, 2025, 10:20:41 am
content: Quote from: floobydust on August 04, 2025, 12:48:50 amThanks, it's a good thread, your point about the voltage ratings in air is a good one. I think the circuit in that thread might be a type of parallel multiplier? It's sort of similar to this one?https://www.voltagemultipliers.com/wp-content/uploads/2018/08/Multiplier-Design-Guideline.pdfAlso interesting is that the tripler in that thread (152-0634-00) is shown as only x1.5 in the cross ref table. I think it's because the table is using pk-pk (6.7kV) input values while Tek sometimes uses pk values in the service manual / schematic? Seems likely that mine does need to be a x4 then. Maybe I'll measure the output of my transformer to check.Quote from: tautech on August 04, 2025, 12:57:25 amOkay good point that it's AC and not +2kV. So if I understand it properly it's just the DC restorer diode inside most likely? The smoothing is done externally with the RC circuits?

author: tautech
author_rank: Super Contributor
timestamp: August 04, 2025, 07:25:47 pm
content: Quote from: sean0118 on August 04, 2025, 10:20:41 amTypically yes.I looked up a couple of old CRO EHT schematics still on file and they typically use a similar setup to this you posted earlier where the -2kV has some RC networks to GND which in the case of this Tek is across the EHT.Follow floobydust draft.....

author: floobydust
author_rank: Super Contributor
timestamp: August 04, 2025, 08:49:01 pm
content: The schematic looked wrong, I was half awake drawing it (FIXED) and then noticed there are different multiplier formats. Villard cascade, Cockcroft–Walton and the "half-wave parallel". The differences are mainly the voltage seen by the capacitors but the latter has reduced output current. I corrected the schematic leaving it basic Cockroft-Walton.C1 sees Vpk, the rest see 2Vpk. So 2kV and 4kV. You can save a tiny amount of room with a smaller C1 but not needed.Looking at the disc capacitors, I thought 2,200pF 6kV Z5U would be OK. Even 1,000pF is not bad for ripple at 30kHz and 2mA.Vishay (Sprague) 564 series like564R60GAD22.That's 13.5mm dia and 6.1mm thick.Very low cost chineseCT81with mystery dielectric are 14.5mm dia and 5mm thick. Y5V is smaller. They are usually at least -20% on tolerance.The diodes all see 2*Vpk. So PIV 4kV.2CL71is rated 8kV 5mA 8*3mm. 2CL71A is 6.5*2.5mm (smaller sized for potting, reduced spacings).Fairly high losses in the 1MEG, 2kV with a 2mA load, around 4W? I must have the wrong guess for the CRT current.I thought the resistor's purpose is to limit output current through the diodes when the CRT crackles. Any tiny arc kills the diodes.I think you could fit all that together?

author: sean0118
author_rank: Frequent Contributor
timestamp: August 08, 2025, 11:25:41 am
content: Quote from: floobydust on August 04, 2025, 08:49:01 pmThanks, looking at Digikey I actually came to the same choice of components. I was going to use the 2CL71A as it's smaller, but you made me think that maybe the larger package size is better because I'll probably attempt without potting initially.Vishay 564R60GAD22 2200PF 6KV Z5UDiotec 2CL71 8000V 0.005ATE RR03J1M0TB 1M OHM 3W Pulse WithstandingI've read lots of conflicting information about the current, I assumed it would be ~10uA, but this thread suggests maybe up to ~1.6mA?https://www.eevblog.com/forum/beginners/how-much-current-does-a-3_-crt-use/It makes sizing the resistor difficult, but I think the RR03 series would be okay, it's 3W at 70C ambient. Another option is the Vishay VR68 series which is 10 kV rated, but only 1W, I might buy a few to see how hot they get. Could maybe put two 510k VR68 in series for 2W?I'm not sure if the RR03 would breakdown or provide protection if the anode does get shorted to the case accidentally etc?Vishay VR68000001004FAC00:https://www.digikey.com.au/en/products/detail/vishay-beyschlag-draloric-bc-components/VR68000001004FAC00/1994729https://www.digikey.com.au/en/products/detail/vishay-beyschlag-draloric-bc-components/VR68000005103JAC00/1994716TE RR03J1M0TB:https://www.digikey.com.au/en/products/detail/te-connectivity-passive-product/RR03J1M0TB/2385221I still need to look for potting compound...

author: jdragoset
author_rank: Frequent Contributor
timestamp: August 08, 2025, 09:08:56 pm
content: 3M Scotchcast resin 4

author: sean0118
author_rank: Frequent Contributor
timestamp: August 09, 2025, 04:34:09 am
content: Quote from: jdragoset on August 08, 2025, 09:08:56 pmThanks, but looks like it needs to be heated? I don't have anything really setup to do that.I found that a silicone potting compound from Chemtools is easily available here.Breakdown voltage of >16kV a mm, should be okay?They also have a "potting box" that's almost the right size, but looks like it'll clash with the other components by about 1mm.https://www.jaycar.com.au/silicone-potting-compound-grey-1-1/p/NA1612https://www.chemtools.com.au/product/our-brands/rapidstick/rapidstick-silicone-potting-compound/https://www.jaycar.com.au/enclosure-potting-box-45x30x25mm-black/p/HB5200edit:This one "might" work:38L x 20W x 20H mmhttps://www.altronics.com.au/p/h0014-38lx20wx20hmm-potting-box/#/

author: quadtech
author_rank: Regular Contributor
timestamp: August 09, 2025, 05:59:11 am
content: You may find this post useful -https://www.linkedin.com/pulse/tek-2215-bringing-analog-oscilloscope-back-from-death-peres

author: sean0118
author_rank: Frequent Contributor
timestamp: August 11, 2025, 09:48:38 am
content: Quote from: quadtech on August 09, 2025, 05:59:11 amThanks, interesting, from the photos it looks like the 20kV capacitors are only 1nF. The PCB is an interesting idea too, but I think I might just wire it all point to point if I can get it to fit.