HV cap replacement need advice. (Valhalla 2701C) - Page 1
Forum section: electronics / repair

author: LainisLain
author_rank: Contributor
timestamp: June 18, 2018, 12:09:17 pm
content: So I repaired my Valhalla 2701C voltage standard but need some help finding a replacement part. A large film cap was damaged possibly by a soldering iron at some point. The part is an IMB 0.22uf 1500V 20%. (see picture) Digikey is my preferred parts seller. I've found a few higher voltage caps that may work but none are 20%. I assume a 2kV rated cap at 10% would be an appropriate replacement.There are only a few with a minimum purchase of one.https://www.digikey.com/product-detail/en/cornell-dubilier-electronics-cde/940C20P22K-F/338-1177-ND/809470https://www.digikey.com/product-detail/en/illinois-capacitor/224PPA202K/1572-1089-ND/5344019https://www.digikey.com/product-detail/en/kemet/C4CAWUD3220AA1J/399-11777-ND/5177267They're all around the same price. Can anyone recommend one of these or better yet does anyone have a source for an original replacement?Any help is appreciated.

author: lowimpedance
author_rank: Super Contributor
timestamp: June 18, 2018, 12:52:15 pm
content: The original is listed as a Mylar type in the parts list, I would be surprised if any original supply other than Valhalla themselves would be readily found.But any suitably rated and physically compatible film capacitor will work fine here. All those linked are the same material and close to the same physical size so...Perhaps the Illinois ! .

author: floobydust
author_rank: Super Contributor
timestamp: June 18, 2018, 06:17:43 pm
content: Those three all look like fine replacements. The CDE part is smaller and what I would prefer, rated 60khrs life.I would ensure spotless soldering afterwards, use a q-tip and IPA to clean up flux.

author: LainisLain
author_rank: Contributor
timestamp: June 19, 2018, 12:09:56 am
content: Great! I'll order the Illinois. I'll post back when its finished. Also can someone recommend a replacement for R48 precision resistor on the Valhalla 2107C schematic. Its suppose to be a 68.3k ohm for the HV feedback. I had to stack resistors to get close. Any suggestions for that?I probably should have started the repair of my 2701C on this thread but oh well.The details on the repair are here.https://www.eevblog.com/forum/metrology/valhalla-2701c-(kinda-working!)/

author: lowimpedance
author_rank: Super Contributor
timestamp: June 21, 2018, 01:11:25 am
content: Quote from: LainisLain on June 19, 2018, 12:09:56 amUnfortunately This resistor is part of a matched set which means without knowing what the characteristics they selected for the set (R32,38A&B,R41,A,B,and R48) it will be impossible to match properly. Most likely temperature co-efficient and drift rate/direction were the most important then tolerance. All made as a set for Valhalla, I think Edwin Pettis mentioned at one time he made resistor sets for Valhalla so maybe drop him a PM with the question and he might give you the most appropriate answer.

author: LainisLain
author_rank: Contributor
timestamp: June 22, 2018, 02:05:01 am
content: Is Edwin Pettis a member on the forum? I can't seem to find that name.

author: Vgkid
author_rank: Super Contributor
timestamp: June 22, 2018, 04:20:55 am
content: Quote from: LainisLain on June 22, 2018, 02:05:01 amHere is his account page.https://www.eevblog.com/forum/profile/?u=96921