Posted on Saturday, 19th May 2012 by Auw Jimmy

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Please go back here if you haven’t read the first article. On this second part, I’m about to create the potting ingredients to pot my Lundahl choke. I have several experimental ingredients, so some of them might not be exposed in detail as the result is still beyond my imagination.

One of important thing that we have to remember is beware of the chemical and its effect. Some of this chemical could be dangerous if exposed with fire. The solution is to use temperature controlled electric stove or for a ‘poor man’s tools’ – I would prefer a simple double boiler. You can use candles (note the ‘s’, means you need more candles to reach your needed temperature) or you can use gas based stove. FYI, double boiler would be safer (if you can’t get a temperature controlled stove) as the temperature mostly would not exceed 100 degrees Celcius.

My digital infrared thermometer definitely becomes a very handy device here. I can monitor the surface temperature on different side of the pan. Just to make sure it will not exceed my needed range.

After finishing one ingredient, I need to go for the 2nd one. This one is to re-lacquer my Lundahl choke (I don’t know if we do have term ‘re-lacquer’ in English, though). This Shellac is very common used for this purpose. I buy in flakes, so need to crunch them into smaller parts. A coffee grinder should fit the job, but I doubt I can have access to that device without hearing any scream inside the house ;) So, manual job with a hammer should fit the job.

Pour them into my 96% Alcohol. This is a really heavy cut of Shellac. Not quite sure if this really works or not as normally I use 1-2 lbs cut, this is several times higher cut.

Juice is ready! Several days needed to make sure they all blended well. They can have use of shaking and stirring for sure!

Curing test for the Shellac. Nice ‘chocolate’, huh?




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Posted in DIY Audio | Comments (12)

12 Responses to “Potting the Lundahl Choke [Part 2]”

  1. triodethom Says:
    May 19th, 2012 at 21:59

    Potting material from those who do it commercially is mostly sand and tar. Shellac is the more classic classic method . In places like Caly solvents used for shellac can’t be used . Shellac is a very good sealer against moisture in a closed can . Tar or some damping material with sand for mass may prove to be better. I think the major reason for it use commercially is it is very cheap as well as a good damper . The down side is it retains heat so running the choke under rated value is a must. Thanks for your blog always enjoy what you are doing.



  2. Auw Jimmy Says:
    May 19th, 2012 at 22:43

    Hi Triodethom,
    I think most manufacturer will keep their potting material as their own secret, though I believe they would not run away from ‘that’ stuff.
    I would avoid sand and tar, with reason that you have mentioned.
    Some waxes also good, but due to low melting temperature, we’re gonna need some extra stuff like dammar to make it better.
    Well, life is full of choices, isn’t it? :)
    Thanks for reading.



  3. Agus Says:
    May 20th, 2012 at 09:46

    Siang ko,

    Makin aneh aja mainannya.. hehehe…
    Kalau pakai alkohol bukannya nanti ketika sudah kering volume dari ramuannya akan berkurang drastis dan bikin ramuan pengisi jadi crack dan mengkerut?

    Salam :)



  4. Auw Jimmy Says:
    May 20th, 2012 at 10:25

    Siang Pak Agus,
    Kan ga semuanya pake Alkohol Pak. Itu kan hanya ‘sebagian’ he he he.
    Thanks.



  5. triodethom Says:
    May 20th, 2012 at 21:38

    Jimmy that was from the man who sold the second largest lighting ballast maker in the USA . The real secret is there no real secret. You are always fun to read.



  6. Auw Jimmy Says:
    May 20th, 2012 at 22:11

    Hi Triodethom,
    No real secret but still no one will tell you what they are using, right?

    So, personally, I would ‘appreciate’ that as ‘their secret’ even though some of us can guess ‘their secret’. For the sake of curiosity, somebody can just open, break them, burn a bit, and smell or see what’s inside. It’s doesn’t need university graduated in Chemical to find out, I believe. But nobody would be happy if you are digging their backyard, anyway :)

    I’ve known some old guy who insists to use similar material during restoration. Some people will laugh at this old man, ‘Hey, why don’t you just use this commonly available compound? It will work the same with your old one’.

    I’ve also known some commercially manufacturer who switches from tar to other ‘safer’ material. But they just say ‘new enhanced and cleaner potting material’, bla-bla-bla? Secret? Ooo yeah! They can sell extra $$$ from their customer for this ‘upgraded material’, though.

    Also we can easily find ‘modern potting compound’ like from 3M, which produces tar-like finish but with better heat transfer. Clean and nice, no need to smoke your house. But the down side is the cost if you’re potting in large volume. What’s the fun anyway to use this kind of ‘fast food’?

    Well again, for some reason, life is full of choices. And I appreciate that.

    Thanks for coming back. Always nice to have fun and constructive discussion.



  7. triodethom Says:
    May 21st, 2012 at 00:09

    Did Sowter or Lundahl have any thought on potting compounds . I see potted trans from Hammond have gone away from the dist. Ceramic look interesting to me . Cost is high if you want to do any quantity . The reason for sand 1. it cheap 2. When using black epoxy it hidden. 3. Non conductive.



  8. Auw Jimmy Says:
    May 21st, 2012 at 00:57

    Hi Triodethom,
    Like I said, life is full of choices. That’s up to them to pot or not to pot. I believe most of them has their own reason.

    I know (Brian) Sowter and (Per) Lundahl. Have discussed things related with transformer with them and I appreciate their approach. They are great guys and great assets, but again, they have their own choices. Why dont Sowter uses C-core or why dont Lundahl uses EI? I dont think we need to find the reason why…

    I would not comment for Hammond as I believe you know their reason not to pot ;) It’s their ‘common’ secret.

    Yes, again (still), life is full of choices. Sand could be yours. You have reasons for it. I have no concern (and dont care actually). But it’s just not my choice :)

    Thanks.



  9. triodethom Says:
    May 21st, 2012 at 03:09

    Well I agree with you about sand. when are you going to give us a listening test result on this one . By the way just got the Merlin Blencowe book on designing power supplies . It an interesting read for the well informed . This come down to a different view then you have . A real eastern vs western approach to the problem of how to produce a great power supply . The current western approach looses the art of design and the joy of doing a job well . As seen with the meters you have . Regards



  10. Abut Says:
    May 21st, 2012 at 09:40

    Wuihhh Lundahl nya mau di kasih warna coklat he…..he…….



  11. Jimmy Auw Says:
    May 21st, 2012 at 09:58

    Hi Triodethom,
    Listening test should come somewhere later. I got a friend who is using same Choke, but not potted for sure. I can do A-B test directly.

    Merlin definitely a guy with huge knowledge. His website also very nice, informative, and useful. Perhaps you can do the same with your knowledge? :)

    I have no comment about his view inside the book, as there are a lot of viewing angle regarding power supply.

    Thanks.



  12. Jimmy Auw Says:
    May 21st, 2012 at 10:01

    Tenang Bos… yang keliatan ntar kekuningan koq mestinya. Cokelatnya gue uda makan he he he…

    Thanks.



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