• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

High voltage and heat sinks

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#22
chrish said:
I had some problem with arcing with a regular bolt and insulator with my HV supply regulator. I used a nylon bolt and no further issue.
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Where did the arcing take place; e.g. through the shoulder washer or from the bolthead to the TO-220 metal flange?

I haven't had arcing occur below 500V but maybe I've been lucky.

For higher voltages I use the TO-247 or TO-3P case devices which have an insulated hole for the mounting bolt. For a regulator circuit these are fine e.g. FQA7N80 or IXGH6N170.

The aluminum oxide pads rock. I haven't checked the breakdown voltage but they are hard to damage. For PC work they need extra clearance for the thickness of the pad itself.

For dissipation under 2-3 watts sometimes the metal chassis itself can be an adequate heat sink.

+1 on the heatsink sandwich, device inside and heatsink outside.

Here's another way. I use a vertical PC mount heatsink as pictured and remove the solder posts. I then drill 2 small holes in the chassis to fasten the heatsink using self tapping screws, and a large 1/2" hole in the center for the device leads to go through the top. I then connect to the device leads underneath using a 3 pin Molex connector. Cheep and cheerful!

Michael
 

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#23
From what I could see from the tracking, and the odd occasion I saw a spark, I am assuming that the arcing was happening between the bolt head and the metal flange of the 220 package. I was getting it on the IRF840 pass device of a MAIDA style regulator. The regulated voltage was 400 volts, so the pass device must have been getting 450 or so, maybe higher for the turn-on spike.

This was causing me a whole lot of problems on my latest amp build (due to my general lack of experience). Took me a while to work out what was going on and come up with a solution that worked.

Chris
 
#24
chrish said:
I had some problem with arcing with a regular bolt and insulator with my HV supply regulator. I used a nylon bolt and no further issue.
Click to expand...

I've had the same issue. Also on a Maida-style regulator. Though, I think it was the LM317 that threw the spark. I traced it down to a burr on the heat sink and a shoulder washer that had a nick in it from being pinched during mounting.

Of course one could use an LM317P (isolated TO220FP package).

~Tom
 
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