It needs a wood knob! Making an ebony knob that big without cracking could be quite a challenge.

I will try with wood block pictured. Don't know what wood it is but is's so hard that when I cut it at the carpenter's shop smoke started appearing between the blades and the wood even though I was not pulling hard at the cutter travel. Don't know if I will succeed.

Edited April 9, 201214 yr by Victor Chew

2SC4686 back in stock at Mouser

I did a lifetime buy for me, and they already shipped.

Stock up now, or be sorry.

Just wish I had a working PSU for testing... sigh

The 4686a parts are already isolated, so they don't

Need the ceramic insulators

I know, but it helped make the spacing even

The 4686a parts are already isolated, so they don't

Need the ceramic insulators

I has a sad for your die temps. Plastic parts are already disadvantaged compared to their metal brethren.

no locktite yet (since I'm untested), so I'll just yank them out thanks for letting me know

Thanks for the heads up deepak, finally got mine ordered

Doug what chassis are you using?

Using the vt4c large chassis

And you still need some thermal grease, or the silicon impregnated washers

on the 4686a. Same thing on the ixys part, thermal grease is better for that

and it goes on both sides of the ceramic.

Just a little is all you need. Any more than that makes a mess.

And nothing electrically conductive either, like arctic silver crap.

If its not white, you don't want to use it.

Already have incorporated thermal paste (and yes, it is white). Glad to see I wasnt being over the top by doing so!

edit: in fact, you can see the little tube of it in left of my photo

Edited April 13, 201214 yr by El_Doug

Just for the dummies and to clarify...

The 4686a sand preferably should not be used with al oxide insulators, as the package would be thermally compromised? All that is required is a little thermal paste (white stuff)?

Correct. I have tested the plastic on the 4686a (collector to sheet of metal underneith it, bolted tight) to about 2kv

before breakdown. You can put the aluminum oxide insulator in, but it adds unnecessary thermal resistance

and you don't need the voltage protection.

Thanks Kevin.

El_Doug your build looks great, fingers crossed your psu is up and running soon.

Edited April 13, 201214 yr by johnwmclean

I’ve tested by psu, aiming for a +/-450V output, the result is +/-457V, will this be ok for the 2SA1968’s? I have some 430K’s on hand, that should bring it down to +/- 442V, what do you think...

It will be fine. The 900V rating on the 1968's is conservative as most units surpass it by quite a margin.

Thanks spritzer, that is good to know and saves me tampering.

Well, the second amp powered on without anything blowing up.

On another note, I will be ordering a Khozmo attenuator. Any more issues with reliability?

Edited April 16, 201214 yr by eggil

Congratulations eggil.

I would certainly measure each step on every gang of the Khozmo. Same thing with the Dact's and all other steppers.

Well, the second amp powered on without anything blowing up.

On another note, I will be ordering a Khozmo attenuator. Any more issues with reliability?

let me know if you get an email reply from them. and interested in your comment on "more" issues with reliability

I did get an email from them within 24 hours when asking for information yesterday.

They look very nice and I did not mean to imply anything.

The only thing I know about them is what people have commented here and somewhere else. There are a couple of comments in this thread too.

Edited April 16, 201214 yr by eggil

I did get an email from them within 24 hours when asking for information yesterday.

They look very nice and I did not mean to imply anything.

The only thing I know about them is what people have commented here and somewhere else. There are a couple of comments in this thread too.

Why not use a quad (or 2 ch) TKD pot? Then you aren't left worrying about the long term reliability of an unknown mechanical switch

I think Horio and Cobra Kai have used the Khozmo.

IIRC, Horio used the 10K.

That's is probably the one I'll get.