Krell KSA 100mkII Clone

[jacco vermeulen]

Originally posted by AndrewT
try cutting the silly legs off

Now that is truly funny, your sense of humor is spectacularly improving, Mr T.

Although the 2.8 W/C.m number of Duralco compound looks attractive, the 3-5 mills thickness is not if compared to mica and goop. I love epoxy, have used it since 1985 for everything from boatbuilding to potting toroids with thermal epoxy resin, but for semiconductor thermal transfer they'll have to do better.

The legs of TO3s having to go through the heatsink is a downside, but other than that they're still the superior package type imo. Fortunately there's a 2-bolt Jappon alternative.
Covering something that needs cooling with plastic on the top has little rationale, where's the full metal TO247 ? I sometimes miss the 2955/3055 and Hitachi TO3 days, the spreading of TO3 leads is so much nicer than the tight legging of flatpacks. Still think an output stage with TO3s and Al2O3 insulators is a sight for sore eyes, and still waiting for Magura to post some pics of his TO3 output stage with the TO3 aluminium oxyde insulators i sent him. I like drilling and tapping though, my dad paid me $0.50/hr for that when i was 8.
Scrooge alert !
I've heard a rumor that packages that can be heatsinked on both sides do exist.

(I had a 3020, first number that sprung to mind, find the NAD front looks very attractive up till today. And still a budget audiophile product IMB)

[Mark A. Gulbrandsen]

I've posted the zobel values twice on this thread so far: 100nF and 5R6.

I know.... looked but cold not find it. This thread is getting larger every day! It is now posted in the WIKI.....

Mark

[AndrewT]

Hi,
this thread is small beer compared to the Grand Daddy!

Let's see in a year's time if the Mods threaten to chop it off as well.

[jacco vermeulen]

Mmm,

Me thinks they did that after some renegades came up with KSA100 plans. They ? Something Pink, i think.

Second thought :
The MJ15024/25 series was a giant leap forwards, at a time when a lot of Rod Elliots were (still) using MJ2955 TO3s. Take a look at a 2N3055 datasheet and compare that shocking one with the ones of Motorola MJ150** TO3s.

Compared to MJ15003/4, OnSemi's MJLs are just about the same evolutionary step size to perfection as the MJ15s were from Rod Elliot's relics from the graveyard.

Still, 20 years later and not a month goes by without some smuck anouncing he's about to make an amplifier with RCA TO3s.

[AndrewT]

Originally posted by jacco vermeulen
Me thinks they did that after some renegades came up with KSA100 plans. They ? Something Pink, i think.

more to do with some excuse about screwing up the database when someone did a search. Seems their puny computer could not cope with VERY long threads AND searching. I believe the ksa50 thread is being held open pending some milestone.

Seems a shame I cannot contribute much to the 50 thread now that I am transferring my allegiance to the 100. Besides, I never built the 50! But I'll do what I can to give the Mods some work.

[acenovelty]

Sorry to confuse the issue, the 3-5 mils is not the thickness required for a bond. That's the amount that needs to squeeze out at the edge for lateral bond to the substrate. Some folks are known to use it like silicon seal around a bathtub by using the finger to smooth it to the edge.
A number of other makers of this space age stuff make even better temperature/non conductive/electrical conductive/ceramic filled and on and on types. You can even find the type that's used on our space shuttle. But the price...............?
Don't personally mind drilling the holes for TO3 since my jig works so well with the drill press.

HTH
Regards

[Mark A. Gulbrandsen]

Don't personally mind drilling the holes for TO3 since my jig works so well with the drill press.

Thats the ONLY way to drill a bunch of TO-3 locations accurately! And if one uses drill bushings to make the jig up it can be kept very accurate as the bushings are easily replaced when any wear becomes evident.

Mark

[acenovelty]

"drill bushings", now that make my little contraption sound absolutely crude. Maybe you'd be willing to elaborate on your method a bit more.
Always looking to learn a better way.

regards

[Mark A. Gulbrandsen]

Drill bushings are hardened steel and solid carbide drill bushings of all sizes used in tooling jigs. They are replacable as they wear to maintain high tolerances in a production type jig. Carr Lane makes excellent bushings.

Carr Lane

[acenovelty]

And according to the Carr Lane definition, what I have is a fixture, not a jig. And by comparison, somewhat crude tho useful.