Randall RG100ES Question

[JHow]

I know the original poster wants to make his own and I appreciate the challenge in that, but if I might suggest finding an original and just keeping it in playing order might be best .  In kind of kicking myself for not ordering 100 extra 2n5484 back when mouser had them.


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[J M Fahey]

They are still available, just not called the same.
If you check latest datasheets about them, I think that by Fairchild or Vishay, even if they state "not recommended for new designs" meaning they are about to be made obsolete, you'll see a small sidenote stating that they are "sourced from Process 54" or something similar, which I *think* is some internal code referring to that particular die.
They also offer spare unmounted dies of almost anything they make, for hybrid circuit makers.
I *think*  any other similar specs which also states "sourced from Process 54" (or whatever number the 2N5484 is) will be electrically the same, at least within the (wide) tolerance the original ones had.

And, worst case, build one Randall gain stage with a socketed FET and try a few, tghen separate the ones which give reasonable (around 12/16V) on Drains .

[MRMcGovern]

You guys are awesome! Thanks for all of the information thus far. I'm definitely going to do this build, I sort of dove in and started ordering parts figuring a) I'm confident that this forum will provide the support and knowledge needed to get this thing working, and b) I could just find the parts and order them.

I know a) still holds true, b) on the other hand is where I'm starting to struggle. The schematic shows a 2.5A circuit breaker, which I'm assuming needs to be rated for 120vac. I can't find this anywhere! Should I just replace it with a fuse? If so, slow blow or fast acting?

I'm also wondering how to go about finding a chassis. Does anyone have any idea what size the Randall chassis is? From what I've read I believe I should try to find aluminum. And from the looks of this page, and the information in this thread, the chassis itself is the heatsink, with the addition of some aluminum blades screwed to the top. This thread really gave me a better idea of what I've just described. http://gear-monkey.com/forum/showthread.php?t=55

Sorry for the lengthy post, but in short, does anyone have any suggestions on a breaker/fuse and/or a chassis?

[J M Fahey]

Yes, you can use a same value, slow blow fuse.
I *think*  Hammond offers a few "blind" aluminum chassis in a few sizes.
One should fit.
Holes are on you but aluminum is relatively easy to work with at a home workshop.
I should know, I have never usad an iron chassis and make my own in aluminum
Way over 10000 of them by now, probably reaching the 13000 to 15000 mark these days

[Roly]

...on the other hand, I've never been a great fan of using the chassis as the heatsink coz it has so often ended in tears.

The vastly fewer builds than JM that I have done I generally use a steel chassis for strength, and specific heatsinks for that job.  My worry is that the chassis you make may, or may not, have sufficiently low enough thermal resistance.