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Old 24th April 2012, 01:18 PM   #991
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Looking at the drawing attached to post 989, -ref is nothing more than a label.

Roscoe
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Old 24th April 2012, 02:58 PM   #992
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Quote:
@juanitox did you do your vote ......
no Merkel has done it for us

i like your " brainstorming" for the CCS version, but at last what have done N.P to prefer a Res load to CCS for his bigger Sit AMP ?
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Old 24th April 2012, 04:03 PM   #993
generg is offline generg  Germany
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Quote:
Originally Posted by juanitox View Post
no Merkel has done it for us

i like your " brainstorming" for the CCS version, but at last what have done N.P to prefer a Res load to CCS for his bigger Sit AMP ?

Oh, we have Cohn here, should we send Angela to you..... but will Carla say...?


the brainstorming is simply because SIT-2 was published earlier and I supposed it to be a Mu-follower like J2, so I was fascinated by the idea to drive a Mu with two Semisouth alone without J-Fets. Indeed I succeeded to get it running, but the gain of the two "pentodes" was too high about 25db. Much hum and hissing was the consequence. But the sound was good and then Mike started with the SIT and it has a lower gain so I saw the chance to build a better Mu with less gain......
That is the reason I was fixed a bit on the Mu....
But for sure the resistor solution has the best details and attack at least with the thick film resistors.

I am sure Nelson saw small advantages for the resistor solution and maybe the cap he chooses is a bit more warmish and can compensate a bit the directness of the thick films.
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Old 24th April 2012, 08:16 PM   #994
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something i don"t understand in the Sit 1 pic , i can see the Two white cap for inpout and output coupling, the power supply in the center but what is for the seven big caps near the loading res , additional filtering?
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Old 24th April 2012, 10:18 PM   #995
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I've been staring at those big caps in that picture too. Additional PS filtering, output coupling, slow start, and source R bypass are the options that come to mind.

I want to know how the gate bias voltage is generated and how the slow start is implemented in the SIT1. Knowing this would help sort those caps out.

The gate biasing circuit of the SIT2 prototype isn't obvious in the SIT1. Perhaps they are doing it differently.

The SIT1 has a nice slow turn on (~10 seconds until the bias settles). Nelson accomplished this same thing on the F2 with BIG caps, so I wouldn't be surprised to see brute force used here too.
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Old 25th April 2012, 07:17 PM   #996
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I've never mounted a TO-3 before. Are these two pieces good candidates or are there better choices?

Insulator
Digi-Key - BER166-ND (Manufacturer - HF115AC-0.0055-AC-05)

Socket
Digi-Key - 4601K-ND (Manufacturer - 4601)

Regards,
Dan
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Old 25th April 2012, 07:30 PM   #997
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You're probably better off with mica & grease, but the socket looks fine (or, you could do without a socket)...

Roscoe
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Old 25th April 2012, 07:32 PM   #998
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I picked this up because it was a complete kit.

http://search.digikey.com/scripts/Dk...5K-ND&x=15&y=5

4725K-ND
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Old 26th April 2012, 11:46 AM   #999
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Heatsinks Revisited. I'm wondering if the Wakefield 433K would work.
433K - WAKEFIELD SOLUTIONS - Heat Sink | Newark/element14 Canada

It seems to have similar thermal efficiency to the aforementioned Aavid D180-20.
D180-20 - AAVID THERMALLOY - HEAT SINK, T SLOTS | Newark/element14 Canada

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Dan
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Old 26th April 2012, 05:36 PM   #1000
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If that spec sheet rating means 42C above ambient, then no.

The forced air rating for the 433K is .28C/W, so .84C/W for natural convection sounds feasible, so again, no.

The D180-20 has a natural convection rating of .33C/W according to the catalog.
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