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Here is what I've been doing for the last day or so when time allowed... 

 

KMFbD0T.jpg

 

This one has the tubes mounted on top of the board to make building and testing far easier.  This version uses the old KGSSHV transistors and works with both the fancy teflon tube sockets and the standard ceramic/plastic stuff.  This gives the added benefit of extra holes to cool the tubes.  Boards are 4.7" x 4.7" and as soon as we are happy I'll order some prototypes. 

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Thanks to the NYC Spring Meet yesterday, I was motivated to finish casing up my KGST.  I'm very happy with the result.  The chassis is 7" x 12.8". Perfect for my night table   Here's the beast in i

After almost three and a half months, the KGST is finally in operation, and is sounding great. Thanks to all who have responded to my questions and given guidance. I am really surprised at  how good t

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Very nice, a tiny footprint. Are the new kgsshv substitutions (mpsw*) valid for each of the older transistors? I think I'm running a bit low on those but I have the 06/56 from my krell purchases.

 

Will there be any problems with the film caps being that close to the tube glass? I had reservations about mounting components on the same side as the tubes in the megatron, but I don't actually know if the temps make a difference.

Edited by nopants
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Will there be any problems with the film caps being that close to the tube glass? I had reservations about mounting components on the same side as the tubes in the megatron, but I don't actually know if the temps make a difference.

 

While the tubes will get hot it's above the caps so they won't see too much heat.  Electrolytic caps are rated to 85-105°C but film caps can take way more than that. 

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No board run coming from us but any of you are free to organize one. 

 

it almost looks like you can cut this board in half and stack output stage on top of the front end

 

There would be a lot of wires running between the boards but yeah, it would be possible.  Also, it isn't 100% clear from the pic but next to the heater connector there is a hole in the board to pass the wires through. 

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it seems like a neat way to go if you wanted to easily swap output stages. I've seen it used in a couple places for both amps and dacs. I think they use jumper pins to make that connection though.

might be cheaper to make board runs that way too if it's now 2.5 x 5, but someone else would know better than me.

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oh I meant from a future project perspective, if you wanted to reuse this board work for the front end. I think work is starting to get to me, I keep trying to identify and reuse IP blocks  :-[

 

Just thinking out loud, don't mind me

 

Quick question about the servo though, what's the lead spacing for the wima cap? Shouldn't need more than a 25V rating right?

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Pretty much any film cap would work but it's that big as the cheapest caps are often 250V or so and also much more common.  This was just lifted wholesale from the KGSSHV board. 

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Of course, how did I forget. :palm: Interested to see how the KGST compares to the KGBH, hoping for my wallet's sake that it's close enough. Frankly I have almost exclusively used OEM earbuds straight out of my phone/laptop the past few years, so pretty much anything would be an improvement.

 

Edit: Only difference I see are the 100 ohm input resistors and the servo is connected to the bases of the A970s instead of the 1486s? What else am I missing?

Edited by mypasswordis
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So I've been having some fun with this design.  I've gone ahead and shrunk this thing way down.  Each channel is 2" x 4.5".  I've used some really small SMD parts so not for the faint of heart.

 

Here's the boards:

 

mbtq.jpg

 

 

If you look at the bottom of the board (left center: R4 - U1) I've designed a servo based on the T2 style with an a twist since it needed to push/pull in the opposite direction.  Q1 & Q5 are really small.  Very proud I could solder them.

 

igpo.jpg

 

 

Here's some shots of the amp up and running.  The PS is in the style of the KGSShv PS.  It was an early prototype.  I've got it set to +/-400V.  I added a +/-15V with the transformer mounted to it.  Nice and small and allowed me to use the Antek stock transformer.

 

kxuj.jpg

 

The servo starts the amp at +3V and within 5 minutes has it down to less than 0.1V (see above).  It stays nice and tight within about 0.02V once it settles.

 

 

rfsk.jpg

 

 

7u5y.jpg

 

rd50.jpg

 

 

I've had it on the scope.  Very flat response from 10 - 70KHz (which is all I bothered measuring).

 

oob4.jpg

 

 

I had a chance to listen to the one channel.  So far so good.  Dead quiet and the sound seems to be there.  Need the other channel to really tell.

 

All in all I'm very happy.  No explosions and it does what I wanted.  I'm going to try to build this into a 7" x 12" x 2" chassis.  We'll see.

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