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i'm on a roll... the kgsshv

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Back up :D


Here's what I broke:





Glad it wasn't more extensive.


I'm going to keep the current where it is for not with the 100 ohm set resistors.  If the heat in the chassis comes down to 120 deg F or less I'll probably keep it here.


I've not put it up on the scope yet, but will get there at some point.

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After 5 years from the time I acquired the PCBs and parts, I finally took advantage of the free time created by the pandemic and completed my KGSSHV.  This is the offboard version with +/-500V supply.

Not sure if we have a KGSS thread but I'll just post this here.  So last year it dawned on me that I built my first KGSS amp 15 years ago and something had to be done to celebrate that.  It started of

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You got lucky there.  :)  I'm chasing ghosts in one HV channel I haver here as it makes a nice sssssshhhhh sound that changes all the time.  All the front end has been replaced and everything checks out fine but still can't find it.  Bloody annoying... 

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Hey guys just an update on the sato denki / 4686A sand group buy I was getting a long while back;


Unfortunately I can't see myself having free time anytime soon to orchestrate the group buy, I really expected to have some time off recently but it just didn't happen.


Please accept my apologies if I had delayed your builds or anything like that, despite my best efforts in trying to convey that the group buy was for stockpiling purposes only.  :-[


I do have 500pcs of 4686A on me sitting around, so if anyone in the US needs a handful and is also up for helping me to distribute them, I could ship the lot to that person. We can work out the details later if anyone does volunteer.


Again, sorry for letting you guys down.

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Any substantial difference in the sound with the current turned back down?


Not substantial but it helps when using the 007's at crazy levels.  That said I'm going to see how the amp is at lower voltage but higher current. 

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LSK389/PMBFJ620 substitute.


The GKSS specifies for this function a 2SK389 double FET, as is used for the Dynalo. For my Dynalo, I substituted it for two BJT, first with the ksc1815 and later, with a different PCB, with the BC550. Both cases worked.


I do not have the ability for soldering the PMBFJ620 and I do not have the LSK389 or the 2SK170. So, I am considering the possibility of using two BJT (with the base at the central pin) in its place: MPSW06 rotated 180º or BC550.


I will appreciate any comments or experience on such a substitution.

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Have anyone used PMBFJ620 with the new KGSShv board?


According data sheet pin 5 is drain(1) and pin 6 is gate(1). When checking the board I get pin 5 routed to gate and pin 6 to drain.


Could it be that there is an error on the board or have I just mixed things up?


I never tested it.  Just compared it with the data sheet but I clearly got it wrong.  Will fix now but it's too late for these boards...  :-[


Sorry about that but the LSK389 is better anyway. 

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You need to use 270v zener if opting for the ksc and ksa.


Also, total of diode strings is 500v for 450vdc and 550v for 500vdc output.


Can someone confirm this? I've been following the PCB and I see each rail's diode string as 3x150V.

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I'm getting some weird behavior out of the latching switch on the front of my kgsshv. I noticed the LED is dimmer than it should be and decided to do a quick check with the DMM to see what's going on. Apparently I'm getting +9V/-15V (relative to star ground) instead of +12V/-12V. Really not sure what to blame here, as the switch LED crapping out on me happened once before. At least it still 'works', for now...

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What do you mean +/-12V?  You should just put the +15V line to the + pole through a dropping resistor (I use 300ohm) and the - is connected to ground.  Two switches dieing is not normal as I've used some 50 switches and no issues. 

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I milled the bottom panel out of wood to make sure everything fits and there is no hum.

so far so good. Still need to get it on the scope.

here's some shots...




the back plates will be powder coated to match the heat sinks.

Edited by Kerry
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