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So to elaborate on spritzer's comment, the 6S4A is a single triode tube, the 12AU7 is a dual triode tube.  The 6S4A triode has a much higher max plate voltage (550 volts vs 330 volts) and power dissipation rating (8.5 watts vs 2.75 watts), different filament requirements, they are wired completely differently. their internals look completely different, and neither will work in a circuit designed for the other.  They do plug into the same socket so they must otherwise be completely identical :horsey: .  In summary, they are as alike as Arnold Swarzenegger and the Bobbsey twins.  If your friend can't tell the difference between the two tubes he likely can't tell the difference between Arnie and Bobbsey.

 

thanks a lot, for this i can argue with my friend.

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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

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

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might want to tell your friend to use properly sized heatsinks as well

 

 

 

oops.. this one was the first demo prototype i built.......

 

it seems no problem but i have replaced it to large size.

 

also replaced the chassis.

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i will start.

 

very simple power supply, roughly same as original BH supply at lower power, zener based.

definitely drifts with temperature.

 

resistor based output tube. See JimL posts on current sources.

And the resistors look like 100K which is extremely inadequate, but

match the power level of the tube.

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That's just so many levels of stupid.  :palm:  Was the intended goal of this design to copy the RSA A-10? 

 

I'd love to know the distortion that phase splitter is spitting out.  Too tired to run it in simulation. 

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Overall view looks like PS board at left, unbalanced to balanced board at top and two amp boards.  

 

I'm guessing the unbalanced to balanced board uses a 12AT7 as a long tailed phase splitter with a 2SK170 current source on the tai to improve output balance, with capacitor coupled outputs.

 

A top view of the amp board before assembly would be helpful.  Looks like a 12AT7 driver capacitor coupled to a 12AU7 output tube, also capacitor coupled. Load resistors on the outputs which means a lot of the signal current burned up in the load resistors.  Not an A10 clone - not enough tubes for SRPP.

 

I'm thinking more parts so more complicated than an SRX, but less sophisticated.

 

In terms of potential output power based on combined plate dissipation, 12AU7 < 6CG7 (used in SRM006) < 6SN7GTA (modified SRX) < 6S4A (KGST) < EL34 (BHSE).  The SRM007 uses 6CG7 in parallel so more potential output power than a 6SN7GTA but not as much voltage swing, however the 007 uses load resistors so using good current sources with a 6SN7GTA puts it back on top in terms of available output power.

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And the resistors look like 100K which is extremely inadequate, but

match the power level of the tube.

On the amp board there are two sets of four 12k resistors, which I'm thinking are the plate resistors in series connection to make 48k.  Those resistor values don't make sense as grid resistors and probably not as cathode resistors in parallel either, as the cathode shouldn't need that much power handling, so what else could they be?  Not sure of the values or function of the two large resistors between the red capacitors.  Anyway, if I'm correct, with +/- 300 volt supplies and the tubes biased so that half the voltage is across the plate resistors and half across the tube, that would make the standing current about 6 mA/plate and the tube dissipation about 80% of max.

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I was thinking those other resistors might be the plate resistors, but then what are the ones in between the caps.

 

Anyway with the resistors not lifted off the board, the same thing will happen that has happened to the kingsound amps.

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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 :D

 

Here's the beast in it's intended home:

 

2015-05-03%2014.15.42.jpg?psid=1

 

 

Still need to do the finish and put a respectable knob on it.

 

2015-05-03%2014.16.55.jpg?psid=1

 

 

Here's the back of the amp.  Because of the size I wanted to use a single 5 pin mini xlr.  Had to build a cable as well.  I Put the DAC behind the night table to keep a clean look.

 

2015-05-03%2014.17.52.jpg?psid=1

 

 

I'm just spent the last couple of hours listening and just love it.

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That looks fantastic...and that small footprint.   Gobsmacked.

 

I have to say, my KGST is that cat's arse.  Only wish my damn SR-007A's didn't present a channel imbalance within a week of receiving them new.  Oh well.  The Koss ESP's and a closed set of dynamics I bought recently are holding me over.

 

Can't say enough good things about the KGST design.  I'm no expert, but paired with the 007A's.....oh my.

 

HS

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