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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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I can do a version of the board for 9ra6 if you want

 

but an adapter should be easy, the plate and the filament are the same pins

the cathode and the grid each move down a one pin

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9RA6 version would be nice, I was planning on mounting sockets to the chassis and redoing the pins to the board with some air wiring. I bought some tube socket adapters but the way they were wired inside didn't allow for easy rewiring of the pins.

 

Also thinking about doing the DN25* cascade + 10m90s on offboard sinks

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Take it easy mypasswordis - you like the recording, we get that. 

 

You are not "we" and you may never be "we" as long as you keep lecturing and trying to impress.  Please just stop trying so hard.

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other than the fact that i don't have any.

 

two versions of the 6ra6 board

 

http://gilmore.chem.northwestern.edu/kgst6ra6.jpg

 

http://gilmore.chem.northwestern.edu/kgst6ra6cascode.jpg

 

and cascode version of 6s4

 

http://gilmore.chem.northwestern.edu/kgst6s4cascode.jpg

 

someone please check for errors

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anyone find a 6ra6 or 9ra6 datasheet in english, or at least can tell

if the pins are bottom view or top view?

Sorry, using my Chinese combined with long-forgotten and very limited Japanese, I was not able to find out if the pinout on the datasheet Laowei attached was bottom or top view. All I can say is that the datasheet did not state one way or the other.

I did find another 6ra6 pinout diagram which looks exactly the same but with "T7C" text below it. Not sure if this means anything. I could not find any information relates to "T7C".

FWIW, couple of Japanese sites on tube history state that the 6ra6 was created as an "improvement" or "alteration" of the 6s4a tube.

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  • 2 weeks later...

I've been playing with the servo in my KGST build.  I had a couple of problems. 

 

First, at very high volumes, the servo would fail.  I fixed that by moving away from the LT-1021-10 which requires about 1.3mA to run properly.  I moved over to the LM4040-10 which wants about 150uA.  I set it just a bit higher at 170uA.  Problem solved :)

 

Second, I have a small oscillation of about 100mV around 6.7MHz.  This one has been a bit trickier for me.  I figured I'd post the schematic here.  This schematic has the updated cascaded current source, which is currently not on my board.  The model runs fine.

 

The schematic uses different values for the sand, but they are closely matched to the actual parts used.  Here's where I'm at:

 

KGST-CCS-Servo.gif?psid=1

 

The way it works is that I built a rough op amp (similar to the T2 batteries) which functions as an error amp to hold the input to Q1 at 10V (voltage divider via R9, R10, R13, R14 against R11) same as the input at Q2.  It uses Q3/Q4 (I've used a single Darlington transistor) to create the proper current (about 20mA) to hold the output at 0V.  This is similar in principle to the T2 servo, but need to push/pull in the opposite direction (why I used the error op amp approach).

 

It works great (barring the oscillation) and holds the output within a volt or so from cold to fully warmed up.  It is a simple average of the +/- legs.  Since the oscillation is common mode, outside the audible range and relatively small, I can't hear it. 

 

Any thoughts would be appreciated.

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Neat, I like discrete servos a lot! I'd try injecting on the balance current sources as well. I used this differential discrete servo in a single stage pentode amp, which sensed the plate voltage and injected on the screen grid. It could get both plates within 10 or so uV, if I recall.

 

post-3944-0-02036500-1429588425_thumb.pn

 

The output needs to be loaded with big resistors (this one worked into 150K). Quiescent output voltage is defined by the tail CCS current minus the second CCS's current (which biases the LM4040), divided by two. Current is shifted from one side of the long tail pair to the other as a DC unbalance appears on the input nodes, until the voltage unbalance is nulled. Could work well as a high impedance reference for the input stage's current sources. It might also work on the plate CCSs if enhancement mode mosfets were used to load the plate- not sure how well it works with depletion mode devices.

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Good news!  I fixed the oscillation on the servo as well.  I simply added a 220pF cap across the base/collector of Q3.

 

@pretentiousfood - Looks interesting.  I was thinking about doing something against the input stage.  Not a lot of current and only about 15V.  I'm going to take a look at what you've posted.  Thanks.

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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.

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but but

 

Mikhail said that a 6sn7 and a we421 were identical.

and 6j6a and 5844...

And he consistently shoved all of them into the same socket to prove it.

(with adapters)

and god only knows how many other tubes.

 

and 3d21 In place of 6ca7...

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Hey, does that mean you could connect the source to the output and the load to the input.  ?   :laugh:

 

Would that be called reverse engineering...?      :dance:

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but but

 

Mikhail said that a 6sn7 and a we421 were identical.

and 6j6a and 5844...

And he consistently shoved all of them into the same socket to prove it.

(with adapters)

and god only knows how many other tubes.

 

and 3d21 In place of 6ca7...

Wow.

 

I could call Mikhail a clueless fucking idiot

.

.

.

.

but I'd hate to insult the clueless fucking idiots out there.

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