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SUPPORT FORUMS FOR ZKITS >> ZKIT 1 Support forum >> Pin 1 or 6 on output stage for the cap?
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Message started by svartemarten on 12/30/25 at 13:34:05

Title: Pin 1 or 6 on output stage for the cap?
Post by svartemarten on 12/30/25 at 13:34:05
Hi,
I’m in the middle of building a ZKIT1 and also trying to really understand what’s going on in the circuit as I go.

Looking at the ZKIT1 schematic (Last Rev 8 - 2025)
I noticed the 0.1 µF cap in the output stage is shown between pin 1 and pin 3 of the output tube socket.

On the ZKIT1 PCB though, that same cap is connected between pin 6 (G2) and pin 3 (cathode), which makes sense for the 6P15P-EV.

Am I right in thinking the pin-1 reference in the schematic is just a holdover from earlier point-to-point builds where pin 1 was used as a tie point, and that electrically it’s always meant to be G2 to cathode, as the PCB shows?

Just checking so I’m understanding things correctly — part of the fun of this kit for me is learning why things are done, not just where to solder them 🙂

Thanks,
/Mårten

Title: Re: Pin 1 or 6 on output stage for the cap?
Post by MM on 12/31/25 at 02:56:10
Hi Marten. I’ll take a stab at this from memory. I recall the Hazen mod tightens the control of the electron stream through the tube by using otherwise unused pins. Pin 3 is the cathode to ground and both pins 1 and 6 are unused. My recollection is that it makes no difference whether the 0.1 cap goes across pins 1 and 3 or pins 3 and 6. Perhaps Steve has found over the years that one does sound better or makes more sense from the layout standpoint, but either configuration will work as intended. Happy New Year.

Title: Re: Pin 1 or 6 on output stage for the cap?
Post by svartemarten on 12/31/25 at 16:22:03
Hi MM,
Yes thanks for answering, did some reading up to and the 6P15P aka SV83 tubes do seems to have pin 1 and 6 internally connected
eg. sv83-sed1997.pdf
So from that point connecting the 0.1 µF cap to either pin 1 or 6 does not matter.

Just need to read up on any compatibility issues if swapping in an EL84, but think Steve have already thought of that..

Happy new years

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