ktg-1 preamp with 6n2p tubes

[carlozsulca]

I am a big fan of tame impala, especially his first album so I investigated how to get to that tone that he arrives in several of his songs and I found the preamp that he uses, the KTG-1, but the tubes that are used there, They are the 12ax7 that in my country are very expensive, so I opted for the 6n2p tubes, which from what I read is very similar and the best thing is that it is very cheap, but they make a modification on pins 4 and 5, but the modifications I found It is when they have a transformer output and in the preamp they use + 12v DC and I would like to know how to make the modification for this case, thanks in advance, I leave it a schematic that I found on the internet

-https://drive.google.com/file/d/0B1m2UbXzVONQU1hMeGU1bTBvclE/view?usp=sharing

[Marcos - Munky]

I use the 6N2Ps a lot. Nice and cheap tube. They're almost pin to pin replacement for the 12AX7, but for the heaters.

The 12AX7 have two heaters, one from pin 4 to pin 9 and the other for pin 5 to pin 9. Each one needs 6.3V 150mA, and both are connected to pin 9. So you have two choices:
1- wire them in parallel. So you connect pins 4 and 5 together, and feed pins 4+5 and pin 9 with 6.3V 300mA.
2- wire them in series. Since both are already connected on pin 9, you connect the other two ends (pins 4 and 5) to  a 12.6V power supply and leave pin 9 disconnected (that's what's happening on this schematic).

On the other hand, the 6N2P have two heaters but they're hard-wired in parallel. You can't connect them in series. One end is connected to pin 4 and the other end is connected to pin 5, and pin 9 have no connection. So your only choice is to feed the heaters on pins 4 and 5 with a 6.3V 375mA.

So, in order to use the 6N2P instead of the 12AX7, you have to change the heater power supply and that's it. If the circuit calls for pins 4+5 and pin 9 @ 6.3V, change it for pins 4 and 5 @ 6.3V with pin 9 disconnected. If the circuit calls for pins 4 and 5 @ 12.6V with pin 9 disconnected, just use 6.3V instead of 12.6V.

Now, I don't know how exact are you going to power your circuit. If you're going for the original power supply, you can just wire the heaters of both tubes in series and keep the 12V power supply. That means you connect pin 4 of tube A to FIL-1, pin 5 of tube A to pin 4 of tube B and pin 5 of tube B to FIL-2. There are other ways to do it, but this one woudn't need any change on the power supply.