6n2p-ev question

[77seriesIII]

I have a spare Rev D board and have a slew of 6n2p tubes and would like to try it out. Before I do so I need to make sure I understand the pin out differences.

w/o modding the board and not mounting the novel to the board I think I need to do this:

Solder two wires to holes 4 & 5 on the PC board and solder those wires together to pin 4 on the novel tube socket.

solder wire from novel pin 5 to PC board hole 9.

Novel pin 9 to ground. Do I need a grid stopper resistor and if so what value?

I know folks have tried it in the board, how does it sound?

Thanks

Erick

[EWBrown]

The 6N2P is very close in operating characteristics to 12AX7, (the rp and gm differences are fairly minor, the mu is the same) with the exception of the filament connections being pins 4 and 5 (as with a 6DJ8 or 6CG7). Pin 9 is not used, or it may be an internal shield between the two triode sections.

To modify the Rev D board, the etch connecting pins 4 and 5 must be cut. Otherwise the 6N2P filament will be shorted by the PC board. Also cut the etch (next to the solder pad) for pin 9, and connect pin 9 to a convenient ground on the board (or just leave it open).

Depending on the cut, either pin 4 or pin 5 will be connected to the existing 6.3VAC traces on the board. The other side can then be "stolen" from the cut etch that was previously connected to pin 9, or from the adjacent 12AU7 socket's pin 9. It is imperative to verify your filament voltage connections with a resistance test, using any VOM or DVM, before applying any filament voltage, just in case the wiring ends up as being shorted.

It is actually a lot simpler than it sounds, just be careful and patient.

As the original circuit doesn't have a grid stopper, the 6N2P shouldn't need one, either.

/ed B

[77seriesIII]

Ed,

Thanks for the reply. I was going to pull the socket off the board and wire it separately. I didnt want to sacrifice the board if I didnt like the tube. If I leave it on the board, I should leave the socket attached cut pin 5 and 9 but I have let pin 4 stay active for the heater? I think that is what I understood and makes sense.

In your opinion, is the tube worth it? I got about 10 of them so...need to make something with them.

On the grounding of pin 9, read it over on the diyaudio board, a bit of discussion about the tube building a charge, not all the time, but once it built it would cause all kinds of distortion, too easy to take it to ground and end the issue.

./e

[EWBrown]

I have some of the 6N2Ps as well, though I haven't yet put them into a working amplifier, just run some gm tests on them to see if there was any consistentcy in the batch (yeah, they're "good enough for government work" but not razors' edge matched, either

The actual operating characteristics are slightly different from 12AX7, but the mu is the same (100) and at least in Tube CAD, they are directly interchangeable (except for the filament connections).

I should have mentioned one alternate method, is to flip up the filament pins and just wire them to the 6.3V connections on the PC board. THat way there is no need to hack up the board.

/ed B