6DN7's

[TurbOSquiD77]

Are matched 6DN7 pairs hard to come by? Having a little more trouble finding a good 6DN7 pair than with other tubes.

-T

[mcandmar]

6DN7's are getting hard to come by.  I wouldn't stress about actual test measurements and matching, just find two matching tubes of the same brand.   Ideally something like this where the seller has a few from the same age/stock. http://www.ebay.co.uk/itm/401260903932

p.s. Just found these http://www.ebay.co.uk/itm/351999477381 nicely matched too looking at the writing on the box's.

[TurbOSquiD77]

Thanks mcandmar 

Those should be here in a couple weeks.
6BL7GTA - There are some nice matched pairs, but I don't think I can run those without modification due to higher current?
The link is crazy long - search "Matched pair of GE 6BL7GTA tubes NOS NIB Röhre Valvola Valve Lampe 6BL7GT 6BL7" on Ebay.

http://www.radiomuseum.org/tubes/tube_6bl7gta.html
http://www.radiomuseum.org/tubes/tube_6dn7.html

-T

[TurbOSquiD77]

I seem to have forgotten that the S.E.X. 3.0 6FJ7 utilizes a Compactron 12 pin socket, and the 6DN7 is octal 
Just too much excitement from how well the build went.
Would a pin conversion to octal be possible without much trouble?

-T

[Doc B.]

Would a pin conversion to octal be possible without much trouble?

I would guess that if you have to ask how to do it, it might be a bit too advanced to tackle. Knowing what each pin is and what it does is essential to getting the conversion right. At the very least, having the knowledge to look up the pinouts online would be a prerequisite.

[TurbOSquiD77]

I'll start now 
Might a manual comparison from 2.1/3.0 be of benefit to me? I'm a visual learner, and also non-visual if instructions are given, but in this case I'm going to try and tackle this without instructions, and post my findings.... and come very prepared to be very incorrect. I believe I could do this myself as long as it does not require modification to the overall circuit, and only rewiring for the octal pinout. 

[Chris65]

The question would be - why? They are the same tube in a different bottle.
You could on-sell the 6DN7's for no loss & buy yourself probably half a dozen 6FJ7's.

[johnsonad]

You could also purchase a set of converters off of ebay if you really wanted to.  This would allow you to use both types of tubes.

If you heart is set on the 6DN7 only, you need the tube data sheets from both tubes and swap the wires.  This easy easy enough to do.

[Chris65]

You could also purchase a set of converters off of ebay if you really wanted to.  This would allow you to use both types of tubes.

That would still entail changing the amp sockets to the octal variety, as there are no bases on Compactron tubes.
Then you could use Compactron to octal adapters as mcandmar has done.

[TurbOSquiD77]

Here's what I've found. Critique away! Please?

edit: I'd like to provide the .pdf's I referenced as courtesy to those who wish to review my findings.
https://frank.pocnet.net/sheets/093/6/6FJ7.pdf
https://frank.pocnet.net/sheets/093/6/6DN7.pdf

6FJ7                      6DN7
Pin 1     -Heater Neg-       Pin 8
Pin 2          -No-
Pin 3     -Grid Section 2-   Pin 1
Pin 4          -No-
Pin 5     -Plate Section 2-  Pin 2
Pin 6          -No-
Pin 7     -Cathode Sec. 2-  Pin 3
Pin 8          -No-
Pin 9     -Cathode Sec. 1-  Pin 6
Pin 10   -Grid Sec. 1-        Pin 4
Pin 11   -Plate Sec. 1-       Pin 5
Pin 12   -Heater Pos-         Pin 7

The only hiccup I found was the resistor on pins 8/10 - I could keep one end of the resistor on pin 4 of the 6DN7, and attach the the other end to a solder post I would mount (I have single tag boards), and wire to the potentiometer. So this is why that mysterious hole is there!!! Maybe. I'm on to you, JHPJPBDOC.... 

Other than this, would it be a direct swap, check voltages, and fire away? Hopefully no fire. Just glow.


I do like the way they look, and everyone is crazy about coinbase 6dn7's so I thought I'd pick some up. That's about it, lol. Also, it would just be a fun experience to figure something out and accomplish a conversion like this - in honor of the 6DN7 who once ruled over all S.E.X.. I didn't know that when changing pinouts all you need to do is reconnect to the new pin. I thought a circuit redesign would be in order or something. Learning something new every day here.

Thanks for the input  Maybe an adapter project for the 6FJ7 would be next.

[Paul Joppa]

Two points:

1) Be sure you know which is triode 1 and which is triode 2. The first 6DN7 amp, built (by Dave Dintenfass) at a VALVE meeting in the mid-nineties, actually crossed them up. These tubes are tough, since the small triode (rated 1.0 watt dissipation) was running at about 6 watts, and sounded fine. But it would not have lasted very long!

2) 6DN7s are used in a few audio applications, and the supply has been picked over fairly intensely. Nobody uses the 6FJ7 other that those still using 50-year-old tube color televisions - not a large customer base! So you can more easily find a good NOS example.

[Doc B.]

Did any of you guys think to compare the socket hole sizes and mounting screw spacing?

[TurbOSquiD77]

Thank you PJ. I like how the first was built at a meeting - kind of cool if you ask me.

Yes Doc! Just haven't actually measured quite yet, but will do! Thank you for reminding. But really, what's that extra hole for? I can only guess! Awaits the mods

[mcandmar]

The compactron to octal converters i made were straight forward because you could source new octal base's to build them into.  Doing it the other way around would be a little more tricky.  Honestly its not worth the effort, 6FJ7's are easier to source.  Which is precisely the reason i made my converters in the first place.

http://bottlehead.com/smf/index.php?topic=5811.0

[johnsonad]

Did any of you guys think to compare the socket hole sizes and mounting screw spacing?

That's what drill presses are for Dan! If you don't have the right tube, make a hole for the one you want 😜