Puzzling problem with 6SN7 adapter

[corndog71]

Have any of you considered installing an Octal socket? Not hard to do.

If I was considering the 6SN7, and I would. That's what I would do. Give it a fair chance.

We can help...John

No kidding.  I would've changed the socket if I were going to test 30 tubes.

[w0lfd0g]

Have any of you considered installing an Octal socket? Not hard to do.

If I was considering the 6SN7, and I would. That's what I would do. Give it a fair chance.

We can help...John

No kidding.  I would've changed the socket if I were going to test 30 tubes.

Hah - Didn't buy the tubes to test the Crack.  Had the tubes anyway.  Thanks for your suggestion though.

[adamct]

Adapter #4 was the worst of them all in terms of aesthetics (ugly as sin), build quality and usability. It took me about 40minutes just to get one of my 6SN7s into the adapter, because either the holes are slightly too small, or the pins are too tight.

Once I got the 6SN7 inserted far enough, I plugged it into my Crack. Same problem as with the others. Four adapters, and far too much money and frustration later, I'm done. I have plenty of 12AU7s and related variants I can use in the Crack, and I love the way they sound, so I don't even know why I went down this 6SN7 detour. I'll save my 6SN7s for my other amps.

Yes, I know that putting in an octal socket would be fairly easy, but its just not worth the effort to me. I'll stick with the stock socket and 12AU7s. Now I just need to spend another hour or so trying to get my 6SN7 out of that #%^

[Paul Birkeland]

You can heat the driver tube with a DC supply, and your socket noise issues should go away.

-PB

[captouch]

So no one has found an adaptor to use 6SN7's in the 12AU7 socket with no added hum/noise, huh? 

If anyone has, a link would be appreciated.

[dubiousmike]

Some folks do claim that they have noise-free 6sn7 adapters, but my experience has been the same as Adam's.  Granted, I gave up after two failed attempts. 

My second adapter (from lowther), was way better than the first but still noisy enough that my ears felt considerable relief when I switched back to a 12au7.

It may also be that the frequency of the noise is a lot more audible to those of us who primarily use our cracks with hd800's.  When I have a chance, I'll bust out the better of my adapters again and try it with my hd650's.  Their polite trebles may well serve to mask most of the noise.

[captouch]

Thanks Mike.  I have Hd650's and may have a chance to get some 6SN7's for cheap, but I'd prefer not to spend the $15-20 on the adaptor if it's just going to be noisy.

[Grainger49]

It sounds like that if you like the 6SN7 over the 12AU7 you should put in an octal socket and convert.  There are others who have done this and have had no noise problem.  After all, all wiring is under the chassis plate and soldered.

Then maybe a 6SN7 to 12AU7 adapter will be quieter.

[Paul Birkeland]

I'll repeat (for about the 3rd or 4th time) that heating the driver tube with DC will eliminate the noise issue of these adapters, and can be done very inexpensively.

[dubiousmike]

PB - that was my original understanding, but in response to one of my posts in the crack thread on headfi (as "skeptic"), I understood Doc as saying that ac shouldn't really be an issue for purposes of using adapters.  (see posts 1532-1533 https://www.head-fi.org/t/476650/crack-bottlehead-otl/1530_30#post_9222640 )

Have you guys had a chance to do any in house testing on this?  If so, it would be great if someone would post a dispositive conclusion on HF to end any remaining confusion on this point.

[Paul Birkeland]

I don't think we have any adapters in the house.  I think we were hoping that someone who had the adapters would rummage around the house to find a 6.3V wall wart to give it a try.

[adamct]

Out of curiosity (I'm really not inclined to spend any more time on this experiment, since I'm perfectly happy with my 12AU7s), how exactly would this work?

1. Would the adapter have to be exactly 6.3V, or would 6V suffice? When you first mentioned this, I looked around for 6.3V PSUs and didn't find any (I'm not saying there aren't any, just that my quick search didn't turn up any at the time, other than DIY options).

2. What modifications would be necessary? I assume I would have to remove or clip two of the pins from the bottom of the adapter (and maybe cover up the clipped pins to avoid any risk of electrical contact with the relevant holes in the Crack's 9-pin socket), and wrap the exposed leads from the PSU around two pins in the 6SN7 before inserting it into the adapter?

[Paul Birkeland]

1. Would the adapter have to be exactly 6.3V, or would 6V suffice?
2. What modifications would be necessary?

Look for wall warts that are 6-6.3V and rated for at least 300mA.  Something like this will work if you need to buy one.

To modify the Crack, snip the black/red pair of wires leaving pins 7/8 of the octal socket and heading to the 9 pin socket.  Snip them off at the octal socket.  Strip the wires back and solder them to the wall wart cord (cut the plug off, strip each wire back).  Heat shrink the joints.  It doesn't matter which wire is connected to the red, and which to the black when you're connecting the wall wart. 

There's a very, very slight possiblity of needing to add a ground reference to the 12AU7's heaters, but I wouldn't worry about it unless you get unusual amount of hum.

-PB

[adamct]

Ahhhh....OK, so the mod has to be made to the Crack itself. In that case, I'm definitely out. I'm happy with my Crack as-is, and with all of my mods, making any further changes would be a major undertaking.

[Grainger49]

Adam,

If you have a Wall Wart that is 6V@1A it will float high with a lower load.  These are not regulated power supplies.  But if you use 6V instead of 6.3V I think you are still within the range of what was specified.