A Virgin No More

[goozy]

Finished up my SEX tonight, all the resistances and voltages checked out fine, hook up CD player, phones in and cue up Dark Side of the Moon aaannndddd.......WOW,  verrry nice indeed!  All went well for a half hour or so then I thought I heard some rustling in the left channel, turn down the volume and its still there...damn. Shut everything down, pour another Guinness and let the tubes cool enough to swap sides. Start it all up again and sure enough after a half hour or so noise in the right channel!!
Looks like a got a bad tube, bummer.

Peter

[Paul Birkeland]

All 6DN7's are old, and many have been sitting around for a long time.  (Longer than I've been alive!)

There are several causes to the noise you're hearing:

1.  That 6DN7 needs 50-100 hours to cook in.  This sounds like a wishy-washy response to the issue, but we have literally received "defective" noisy tubes, run them in our own equipment for a week, then observed that the noise vanished. 

2.  That 6DN7 has oxidized pins.  Try cleaning them with a wire brush if they aren't shiny.

3.  There's a funky solder joint in the amp.  Since you swapped tubes, this seems unlikely. 

4.  You have sensitive headphones, and maybe ought to go to the 4 Ohm tap to lower the noise floor of the amp.

5.  The tube is actually noisy.

Seriously though, leave the amp on for the rest of the week, then see how things are this Saturday.

-PB

[mcandmar]

In my experience most 6DN7's start off noisy and need a good cook to settle down, some make a rustling sound, some hum loudly, but rarely are they quite out of the box. Its odd as i've never had the same issue with 6SN7's, 12AU7's etc.

[goozy]

Clean and cook sounds like a good plan. I'll hook some speakers up tomorrow and let my iPod run through for a week. I don't really like to out put into no load. I've split the difference and got the SEX wired up for 8ohms.

Peter

[Paul Birkeland]

In my experience most 6DN7's start off noisy and need a good cook to settle down, some make a rustling sound, some hum loudly, but rarely are they quite out of the box. Its odd as i've never had the same issue with 6SN7's, 12AU7's etc.

Yeah, I completely agree.  I think part of the reason is that most 6DN7's floating around out there are still true new old stock, while actual new old stock 12AU7's and 6SN7's are pretty uncommon, and the used tubes are already cooked in.

-PB

[Adrian]

DITTO on the "let them cook" comments.
I got frustrated with the S.E.X. 2.1 not being dead silent like the CRACK but took a deep breath and gathered my patience, eventually tried several 6DN7s and have now settled on the two that provide the least noise and best sound.
Patience...your reward is waiting.

[goozy]

A quick update. I let the tubes cook for 100 hrs. straight as suggested and that seems to have done the trick! After half hour of warm up there is just a very slight hum, no more rustle noise. Now I need to get rid of the ground loop with my computer.

Peter