No luck with tube rolling

[wolfhill138]

I built a crack with speedball a few months ago, and eventually did some upgrades - padded TKD pot, Audyn 100uf 400v caps, shielded input wires.  I love the way it sounds on my HD650s.  But I also tried some different tubes, and that hasn't been nearly as smooth sailing.

The amp is dead silent with the stock 1980s GE 6080, but when I switch to either of two different 1950s RCA 6AS7G tubes, I get this really annoying buzz that is clearly audible in quiet passages or between songs.  When the music is loud, the tubes sound incredible, but the buzz makes them unusable for quiet listening or certain tracks.  I've burned the tubes in about 60 hours at this point.  Tubes are from reputable suppliers - is this within the range of normal tube behavior or should I ask for a replacement?

With the input tube, I tried a 6SN7 adapter with a few different tubes, and get a ton of RF interference from other electronics in the room.  This audible interference changes with the volume.  Several 12AU7s, including the stock Sylvania, have all been dead silent at any volume position.

Any advice would be much appreciated!

[Paul Birkeland]

Not all the adapters are created equally. 
https://www.ebay.com/itm/255994277784?hash=item3b9a72af98:g:-PYAAOSwOyJX-neh
I think most people have good luck with that adapter.

You can try adding a 220 ohm 1/4W carbon film resistor between the wire going to pin 1 on the 6080 and pin 1 on the 6080, and the same on pin 4.  That may knock down what you're hearing, or it may not!

[wolfhill138]

Thanks Paul, I'll try that out!  It's the Garage1217 6SN7 adapter I'm using - it looks very well made.

[Toobuzz]

For what it’s worth, I have had the same experience with about 75% of the 6SN7s that I’ve tried in the C2A with the Garage 1217 adapter. I’ve concluded that it’s tube dependent. I have a 60’s Sylvania and a 50’s RCA 6SN7 that are silent, but most other 6SN7s (including new ones) seem to hum.

[2wo]

Keep in mind that any adapter,  no matter how well constructed can be a significant  compromise.

If you like 6sn7's, instal an Octal socket,  ain't that hard.

Then you can always get a 9 pin adepter 😏...John