First Build: Bad Tube

[gabriel]

I just completed construction of the Eros 2 and am wondering whether I have a bad tube and/or broke it.

Just after completing I listened to some music and it sounded wonderful at reasonable volumes.  However at semi-loud volume with nothing playing there was a fluttering in the left channel (helicopter sound), and a pretty reasonable buzz in the other channel.

Today I went through the wiring again and discovered some untrimmed wires touching the metal chassis.  I trimmed those, and there's much less noise and buzzing only at even higher volumes.  However one channel is now VERY quiet.  When I swap the EF86 tubes, the quiet channel swaps.  The tube which was generating the helicopter sound is now the very quiet tube.

Did I kill the tube?  Is the tube dead / the problem do you think?  Thanks for any help.

edit:

I just redid my resistance and voltage checks.  They were perfect immediately after completing the build.  Now the voltage checks are not.

IA,  IB 210-230V --> 215.2, 214.5
OA,  OB 155-185V --> 168.5, 145.0
OC,  OD  95-100V -->  95.3, 114.0
OkA, OkB  95-105V -->  96.7, 113.8
OkC, OkD  0.7-2V -->  1.28, 0.007

Do you think these measurements indicate a failed tube?

 

[Paul Birkeland]

The OKC/OKD voltage follows an EF86?

If so then yes, it's possible that one of those leads touching the chassis exhausted the EF86.  I just wrapped up an Eros 1 repair last week that had a similar issue that destroyed a brand new EF86 in the process. 

 

[gabriel]

Thanks Paul.  Those voltages do in fact follow the "bad" EF86.  Looks like I killed a tube.

 

[Paul Birkeland]

Oh yeah, that tube is just totally refusing to conduct!