Here's the summary of the tests George (aka Tubulab) did on SE 6av5. It's what got me interested in the tube and I'm glad I got the chance to try them in push pull at least.

http://tubelab.com/articles/tube-tes...v5-sweep-tube/

sudden hum from LP-2030
 

Hi all,
A few days ago, I started hearing a hum from my speakers when no music was playing.
I detached everything except my KT88 Firebootle and powered it up - silence through my speakers, even with my ear pressed to the drivers.
I then connected the LP-2030 to the Firebottle via my normal interconnects, with nothing attached to the LP-2030, and powered the two up - the hum returned.
The hum increases as I raise the volume knob, and more strange, is present even when the selector switch is on "mute".
I tried swapping all of the tubes, but the hum persists.
I tried using a "cheater plug" on the LP-2030 to see if it is a ground loop hum, but that made no difference either. Does anyone have any suggestions?
Thanks so much,
Chris

Have you ever turned on the amplifier without tubes? Tighten the knob from the fuse holder, I had this problem with the phono station, must have come loose when I put it on the shelf

Hi cgn-dt-n,
I did try removing the fuse, polishing the ends, treating with contact enhancer, and re-installing. This did not resolve the hum.
I did not think you could turn on a tube amp with no tubes installed - doesn't this cause damage? Sorry if this is a dumb question, but I am not very tube savvy.
What would this reveal if I were to try this?
Thanks again,
Chris

I'm not a technician myself, but I switched on all of Dennis' amplifiers without tubes when they were first put into operation to determine the polarity of the power plug. It didn't cause any damage. Some of the 01A I used were very microphone sensitive and some caused a hum. This way, you can rule out at least one fault with the pre amp

Thanks! I'll give this a try. Did you have reason to suspect that the polarity of the power plug was reversed on your gear? Was it? How did you check this?
Thanks again,
Chris

In Germany, the plug fits into the socket in both directions. I use the phase detector from MFE or Oelbach to check the polarity

Ah; sorry; I ethnocentrically assumed you were in North America - my apologies.
That makes much more sense now. Since our plugs have 3 prongs, I was unclear why you thought to check the polarity unless you suspected the gear had been wired wrong.
Thank you, and again, my apologies,
Chris

Why apologize, everything is ok. Yes, Dennis is also known on the other side of the Atlantic with the companies Carey and Inspire. I like the way he tunes his amps. Fits perfectly with my hearing habits and speakers. That's right, the idea came from polarity, not every manufacturer adheres to the norm. I didn't consider the 3-pin plug. Bad experiences, on the other hand, with some 01A. Greetings from the holiday on the Mediterranean sea.
PS Cgn- dt-n Cologne Downtown north

Thanks! Did you happen to find any suppliers of consistently low-noise/microphonic 01A tubes? Enjoy your Mediterranean holiday!
Best,
Chris