HELP Vintage 12ax7's numbers what do they mean.

[James Rock]

I'm looking at 12ax7 's in particular RCA's. There are alot on ebay both NOS and used. WHat do the testing numbers mean I've seen two sets of numbers I'm confused.

The first sort say minimum is 32/32 and maximum is 64/64. Such as
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=370238432092&ssPageName=STRK:MEWAX:IT

The other numbers are 1200/1200 and other things in the thousands.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=380145150607&ssPageName=STRK:MEWAX:IT
And there are different ones still.
Like
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=250474979522&ssPageName=STRK:MEWAX:IT

I'm basically looking for some good RCA 12AX7's that I know will sound good but these testing results get me all confused. I understand 50's ones will be more expensive then 70's ones due to rarity etc not sure if there is much sound difference however.

 

[glassman]

Re: HELP Vintage 12ax7's numbers what do they mean.

First link: I have no idea what this scale represents

Second link: this appears to be the actual transconductance figure

Third link: this appears to be transconductance expressed as a percentage of the expected value

 

[James Rock]

Re: HELP Vintage 12ax7's numbers what do they mean.

Second link: this appears to be the actual transconductance figure

Third link: this appears to be transconductance expressed as a percentage of the expected value

So am I right in thinking the higher the percentage the better condition the tube?