[Boatanchors] Tube tester results question

[bonddaleena at aol.com]

Hi to all. I have what is probably;
"Ron's dumb question of the week", but I gotta ask anyway....

A lot of my boatanchors use a 6BA6 or even a 'hotter' tube like the 
6BZ6. There's two 6BZ6s in my R-1051B. I know enough to realize that 
swapping tubes calls for circuit changes, etc. However, it's fun to 
replace a 6BA6 in an old radio with a 6BZ6 and enjoy the additional 
gain.
Last week, in my 'notes' I found a note that said that a 6JH6 was even 
better than the 6BZ6.
So I looked on ePay, er, eBay and a chap was selling 5 NOS / NIB 
Sylvania tubes for $9.99.
I have 2 testers, one is just a simple Sencore 'Emission / Leakage / 
Short tester'. The other one is a nice older Weston Transconductance 
tester. I use the Sencore 90% of the time, just because it a quick 'go 
/ no go' test. I tested the tubes in the Sencore today and they all 
tested exactly the same, good.

Here's my question:

However, I noticed a curious thing, when switching the tester from 
'emission' to 'leakage'. I usually flip the switch as soon as the 
emission reading goes upscale and stops.
With these 6JH6s, the 'leakage' was very high initially, but came down 
to zero after a short period. I have noticed other (different numbered 
tubes) do the same but not nearly as slowly as the 6JH6s.... Why is 
that?
For example, I can but a good 6BA6 in the tester and as soon as the 
emission needle stops, I can switch to leakage and the needle will be 
at zero, no dropping seen.
By the way, all 3 of the tubes mentioned above use the same set-up 
readings.

I know this is a dumb question, but I just wanted to understand this 
phenomenon. I wonder if it has to do with construction, 
transconductance, ??????

thank you!!!

ron
N4UE