[adhoc]

Hello all,

I'm in the market for WE 421A tubes right now, however, I'm having a bit of a problem - all the ones I'm coming across appear to test unacceptably!

So far, on a TV-7/DU tester, the majority of the 421As that i'm coming across test 60/60 with 40 as the minimum. Is this normal?

taking into account that a 6SN7 should test 100-120 on a TV-7 to qualify as 'tested as new', and assuming that both tubes use the same 'scale' when tested on the TV-7, doesnt that mean that the tubes i've come across so far are all middle-aged? it doesnt help that i know of at least one TS 5998 that tests 60/60 NOS NIB too.

help!

 

[jamato8]

The 5998 and 421A should test about the same so if you have a nos testing at 60 I would use that as a guide.

John

 

[Hirsch]

Tube testers are notorious for sometimes misrepresenting tubes. This could be due to errors in the tube data chart, or simply the way that the tester measures. Even with a calibrated tester, some tubes just appear to measure low (or sometimes high). Best bet is to learn how your tester measures a tube by measuring tubes that are known (if NOS, or if your seller has provided test measurements). Eventually, you'll get a feel for how your tester measures a particular tube which will give you better insight into the tube than the scale reading. Use the life test on the tester. It should produce a 10% voltage drop (I don't know that particular tester, but that's how it worked on the ones I've had). If the tube at lower filament voltage is able to maintain Gm 10% or closer to the Gm produced with full voltage, then the tube is likely near NOS regardless of the tester reading.

 

[Bobziolk]

The gain doesn't tell the full story. When processing the activation of the cathode the filaments are over heated to get the cathode to give off electrons. It is actually dead until that is done. You get a bell curve of activity that should be on the low side of the curve. During operation you go up the curve with life. So you don't know what side of the curve you are onby reading gain.  Over processing would put you on the other side of the curve and further life would degrade the tube. So a low gain reading  is good for long life as you go up the curve and get better gain till you are on the other side and it starts it degrade.From my old days at TS Bloomfield, NJ.in Advanced. Development Dept.
I

 

[eserafinojr]

Your insight was interesting but you do realize this thread is 11 years old right? 

 
The OP's question seems like it was answered to me!

 

[jamato8]

  Your insight was interesting but you do realize this thread is 11 years old right? 

 
The OP's question seems like it was answered to me!

Within the realm of time, 11 years is a blink of the eye or less, though many tubes may have come and gone. Life is relative or non relative, depending up the perspective. :^) 

 

[theredmantra]

Your insight was interesting but you do realize this thread is 11 years old right?

The OP's question seems like it was answered to me!

And 7 years after that I found this post and appreciate all the information.