[Boatanchors] tube question

[Carl]

The 12B4's are notorious for developing leakage in that boatanchor, the 
others just seem to loose steam.

My first experience with the 606A was at National in the 60's and Ive had my 
own about 7 years now which replaced a URM-25D and is now paired with a 
8640B.

There is a small electrolytic that causes modulation problems, upper right 
side if I remember, I dont have the manual handy.

Carl
KM1H



----- Original Message ----- 
From: <bonddaleena at aol.com>
To: <test-equipment at mailman.qth.net>; <boatanchors at mailman.qth.net>
Sent: Sunday, April 18, 2010 5:22 PM
Subject: [Boatanchors] tube question


>
> Hi. I have what may be a 'dumb question', but I'd like to be able to learn 
> more about vacuum tubes.
>
> I have several pieces of HP test equipment, but the one that sees the most 
> use, is my HP 606A. Lately, the Modulation and RF output pots have become 
> flaky. I have had this jewel a LONG time, and it has been moved a LOT. I 
> was tired of looking at it's ugly cover, so this week I pulled it apart 
> and did a restoration. While it was apart, I tested all the tubes. Man, 
> there's a bunch in there!
> Anyway, I found one tube with a 'short', but what I am asking concerns the 
> result of  'Leakage' testing.
>
> I have several tube testers including a nice Weston Transconductance 
> tester. However, my Sencore TC-142 gets the most work. I realize this is 
> pretty much a 'go - no go' tester, but here's my question:
>
> Testing several of the tubes, the 'emissions' test was fine, but when 
> switching to 'leakage', some of the tubes showed very high leakage, 
> initially. However, the longer I left the tube in the tester, the leakage 
> came down to an acceptable level.
> When testing a NOS spare of the same #, switching from 'emission' to 
> 'leakage', immediately, shows ZERO leakage.
>
> Is this a situation where the grid is contaminated?
>
> The generator is a remarkable piece of Engineering. I could NOT imagine 
> what it would cost in today's $ to build a tool like this, castings and 
> all!
>
> As with all my tube equipment, I installed two, small muffin fans to move 
> the air around......
>
>
> thank you in advance!
>
> ron
> N4UE
>
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