Lin Robertson digital-conjurers at ROADRUNNER.COM
Thu Nov 27 03:33:09 EST 2008

At 08:07 AM 11/26/2008 -0500, you wrote:
>I agree that all tubes are not the same particularly when used in certain 
>critical applications as there are manufacturing variations from tube to 
>tube and from lot to lot.

This seems a good constant, but the real test is to repeat the 
experiment.  As I said, I tried the fix, and it worked like a charm.  The 
drift is gone.  (Thank God.) Now, I didn't have a large batch of 12AT7's to 
choose from...I just grabbed the only good Sylvania 12AT7 I had...and it 
worked.  Perhaps you'd like to drop a line to the author?    I think I have 
his email address, if interested.

It would be interesting to hear from others on this subject too; the 
scientific method is to repeat the experiment; well, it's been repeated 
once here, though not with a large sample batch.  Wonder if others have 
found this to be true in oscillator circuits?  Any RX-1 owners out there 
who have tried this fix?

In certain RF/IF/Osc circuits, this is probably useful info.  I think, at 
the very least,  in particularly touchy circuits, it can make a diff.

[On a side note, certain tube data seta, even in high-end tube tester docs, 
have had errors in them when it comes to grading the fitness of oscillator 
tubes in particular: I was interested to see several mid and late 30's 
6A7's and 6A8's flunk transconductance tests on a 539B that worked fine in 
the radios nonetheless.]

Roger on tube Mfg. being hard to pin down sometimes as to who actually made 
the tube. Annoying.

As for me, I've been in radio/telecom for only 40 years <grin>, worked for 
Teledyne-Ryan, Convair/GD, and finally was a prototype tech for the High 
Energy Physics Lab at UCSD.



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