[HBR] Re: GB> 1929-Style "QST SUPER 12" Receiver: UPDATE

[Kim Herron]

Hi Gang,

      SNIP
>Well, to anyone complating the construction of a receiver like this
>utilizing ancient tubes---or ANY tubes, probably, for that matter---do not
>always suspect the worst when trouble-shooting...!
>
>The moral of the story is simply this: even if your tubes pass muster on a
>dynamic tube tester, it is NOT an accurate indication of how they'll
>perform "...in the field". Both of these old 224A's were NOISEY in their
>specific applications, for whatever reason(s)---and yet both had
>transconductance levels just in excess of 800 umhos.

      This is why the radio manufacturers always suggested substituting a 
known good tube,
or trying the tube in another radio that works.  Tubes testers are just 
that.  It's very difficult to
tell how the thing will work until it's in a circuit.  Testers give a good 
indication of tube condition
but can't be relied on for the final answer.  I keep a stock of about 500 
tubes that I KNOW work
because I've tried them in the various radios that I work on.  When 
possible, I test tubes that I've sold
the same way.  Even NEW tubes can be toast.


Thanks!!

Kim Herron
1-616-677-3706