[Boatanchors] VT-269

[Rich Post]

Yes, agree that the 717A would be more useful as a high freq RF amp.  The 
only advantage for IF would be the higher transconductance and there are 
and were better options.  Even the SX-28 grew from all 6SK7 to using a 6AB7 
here and there.   But the hams of yester-year shouldn't be quickly 
discounted as foolish.  For many of their uses, AVC  was not important and 
the RF amp stage was often maxed.  Getting the last bit of gain and 
signal-to-noise on weak signals was of utmost importance.

However, the WE-717A may be better suited as spares to folks who buy an 
audio amp that uses them, like a Yamamoto A-08.  But if you are well-heeled 
and foolish enough to buy one of those, then you can afford 
new-old-stock  ;-)

Rich KB8TAD

At 08:13 PM 2/4/2010, Al Klase wrote:
>Well, the word "boondoggle" comes to mind.  Yes, you might be able to
>eek out a little noise figure improvement on 10 meters by installing a
>sharp-cutoff pentode in the first RF amp, but you're screwing up the
>gain structure and AVC action of the receiver, resulting in distortion
>on strong signals.
>
>Putting sharp-cutoff tubes in the IF is an even worse idea.
>
>A properly restored SX-28 qualifies is a high-performance receiver in
>stock trim.  If I were looking for a plug-in tweak to the front end I'd
>try 6SG7's.  These were the next generation RF (remote-cutoff) pentodes,
>and were used in the AR-88.  Their performance is equivalent to the
>post-war 6BA6's.  Higher transcondance means not just more gain, but
>better noise figure. However. the importance of being able to control
>all the available gain cannot be overemphasized.
>
>There are parallels between the development of vacuum tubes in the
>1930's and '40's and today's progress in CPU's and memory chips.
>Significant improvements were made every 12-18 months.
>
>Al
>
>On 2/4/2010 5:19 PM, Mr. and Mrs. Magoo wrote:
> > An SX-25 came to me with a VT-269 plugged into a socket where a 6SK7 should
> > be.  I can find references to the VT-269 and a cross to a WE-717A, but I
> > have no data for testing nor do I have a base diagram.  Does anyone know if
> > it is, in fact, compatible with a 6SK7?  One source suggested a 6SJ7 "with
> > wiring changes"!
> >
> > Bill VE3NH