[Hammarlund] Nuvistor Front End of Sp-600

[rrkrr]

The issue with the 6BA6 as the 1st RF amplifier in the SP-600 is that 
its high noise figure becomes important at the high frequency (above 30 
MHz) end of the range.  It really is horrible.  It's bad enough on 10 
meters.  The circuit that used two nuvistor triodes in cascode 
("Nuvistaplug" - Google that and you'll find the circuit) really made a 
difference when trying to use the SP-600 on 6 meters. 

There is also a dual triode in a standard 9-pin miniature tube base that 
was designed for connection in cascode circuits and has low noise figure 
- the 6ES8/ECC189.  These were used in the front end of Racal 17L 
receivers, which were designed a few years later than the first 
SP-600s.  The 6ES8 American version was used in TV tuners.  These 
require a larger socket at the first RF stage than the 6BA6 and are not 
quite as low noise as the nuvistors, however.  If you want a low noise, 
remote cutoff nuvistor triode for the input stage of the cascode, use 
the 6DS4.  See:  <http://en.wikipedia.org/wiki/Nuvistor>

Bob K4ERR


stanleybadams wrote:
> I think you might want to think what you are going to use the radio for.
> Casual listening to AM radio?  SSB or AM amateur (for SSB you need the
> product detector which is a far better mod in my opinion).  Do you want to
> hear TV stations on the upper bands as they go away after 2009, unless they
> repeal the date?  I do not think that there really is any bang for the buck,
> now if you were on Guam copying teletype from the states or ships at sea,
> that might be a diff thing.   I would suggest the 6BZ6...A very good
> remote-cutoff tube as a direct replacement for the 6BA6. No other tube seems
> to work as wellwithout changing a few other parts around. Or the 6SS
> whatever the last part is 6SS6 or 5?  That was a lower noise tube for TV
> tuners.  AM band has gotten noiser with the addition of IBOC and their extra
> carriers in the day time anyway.
>
> Best to you
>
> Stan Adams
> Memphis
>
>
>
>
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