[Hammarlund] NuvistaPlug & more

[rrkrr at comcast.net]

The stock 1st RF amplifier tube in the SP-600 was a 6BA6 - a remote cutoff pentode.  The 6BA6 has a relatively high noise figure which becomes a very significant limitation to receiver MDS above 20 MHz or so.  The "Nuvistaplug" used two 6DS4 remote cutoff Nuvistor triodes connected in cascode, which gave good gain, much improved noise figure, and high reverse isolation for the 1st RF amplifier.  The Nuvistaplug was sold as a tube socket plug-in replacement for a number of 7 pin tubes.  The tube socket connections of the Nuvistaplug must have been adaptable to the particular device to be replaced.

The British companies Racal and Eddystone liked to use cascoded triodes for 1st RF stages in their receivers.  They used the ECC189 (American type 6ES8) which is a single 9-pin miniature tube containing two triodes that are designed to be connected in cascode.  In order to use this tube in an SP-600, the 7-pin 1st RF amp tube socket would have to be replaced with a 9-pin, and the resulting noise figure would probably not be as good as that for the Nuvistor.

The 2nd RF amp in the SP-600 is also a 6BA6, but with the gain of the 1st RF amp in front of it, the noise of the 1st RF amp dominates, so it's not worth replacing the 2nd RF amp with a lower noise device.

Bob K4ERR


 -------------- Original message ----------------------
From: "ChasW3KC" <w3kc at verizon.net>
> For the SP-600, what tube type did the NuvistaPlug replace?
> Was it ever used in radios other than the SP-600?
> As I recall,  Ameco used to make a preamp that used 
> nuvistors
> (the Ameco preamp I have is solid state and I think it came 
> out later).
> TNX/73 de Chas W3KC 
> 
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