[R-390] Nuvistaplug?

[Mark Huss]

The instalation manual and schematic is here: 
http://www.mines.uidaho.edu/~glowbugs/receivers.htm see item number 7.
I figure you can either use it unmodified (will have to substitute 
6CW4's for the 6DS4's, because the 6DS4's won't handle the higher B+ 
voltage) and sacrifice AGC control of the first RF Amp, or you can 
rewire pin 8 of the first 6DS4/6CW4 to connect to the unused pin 2 of 
the seven-pin plug to restore some AGC operation.
 In 2004, W3CRR was going to build one, and wondered if there was any 
interest in copies.
Now, the 6CW4 has a higher noise than the 6DS4, but the 6DS4 is rated 
for only 135VDC plate voltage.  Can any tube gurus out there tell us if 
using a 6DS4 as the first tube and a 6CW4 as the second would be safe?  
This might give a better noise figure than two 6CW4's.
Further thought tells me that most receiver locations would have an 
ambient noise at their location to make this no real improvement except 
above 20 MHz.

pete wokoun, sr. wrote:

> Never heard of this one.  Any chance you could scan the circuit and 
> make it available?
>
> pete
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>> From: Mark Huss <mhuss1 at bellatlantic.net>
>> To: R-390 at mailman.qth.net
>> Subject: [R-390] Nuvistaplug?
>> Date: Thu, 22 Dec 2005 21:21:08 -0500
>>
>> Here is one for all the experts.  A plug-in modification for SP-600's 
>> was the Nuvistaplug.  This was a replacement for the first RF 
>> amplifier in SP-600 that substituted a pair of 6DS4's in a cascode 
>> circuit.  The resulting 6 to 9 dB increase in Signal to Noise level 
>> made the SP-600 sound like a new receiver.  My brother recalls that 
>> there was a similar modification using a 6CW4 for the R-390A, popular 
>> with MARS operators.  I happened across the schematic today, and it 
>> looks like with changing one pin in the Nuvistaplug, you could drop 
>> in the replacement for the 6DC6.  This should increase the signal to 
>> noise level of the first RF Amp.  So has anybody even heard of this 
>> being attempted?
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