[R-390] Nuvistaplug?

Sat Dec 24 20:40:35 EST 2005

Group,

Well whatever the SP-600 may lack in performance against the R-390A (the 
boys radio I'm told) it makes up for in it's tuning system, audio and 
classic looks......we don't call any of them "Depot Dawgs" either do we Mr. 
Moorer. (does have a pedigree though!)

It's molded paper caps fail just as often as the ones in the R-390A and the 
government never set a mountain of them out in the weather for an extended 
period (that I've heard about anyway)....which has been blamed for the 
failures of those in the R-390A.  Much scientific testing, such as boiling 
(or was it baking) and freezing of them many times over to simulate the SJC 
conditions has been conducted, as I understand it, to substantiate that 
conclusion.  (results published elsewhere)

HA!....just a little Christmas Eve fun folks...they are both great radio's 
and I am proud to own several of each!

Merry Christmas to all....

Cecil Acuff
WB5VCE
Gulfport MS (Katrina Central)

----- Original Message ----- 
From: "Mark Huss" <mhuss1 at bellatlantic.net>
To: "Michael Murphy" <mjmurphy45 at comcast.net>
Cc: "r390 net" <r-390 at mailman.qth.net>
Sent: Saturday, December 24, 2005 6:16 PM
Subject: Re: [R-390] Nuvistaplug?

> In that case, the 6DS4 or 7963 may well work.  Now, if Anybody runs across 
> a Nuvista-Plug, Stock number 5960-H00-9058, grab it so we can drop it into 
> an R-390A and see how much improvement we get.  I'm betting there will not 
> be that much, but would be interested to find out.  And if not, then one 
> can always sell it to a poor SP-600 owner so that he can get reasonable 
> performance out of his receiver;)
>
> Michael Murphy wrote:
>
>>Mark,
>>
>>I don't know if anyone talked about the voltage situation.
>>As far as voltage goes, the cascode circuit can be done in a parallel or
>>series bias configuration with good results. In the parallel, the stages 
>>are
>>usually cap coupled and each tube is given the full B+ voltage through a
>>choke or tuned circuit. In the somewhat simpler series cascode
>>configuration, sometimes preferred in VHF and UHF circuits, each stage 
>>gets
>>around half of the B+. The series circuit is commonly used with bipolar 
>>and
>>J-FET circuits as well.
>>
>>Mike WU2D
>>
>>
>>----- Original Message ----- 
>>From: "Mark Huss" <mhuss1 at bellatlantic.net>
>>To: "pete wokoun, sr." <pwokoun at hotmail.com>; "r390 net"
>><r-390 at mailman.qth.net>
>>Sent: Friday, December 23, 2005 8:22 AM
>>Subject: Re: [R-390] Nuvistaplug?
>>
>>
>>
>>>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
>>>>
>>>>
>>>>
>>>>
>>>>>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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>>>>
>>>>
>>>>
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>>
>>
>>
>>
>
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