[R-390] Nuvistaplug? Other possible tubes.

[Mark Huss]

Besides, the receivers (HF and VHF) were terrable.  At least compared to 
the R-725's in the accompaning TRR-20.

Mark Huss wrote:

> I thought about 7963's as well, but for two factors.  First is that I 
> don't know of a good way of reducing the 150 volt B+ to under 100 
> volts.  The second is personal experence.  Two receivers, part of the 
> TRQ-23, that I worked on in the Army, used peanut tubes like the 
> 7963.  Every time I pulled them in for annual maintenance, I always 
> had to replace several of the peanut tubes for low gain.  It is like 
> they don't last as long when you run them for any length of time.  It 
> could have been the receivr circuits were designed too critical.  I 
> don't know.
>
> Kenneth G. Gordon wrote:
>
>> Mark Huss wrote:
>>
>>  
>>
>>> The installation 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.
>>>   
>>
>>
>> I am thinking that a better, much lower-noise, Nuvistaplug could be 
>> made using a single 7963 submini dual triode instead of the Nuvistors.
>>
>> The 7963 has far higher transconductance, 13000, than either of the 
>> two Nuvistors mentioned. However, its maximum rated plate voltage is 
>> only 100 VDC, so allowances would have to be made for that.
>>
>> Go here:
>>
>> http://pw2.netcom.com/~wa2ise/radios/penciltubes.html
>>
>> for details on submini tubes.
>>
>> And thanks for the plug to the Glowbugs web site. I administer that.
>>
>> Ken Gordon W7EKB
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>>  
>>
>
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