[time-nuts] Nuvistors and FETs...

[Don Latham]

You can also look up the gm of the nuvistors and get a reasonable match to a 
fet as well.
Don

----- Original Message ----- 
From: "J. Forster" <jfor at quik.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Sunday, May 02, 2010 9:23 PM
Subject: Re: [time-nuts] Nuvistors and FETs...


> Interesting idea. In fact, the later versions of the loop used FETs in
> place of Nuvistors. I've not compared the circuits.
>
> Because the thing is only 60 KHz, the change in grid/gate capacitance may
> not matter much. There may be some mounting and stability issues though
> because the plate caps were on the opposite side of a metal shield from
> the grids.
>
> -John
>
> ================
>
>> For what it may be worth, I've swapped Nuvistors out with FETS.  I
>> see from the schematic that the Nuvistors are running on 35
>> Volts.  It would be simple to drop the 35 Volts to 12 or 8 Volts with
>> a 3 terminal regulator in the receiver.  If desperation sets in, try
>> stuffing N-Channel FETs in place of the Nuvistors.  The gate is the
>> grid, the drain is the plate, and the source is the cathouse.  Since
>> the FETs are usually pretty low in capacitance you may need to shunt
>> the tuned circuit/s with a small piston type capacitor.  In one low
>> Voltage preamp circuit I used a National U-310.  In another one, a
>> Nems Clark receiver, I replaced the two RF front end ceramic triodes
>> stages that ran on 150 Volts with two U-310's and rewired the plate
>> supply to run off of the 12 Volts already in the receiver.  This made
>> for a low noise, very sensitive front end.  All I needed to do was
>> add a small quartz piston capacitor to bring the tracking in at the
>> high end and the bottom end fell right end.  If you can make that
>> work, you'll never have to replace those pesky wittle Nuvistors again.
>>
>> Burt, K6OQK
>>
>>
>>>From: paul swed <paulswedb at gmail.com>
>>>Subject: Re: [time-nuts] 6CW4 Nuvistors on eBay...
>>>
>>>
>>>Indeed there are.
>>>And even 7587s thats the TRF frontend. In one of the units V3 appears bad
>>>all Rs are good voltage high on plate, 0 cathode current. But oddly when
>>> I
>>>swap v1 into position same effect so somethings odd. Or my methods not
>>>correct.
>>>The other units working. Had to replace a shorted 6.2 V zener.
>>>The 100 kc vco /lock osc is awful touchy.
>>>Pretty amazing the units pretty hot sensitivity wise -80 dbm.
>>>Interesting afternoon. Way in the deep corner of the basement I think I
>>> may
>>>have a nuvistor or two. Time to see what they are.
>>>
>>>On Sun, May 2, 2010 at 4:14 PM, Burt I. Weiner <biwa at att.net> wrote:
>>>
>>> >
>>> > For what it's worth, I just took a look and found a bunch of 6CW4's on
>>> > eBay.  See:
>>
>> Burt I. Weiner Associates
>> Broadcast Technical Services
>> Glendale, California  U.S.A.
>> biwa at att.net
>> K6OQK
>>
>>
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>
>
>
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