[Boatanchors] AR-88LF HB Pre-selector: UPDATE

[Al Klase]

I'm with Carl.

Gain is nice, BUT you need to be able control it especially in a 
communications receiver.  This is the reason for remote- and 
semi-remote-cutoff pentodes.  Unless you're running that tube wide open 
all the time, you'll be much better off with the semi-remote-cutoff 
6GM6.  It's transconductance is 13,000 umohs versus 18,000 for the 6JK6, 
so it's no slouch in the noise/gain department.  When you try to reduce 
the gain of a sharp-cutoff tube you get inter-modulation distortion.

My two cents,
Al

Carl wrote:
> Some of the audiophools pay big Pesos for that tube as its used in a few 
> high end FM tuners.
>
> I prefer the 6GM6
>
> Carl
> KM1H
>
>
> ----- Original Message ----- 
> From: "Edward Swynar" <gswynar at durham.net>
> To: <rca at mailman.qth.net>; <antiquewirelessassociation at egroups.com>; 
> <boatanchors at mailman.qth.net>; "Welcome to the Novice Rigs List!" 
> <novice-rigs at mailman.qth.net>; <AmRadGear at yahoogroups.com>; 
> "homebuilttuberadios" <homebuilttuberadios at yahoogroups.com>; 
> <hbr at mailman.qth.net>
> Sent: Tuesday, April 14, 2009 3:16 PM
> Subject: [Boatanchors] AR-88LF HB Pre-selector: UPDATE
>
>
>   
>> Good Day,
>>
>> Wow, and DOUBLE wow...!
>>
>> I did some research through my 1971 edition of the "Sylvania Receiving 
>> Tube Manual", in a quest for possible "hotter" tube substitutes for 
>> the 6DK6 that I placed inside my recently homebrewed AR-88LF 
>> pre-selector:
>>
>> http://www.flickr.com/photos/15888272@N05/?saved=1
>>
>> I found several with the same pin-outs as the 6DK6, but by far, *THE* 
>> hottest candidate appeared to be the 6JK6 (almost TWICE the 
>> transconductance / mu of the former)...and, as GOOD luck would have 
>> it, ye olde junque box yielded a "primo", NIB Sylvania-brand 6JK6.
>>
>> I''ve just finished installing it inside the pre-selector, and as I 
>> said earlier, wow and DOUBLE wow...! This thing is REALLY smokin' 
>> now --- indeed, on the lower frequencies, I have to retard the 
>> pre-selector's RF gain somewhat to keep it from "taking off".
>>
>> But what a minor inconvenience, when compared to the tremendous and 
>> VERY worthwhile improvement this small tube has afforded the rig's 
>> overall sensitivity...
>>
>> If you're at all contemplating the construction of a pre-selector for 
>> YOUR BA receiver, do consider acquiring a supply of the 6JK6 tube ---  
>> I don't think you'll regret your decision!
>>
>> ~73~ Eddy VE3CUI - VE3XZ
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>
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/