[Boatanchors] 8122 Suitability/Selection (was: 6146 discussion on )

[Carl]

Every Burle and most any other 8122 Ive used in an NCL-2000 works without 
any modifications as it has a roughly -25 to -42V bias adjustment range. I 
have used a few Eimac 8122W's over the decades and had to modify the range 
adjust by using a different reference zener, these tubes were in the -44 
to -46V range. Modifying for individual bias pots allows using tubes that 
are not a true matched pair, about a 3-4V delta has no measurable effect on 
IMD. This is for 125ma idle current per tube in the SSB position.

The more positive the bias (towards the -25 side) the easier they are to 
drive so consider that if you have drive to burn and consider a higher 
number bias tube.

Since the NCL is swamped grid input there is no neutralization circuit.

Carl
KM1H


----- Original Message ----- 
From: "D C *Mac* Macdonald" <k2gkk at hotmail.com>
To: <james.liles at comcast.net>; <boatanchors at mailman.qth.net>
Sent: Wednesday, July 06, 2011 1:52 PM
Subject: [Boatanchors] 8122 Suitability/Selection (was: 6146 discussion on )


>
> Hi, Jim (and others).
>
> Might I ask how Burle 8122s can be correctly
> chosen for use in the National NCL-2000 amp?
>
> I have previously been advised that original
> NOS RCAs are no longer available at decent cost.
>
> * * * * * * * * * * *
> * 73 - Mac, K2GKK/5 *
> * (Since 30 Nov 53) *
> * Oklahoma City, OK *
> * USAF, Ret (61-81) *
> * * * * * * * * * * *
>
>
>
>
> From: james.liles at comcast.net
> To: boatanchors at mailman.qth.net
> Date: Wed, 6 Jul 2011 12:36:29 -0500
> Subject: [Boatanchors] 6146 vs 6146A vs 6146B or 6146W
>
>> SNIPPAGE <
>
> The reason that I followed with interest is the history of the 8122 seems 
> to
> draw a parallel. Some amplifiers will work with any 8122 and others will
> only work with about 3/4 of the production without modification, and 
> others
> cannot be made to operate properly with nearly 1 in 6 8122's. There is a
> broad range of bias and neutralization attributes involved. Burle is the
> only manufacturer that classified them with a four color code to enable
> intelligent choice.
>
> Kindest regards Jim K9AXN
> ______________________________________________________________
> Boatanchors mailing list
> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Boatanchors at mailman.qth.net
>
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1388 / Virus Database: 1516/3746 - Release Date: 07/05/11
>