[Heathkit] DX-40 Questions

[Carl]

A problem with low grid drive in a plate modulated Class C final is 
distorted modulation. The tubes be they a 6146 or a 4-1000A really need to 
be biased and driven into hard Class C and only a modulation monitor will 
tell you when its tuned correctly.

While not applicable (I dont believe but not sure about CC modulation) to 
the DX40/60 it covers a lot of other rigs. My Viking II (6146's originally 
and now 6146B's) is an example of needing a scope on the output with either 
version.

Carl
KM1H


----- Original Message ----- 
From: "Glen Zook" <gzook at yahoo.com>
To: <heathkit at mailman.qth.net>; "rbethman" <rbethman at comcast.net>
Sent: Wednesday, November 03, 2010 1:38 PM
Subject: Re: [Heathkit] DX-40 Questions


> RCA started out with 3.75 mA for the maximum grid current of the 6146. 
> Then they dropped it to 3.5 mA and finally to 3.0 mA.  I have found that 
> the 6146 series is very happy with less grid drive.  In fact, all the way 
> down to about 1.75 mA works fine with no drop in output.
>
> Over driving the 6146 series is the most common cause of failure.
>
> Glen, K9STH
>
> Website:  http://k9sth.com
>
>
> --- On Wed, 11/3/10, rbethman <rbethman at comcast.net> wrote:
>
> The DX-60 manual specifically states to tune the grid to NO MORE THAN 
> 2.5mA or damage to the final will result.
>
> It would appear that "they learned from the past".
>
> I know in tuning according to this, I have NEVER taken out the single 
> 6146!
>
>
>
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