[Heathkit] DX100 ANT

[Robert & Linda McGraw (K4TAX)]

One other factor relating to reduced tube life is power dissipation of Grid 
#2.  It is rated at 3 watts up to 60 MHz. and is reduced to 2 watts at the 
tubes upper operating frequency of 175 MHz.  With 250 volts applied that is 
a screen current of some 12 ma.  A class C amplifier incorrectly and lightly 
loaded may exhibit higher than normal screen currents.  Heath make no 
provision to monitor screen currents.

For a pair of tubes, 6146 or 6146A's, the recommended control grid current 
is 8 ma MAX or 4 ma per tube.  Experience has shown that drive levels, 
producing upwards of,  but not exceeding 4 ma per tube, lends to better 
modulation characterizes.  The safe and conservative range is in the area of 
3 to 3.75 ma per tube or 6 to 7.5 ma total.  It is important to know that 
the meter and associated meter shunt are such that accurate current values 
are indicated.  For AM operation, drive values of less than 3 ma per tube 
have been proven to cause modulation to suffer.  It is quite common, 
although Heath doesn't incorporate the concept, is to modulate the driver so 
as to attain higher drive levels on positive modulation peaks.  These short 
duration peak levels cause relative no increase in average driving power but 
do significantly increase the positive portion of the modulation envelope.

Your mileage may vary.

73
Bob, K4TAX





----- Original Message ----- 
From: "Glen Zook" <gzook at yahoo.com>
To: <mrapps at grandrapids-mn.com>; "Bob Young KB1OKL" 
<heathkit at mailman.qth.net>
Sent: Sunday, February 18, 2007 6:57 PM
Subject: Re: [Heathkit] DX100 ANT


> Another thing is not to run the grid drive over 5 mA
> and as little as 3.5 mA won't hurt anything.  Although
> RCA originally specified the 6146 grid drive as 4 mA
> per tube it was soon "discovered" that running them at
> much over 3 mA per tube greatly reduced the life span.
> The grid drive specification was then reduced to 3.5
> mA MAXIMUM per tube.
>
> The input (and output) power from a pair of 6146 tubes
> will not vary much, if any, from about 3.5 mA to over
> 8 mA but the life of the tube will be reduced by a
> substantial amount if you run anything over 6 mA and
> the life is increased quite a bit if you run between
> 3.5 mA and 5 mA.
>
> Glen, K9STH
>
>
> --- mrapps at grandrapids-mn.com wrote:
>
> Do not attempt to load the rig down for maximum output
> as would be done for running the finals as linears.
> You want rated plate current with rated grid drive and
> as much capacity remaining on loading caps as
> possible.
>
>
>
>
>
>
>
>
>
> Glen, K9STH
>
> Website:  http://k9sth.com
>
>
>
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