[Amps] Drake L4B to 6 Meters Help

[Jim Thomson]

Date: Mon, 12 Dec 2016 13:05:34 -0500
From: "Michelle" <michelle_melt at windstream.net>
To: <amps at contesting.com>
Subject: [Amps] Drake L4B to 6 Meters Help

  Is it biased class "C" for CW usage on 6 meters?  If so it should do a
bit better that 65% efficiency.

   A pair of 3-500Z's can produce over a kilowatt if it has the plate
power that supports it.  (normally zero biased for linear operations
they should be biased at cutoff for class "C" operation.

   What condition are the 3-500Z's?

   If the Drake L4B is rated 1,000 Watts on CW I would not expect 1,000
Watts on 6 meters.

##  You cant run any high mu  GG triode in Class C on CW mode.  You will get 
key clicks badly.  Best you can do is lower the idle current  down to 5- 10-25 ma
for CW use. You will also have to increase the drive a bit to overcome the
increased, required bias voltage.   Then raise the idle current back up for SSB use. 

##  You could crank up the bias V to put it into class C....for FM use on 10M. 
Problem is, you cant tell the difference between class B and class C...both show zero idle current.
Keep increasing the  bias V...and idle current keeps going down down down, till it hits zero ma. 
Keep increasing bias V... and you are now into class C.   Increase it even more, and you are into deep class C.
Eff goes up a bit, but the harmonic suppression drops off.   Drive requirements skyrocket.   The input Z will change 
at that point, requiring re-tuning of the Pi tuned input. 

##  since u can only use class C  for 10M  FM use, I would not bother.  However, reducing idle current down to 10-40 ma
for CW use works great .   That works a lot better  and simpler  vs trying to cut off the idle current with various  bi and tri state electronic 
bias schemes.   The various bi and tri state EBS schemes work good on PTT  SSB, and thats about it.  They will cut off idle current between
words  on PTT.   They wont cut off between syllables.   If vox used, they are a wasted effort, and least effective.   Stop talking, and vox drops
off anyway. 

Jim   VE7RF