[AMRadio] Any amplifier suggestions?


John Coleman jc at pctechref.com
Mon Oct 5 11:26:40 EDT 2009


Todd, 
Typically the linear amp will be the fewer parts and expense but with less
output than a full plate modulated class C rig per a given tube.  One of the
simplest tetrode linear systems is to put a 50 ohm load resistor right on
the grid of a big jug like a 4-1000 or a pair of 4-400s and use a zener to
bias the cathode circuit or fil return. It will also require a screen
supply.  The idea in all of this is that if the grid is loaded with a 50 ohm
dummy load, then it will not require tuning.  The small amount of input
capacitance will be negligible on the lower freq bands.  And it should not
require neutralization.  

OTH, If you are going linear with a triode or triode connected tetrodes then
you will want to go to a grounded grid linear.  No screen supply, no
neutralization, but does require more drive and/or may require drive tuning.

You may expect very poor plate efficiency in any linier amp that is tuned
properly to work with an AM input.  

If you're looking for old style circuits that are proven to have the most
output with the least plate dissipation (smallest tubes) then plate
modulated full class C finals with push pull class B modulators is best.
More work more parts, but well worth the time and effort in the long run.

My favorite in small legal limit stuff would be a pair of 812s push pull
class C, modulated by a pair of 811a is class B. 

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Todd Carpenter
Sent: Monday, October 05, 2009 9:30 AM
To: AMRadio at mailman.qth.net
Subject: [AMRadio] Any amplifier suggestions?

I am interested is a simple design hf amplifier for am cw on 160-80/75-40.
These are the bands i operate on where the extra power would help. Fewer
parts count the better. Ultimately lower cost the better. I have power
supply parts and believe that i can generate around 2000 volts. I am slowly
researching tubes and am leaning toward 2 or 4 tubes that can basically
generate lots of watts at half to two thirds their ratings to prolong their
life span. Perhaps tubes such as 811's, 810's, 833's, 4-400's. I am open to
suggestions. I will need to build or acquire a heavy duty matching system as
part of the amp. My goal is at least 300 Watts AM. I do not want to mess
with systems that require cooling other than fans. I am not interested in
modes for this amp other than am and cw. It will almost exclusively be used
for am as i rarely use more than 5 watts on cw any way. Simpler cheaper is
better for me. I appreciate your suggestions. Todd  
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