[AMRadio] My Amplifer Quest took a strange turn today


John E. Coleman (ARS WA5BXO) wa5bxo2006 at pctechref.com
Mon Apr 23 12:30:21 EDT 2007


Correction to: You have some parts there that could be very usefull and the
813s or capable of all you want and more, in class C service

Should read:

	You have some parts there that could be very useful and the 813s are
capable of all you want and more, in class C service.

When I'm in a hurry, "or" and "are" words are interchangeable.

Sorry, 
John, WA5BXO



-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of John E. Coleman (ARS
WA5BXO)
Sent: Monday, April 23, 2007 10:04 AM
To: 'Discussion of AM Radio in the Amateur Service'
Subject: RE: [AMRadio] My Amplifer Quest took a strange turn today

Bow:
	You need to start over if you want to get 600 watts carrier output.
A pair of 813s is just not capable of doing this in linear AM service.  150
to 200 watts is about it.  And you don't have enough power supply either for
large AM service.  Keep in mind that to get a carrier of 600 watts on AM you
must have an amplifier capable of over 2400 watts (4 X carrier).  Even so
there is another draw back in that when a linier amplifier is operated at
full drive and full output (lets say 2500 watts) its efficiency is 60-75
percent and with no input its efficiency is Zero percent.  With this in mind
you can figure that at 25% of the full drive power and output, that the
efficiency will be between 0 and 70 percent and in most cases it is around
25-30 percent.  This means that the amp can produce a lot more heat when
driven at 25% of full output than it does at full output. Hence the
probability of damage to light weight part is great.

There are some rules of thumb to be used for linear amplifiers in AM
service, and these rules are a lot different in requirements for big
equipment than the rules of thumb for SSB service.

This is the reason that many times it is better to use class C plate
modulated service instead.

You have some parts there that could be very usefull and the 813s or capable
of all you want and more, in class C service

I would be happy to help with some graphs and drawing to get you started if
you want to come by for so coffee.

The Computer Fixer
1622 Sawdust Rd. Ste A1
The Woodlands, TX 77380
281-367-6765

PS: bring Chocolate Chip cookies






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