[Boatanchors] AM linear question

[Gary Schafer]

I wouldn't talk too long with 150 watts output on AM with a 30L1. you will
be exceeding the plate dissipation of the tubes.

If the amp is tuned up for 600 watts output as you normally would, you then
reduce the drive to produce a carrier of 150 watts (25% of output)for AM. 

At 600 watts output the efficiency of the amp will be around 60%. At 150
watts carrier output the efficiency will be around 30%. This is normal
operation for a linear amp on AM. 

At 30% efficiency and 150 watts output the input power will be around 500
watts. 500 watts - 150 watts leave 350 watts of plate dissipation!
811A's as I remember have a plate dissipation of only 65 watts each. For
four of them that is 260 watts so you are exceeding the plate dissipation of
the tubes by 90 watts in this mode of operation.

On SSB the average power of the amp is much lower that it is on AM so the
tubes are not stressed so much unless you hold the carrier on at tune up or
run very heavy processing.

By the way if everything is set up properly the plate current shouldn't
increase with modulation. It should just wiggle around a little.

73
Gary  K4FMX

> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf
> Of D C _Mac_ Macdonald
> Sent: Monday, December 07, 2015 9:35 PM
> To: RAY FRIESS
> Cc: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] AM linear question
> 
> If you set the exciter rig's output to hold the AM carrier output of the
> 30L-1 to 30% of the "normal" CW output, you should be safe.  Keep the
> exciter's modulation down to the point where the 30L-1 current
> "flickers" upward about 30% more than its idle current with RF drive but
> NO modulation and I think that you should be safe.
> 
> * * * * * * * * * * *
> * 73 - Mac, K2GKK/5 *
> * (Since 30 Nov 53) *
> * k2gkk hotmail com *
> * Oklahoma City, OK *
> * USAF & FAA (Ret.) *
> * * * * * * * * * * *
> 
> 
> > From: rayfrijr at msn.com
> > To: boatanchors at mailman.qth.net
> > Date: Mon, 7 Dec 2015 19:33:12 -0700
> > Subject: [Boatanchors] AM linear question
> >
> > Having been a ham for nearly 50 years now, I should know this, but I
> wanted to get input from
> > some of the other old timers ... perhaps from Glenn.
> >
> > I have two 30L-1 linears and I'm curious as to whether or not I
> could/should use them on AM, and if
> > so, should they be run at reduced power or with other restrictions.
> >
> > Thanks guys...
> 
> 
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