[AMRadio] My Amplifer Quest took a strange turn today

Mon Apr 23 13:10:20 EDT 2007

My pair of 813's loaf along at 700 watts of carrier out,
unfortunately the antenna tuner does not.

I don't know what the pep would be, the power meter only goes up to
2000 watts and I have to guess by how hard it gets pinned.

That's plate modulated service, as an AM amplifier I would not
run it over 100 watts carrier. The 32V3 would put out the same
power so that's a silly idea.

For a reasonable boost, you need a LARGE amp with a LARGE power
supply, running at least a pair of 3-500z tubes, run off 220 volts,
then you can get 350 watts of carrier I think, which is the legal
limit if modulated correctly.

Brett
N2DTS

> -----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 11:04 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
> 
> 
>  
> 
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Bow
> Sent: Monday, April 23, 2007 2:39 AM
> To: 'Discussion of AM Radio in the Amateur Service'; Glowbugs
> Subject: RE: [AMRadio] My Amplifer Quest took a strange turn today
> 
>  Well, A bit of an update on my new toy..
> 
> I tested it today, after repairing some solder joints that 
> were not up to my
> specs and replacing some wire I didn't like that looks of.
> 
> The test was:
> Icom IC-718 --> MFJ-949E antenna tuner-->Amplifier-->Daiwa 3kw watt
> meter-->MFJ legal limit dummy load.
> 
> The IC-718 will do 100 Watts on CW/SSB/Rtty and 40 watts on AM
> 
> I used the frequency of 3870 kHz
> 
> I first used a RTTY signal 
> Input from Rig - Output from Amp - Grid Current (amps) - Plate Current
> (amps)
> 30 - 180 - .02 - .24
> 50 - 380 - .07 - .34
> 60 - 400 - 0.1 - .36
> 75 - 410 - 0.2 - 0.4
> 
> Next I tried an unmodulated AM carrier
> 
> 25 - 200 - .04 - .26
> 40 - 375 - 0.1 - .34
> 
> Final Check was on SSB, modulated to the peak ALC setting 
> with a 1 kHz tone.
> 30 - 110 - .02 - .16
> 40 - 200 - .02 - .18
> 50 - 210 - .02 - .22
> 60 - 300 - .04 - .22
> 70 - 375 - .04 - .24
> 80 - 400 - .06 - .26
> 
> I figured 80 watts was about as hard as I want to drive it.
> I don't have a High Voltage test lead here to actually check the plate
> voltage, but I am going to take this featherweight (NOT!!!) 
> into work with
> me and check it out there.
> 
> Here are some more photos, including the guts. I may just 
> rewire this thing
> for my own piece of mind.
> 
> http://riley-music.com/BowsStuff/AMP/14Guts.JPG
> 
> http://riley-music.com/BowsStuff/AMP/15TubeSockets.JPG
> 
> http://riley-music.com/BowsStuff/AMP/16Relay.JPG
> 
> http://riley-music.com/BowsStuff/AMP/17PWRSection.JPG
> 
> http://riley-music.com/BowsStuff/AMP/18MeterSwitch.JPG
> 
> http://riley-music.com/BowsStuff/AMP/19CapChoke.JPG
> 
> http://riley-music.com/BowsStuff/AMP/20FilTranny.JPG
> 
> http://riley-music.com/BowsStuff/AMP/21PWRTranny.JPG
> 
> http://riley-music.com/BowsStuff/AMP/22CoilSwch.JPG
> 
> I guess now I need to figure out how to do a few things.... 
> Get an opinion
> from someone who knows something about amplifiers and homebrewing....
> 1. Make it band switch able for 80/40/20/10
> 2. Figure out a tuned input for the above bands
> 3. figure out how to get it up to a 600 watt output level 
> (because everyone
> tells me the first 600 watts are the best for signal boost)
> 
> 
> Bow
> 
> W5EFR
> 
> 
> -- 
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> 11:56
>  
> 
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