[AMRadio] Amplifier to use with my DX-60


kenw2dtc kenw2dtc at comcast.net
Thu Mar 16 20:24:57 EST 2006


Jim,

I guess my question is really:  Can anyone actually demonstrate a real AM 
linear that can output 500 watts carrier and show 2000 watts PEP into a 
dummy load with a nice looking audio sine wave on the scope, from the RF 
pickup, while running 1500 watts DC input ?  If so, please send me an email 
at kenw2dtc at comcast.net


The reason I ask is:  A.  None of my amps has ever been that good and B. 
Unfortunately, a number of people running AM linears do not have scopes and 
if you tell them that a pair of whatever tubes can achieve a certain carrier 
power, they will put the carrier to that level via dipping and peaking the 
pi-net until their wattmeter reaches the specified power and talk.  In my 
experience, by the time you heavily load the output to achieve the perfect 
audio sine wave, your tuning controls are quite different than what is was 
when you peaked everything and the efficiency is no longer as good as what 
the calculations show.  On top of that most male voices have peaks that 
should have an additional de-rating of output power.

So when someone asks about what kind of carrier power a certain pair of 
tubes can put out in AM linear service, I really like to give a conservative 
number, not the math numbers.

73,
Ken W2DTC



______________________________________
Ken Barber  Middletown, NJ
Radio Website: http://w2dtc.com
Family Photos:  http://kenw2dtc.home.comcast.net
______________________________________


----- Original Message ----- 
From: "Jim candela" <jcandela at prodigy.net>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Thursday, March 16, 2006 7:22 PM
Subject: RE: [AMRadio] Amplifier to use with my DX-60


>
> Don,
>
>   You said: "So you could run maximum 1500 watts DC input to those tubes,
> with 500 watts
> carrier output, and 1000 watts dissipated by the tubes".
>
> Reply from Jim WD5JKO:
>
>   What is stated above is correct if the tubes can dissipate 1000 watts of
> heat (like two 3-500Z's flat out blushing), and the drive is adjusted to
> about 1/4th that for maximum PEP output. In this case the efficiency is
> assummed to be about 33%, so 1500 X .333 = 500 watts. The efficiency may
> vary some, and is usually lower then that, so the 33% assumption is only a
> first guess. It could be 25%, and that really upsets the situation making
> the linear more of a heater, and less of a transmitter.
>
>   One good thing about the 1500 watt PEP output power rule we all complain
> about is that efficiency doesn't matter as much now. You can legally run a
> 15 KW PEP input amplifier with 10% efficiency to provide 1500 watts PEP
> output. It wouldn't make a lot of sense, or be practical, but it's now
> legal. Back in the 1000 watts DC input days things were a lot different, 
> and
> the SB-220's input would likely exceed 1000 watts DC before the AM carrier
> got to 375 like we often do today with these amps. The point here is that
> for low efficiency linears, or grid modulated amplifiers,  we can 
> sometimes
> run more power today on AM then before the rules changed from 1000 watts 
> DC
> input to 1500 watts PEP output. Of course this isn't the case with plate
> modulation where an output PEP at or maybe more than 3KW PEP WAS possible,
> and completely legal.
>
> Regards,
> Jim
> WD5JKO
>
>
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net]On Behalf Of kenw2dtc
> Sent: Thursday, March 16, 2006 4:21 PM
> To: Discussion of AM Radio
> Subject: Re: [AMRadio] Amplifier to use with my DX-60
>
>
> Don says:
>
> "So you could run maximum 1500 watts DC input to those tubes, with 500 
> watts
> carrier output, and 1000 watts dissipated by the tubes"
>
> *******I need a little help with the math here Don.  You are suggesting 
> that
> with a class B linear in AM mode, one can get 2000 watts PEP with 1500 
> watts
> input ?
>
> 73,
> Ken W2DTC
>
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