[AMRadio] AM Amps


Gary Schafer garyschafer at comcast.net
Tue Jan 11 21:03:25 EST 2005


I know full well that there is no such thing as a 375 watt carrier limit 
to AM power in the FCC rules. I never said there was.
I was trying to "clarify" Ronnie's statement about how much power he 
runs his 813's at when he says he runs them at legal power out.

And since we don't know if Ronnie has a symmetrical voice pattern or 
otherwise, we can only assume it is symmetrical when discussing general 
power principles.
Maybe he has the peaks phased so maximum peaks are in the negative 
direction? I don't know. Either way it appears as though he only has 
enough headroom for less than 50% modulation in the positive direction.

On top of that the plate dissipation is around 380 watts per tube if the 
amp is tuned properly, which it can't be if it is not burning up tubes.

That is the whole point, if you are paying attention. :>)

Maybe you could tell us how much peak envelope power would be available 
from a pair of GG 813's at 375 watts carrier out with 100% modulation?

73
Gary  K4FMX


Geoff wrote:
> Gary Schafer wrote:
> 
>> By "legal power out of the 813's" I assume you mean 375 watts carrier?
> 
> 
> Why assume something that is false??
> 
> That statement is -designed- to put you on edge, Gary.  Perhaps it's 
> just my perception, but it simply appears as if you're not paying 
> attention.
> 
> NO WHERE does it say that 375w of carrier is the 'legal' limit.
> 
> The LEGAL limit is 1500w PEP output.  It's just a point of reference, 
> that if you modulate a 375w signal with a sine-wave to 100% audio, then 
> you will reach 1500w pep output.  The truth of the matter is, we don't 
> -speak- in sine-wave.  Our voices are rather asymetrical.  Some of us 
> have voices that are rather 'peaked'.  In order for the audio amplifying 
> equipment to properly modulate 375w of carrier, instead of needing to 
> only be 50% of the carrier, or 187.5w of needed audio, you -might- wind 
> up needing an audio system with the capability of producing upwards of 
> 600w of AUDIO.
> 
> (ref: http://w5omr.shacknet.nu/~wa5bxo/asyam/Amplitude%20Modulation.htm)
> 
> THIS IS NOT TO SAY that you'll be pushing your positive peaks that high, 
> but in order to keep your signal clean, and well within "good 
> engineering practice", you certainly don't want any flat-topping or 
> distortion.  Anything in the audio system that does -not- allow your 
> audio to be clean and free of distortion then, by definition, wouldn't 
> be operating within "good engineering practice".
> 
> 
> 73 = Best Regards,
> -Geoff/W5OMR
> 
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