[AMRadio] AM Amps

Gary Schafer garyschafer at comcast.net
Tue Jan 11 22:50:18 EST 2005

Geoff wrote:
> Gary Schafer wrote:
>> 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.
> Ok, good.  I was just making sure ;)  Too many people believe that 
> there's some 'magical mystification' about 375w of carrier output being 
> the 'legal limit'.
>> 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.
> Agreed, there.  And, I've been to Ronnie's shack.  I'm pretty sure he 
> doesnt' do any audio shaping, or phasing, or any other audio tricks on 
> either the Ranger or the Globe King 500 he's running there.
>> 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. :>)
> I was... it was just the 'legal limit' that caught my attention (yet 
> again ;->)
>> 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?
> I'm not sure you can get more than around 1kW PEP output of a pair of 
> 813's... and probably more like 800w.  (3) in parallel would be a 
> different story, though.
> 73 = Best Regards,
> -Geoff/W5OMR

I would say you are pretty much on the mark there. I have a pair of 
813's in GG also. I only run them at around 2500 volt and can get about 
650 watts max out with 100 watts drive if I remember right.

I ran them well over 3000 volts many years ago and got quite a bit more 
out of them but didn't have a decent watt meter then so I don't know 
1000 watts out seems doable but they will be running around 1600 watts 
or more input. They will turn pretty red. Even on SSB at that power.

Gary  K4FMX

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