[Amps] AL1200/RTTY

[Bill, W6WRT]

ORIGINAL MESSAGE:

On Thu, 02 Jul 2009 08:28:40 -0700, Kevin Normoyle <knormoyle at surfnetusa.com>
wrote:

>
>Hey Bill: it does raise the question: When your coil blew, how did you 
>know you were running 1500W?
>If the AL1200 was underreporting (like mine might be), then maybe you 
>were over 1500W??

REPLY:

That was enough years ago that I can't honestly remember, but I was probably
using a Kenwood SWR/Power meter at the time. 

In any event, since I know power meters are notoriously inaccurate as well as
frequency-dependent I always tune up by peaking the tune and load caps for max
output, while limiting the DC plate current to a specific value by adjusting the
amount of drive. For example, I now use both a Bird 43 and a Palstar PM2000A.
They agree pretty well on 20 meters and a bit less well on other bands. I find
my amp puts out exactly 1500 watts on 20 meters when peaked up and with DC plate
current of 800 mA at 2900 VDC. So on other bands, I tune for max output with 800
mA DC and let the output fall where it may. I get a variation of about 50 watts
from band to band with the Bird, somewhat more variation with the Palstar.

I also monitor the blower exhaust temperature to be sure the tube is happy on
all bands, which it is. My blower is a 91 CFM model which is overkill for a
single 8877, so the output temp never goes over about 140 degrees F. On other
commercial maps I have had, it usually hovers around 190 degrees max under high
duty cycle conditions.

Hope this helps.

73, Bill W6WRT