[Amps] While you're on the subject of Alpha 77SX...

[Steve Bookout]

Hello all,

I've got a very late model, pristine, Alpha 77DX/SX, which was 
originally a DX model.  The modification looks 'factory', because, I 
assume, someone used the factory parts.

Don't know it's history but when I got it there was a problem in the 
start-up timing circuit, which I found and fixed.

My question for the group.

In order to make 1500 watts output, I have to drive the amp to .95 
amps/3600 volts and 100 ma of grid current.  My first thought was soft 
tubes, but it only takes 22 watts of drive to get the 1500 watts out.  
If this was one of my home brew amps, I would think the taps were off.  
BTW, this is only on 40 meters where the amp is currently being used.  
That's 3420 watts input for 1500 watts output.

Anyone want to take a guess why it's so inefficient?

Had one amp I got from an estate, an AL-1200 that had a worn out 
tube.    Took 700 ma plate @ what ever the plate voltage was and 250 ma 
grid current to make 1400 watts out.   And, it took about 100 watts of 
drive to do it.  Max plate current, max grid current and max drive for 
1400 watts to me equals a worn out tube.

The Alpha is similar with only 22 watts of drive.   And, yes, I know the 
manual says I can use up to .300 ma of grid current, but not going there.

73 de Steve, NR4M