[HomeBrew] 6v6's modulating a 6L6?

[N2EY@aol.com]

In a message dated 7/18/2003 12:23:22 PM Eastern Standard Time, catman351@yahoo.com writes:

>I have that Heathkit AT-1 that runs about 10-12 watts out/24-35 watts input (that's a pretty big drop from input to output power!)

The AT-1 design really isn't very good, even for its time. There was an article in QST in the mid-50s which showed how to radically improve the AT-1 with only a few parts. The QST index lookup should have it. I think the article was by W1ICP.

> and a Muzak p-p 6V6 amplifier that is supposed to run around 8 or so watts out. Something tells me I may be running a little shy of 100% mod mark if all I need is 50% of the input power (i,e 12-17 watts of the Heath's input power and all I'm running is 8 watts on the Muzak). 

Yep. If the 6L6 is running 30 watts in you need at least 15 watts of audio to get 100% modulation. A little more is better so the modulator won't have to work so hard. Also, you will need a matching transformer between the Muzak and the AT-1, which will have its own losses.

>Otherwise, I think it might have been a cute setup to AM modulate the AT-1 using the Muzak (and a story for ER). Let me know your thoughts and thanks. 
> 
One solution is to simply run the AT-1 at 15 watts input. But with the terrible efficiency of the stock AT-1, that means an output of maybe 5-6 watts! If you're satisfied with such low power, cathode, grid or screen modulation of a revamped AT-1 will do the job.

Another solution is a homebrew modulator. Maybe a Heising setup if you can locate a suitable choke. 

73 de Jim, N2EY