couple questions for the group: AL-811H, and a biasing method

[K8DI]

Hi folks -
 first:  I've gotten my buddy interested in trying AM. He's had weak luck with his Kenwood barefoot (not unexpected). He has an AL-811H amp. It is in great shape, he is an engineer who loves tube stuff. He has nearly new US made tubes in it.  What is a safe carrier power output level for an unmodified 811H? Consider both the tubes and the power supply.... I know it's supposedly 800 watts PEP, so a 200 watt carrier shouldn't clip/flat-top, but will it burn up the PSU and/or plates?

second: see the attached diagram. Tell me why this would not work in place of a grid leak resistor in a grid-driven plate modulated class c amp stage that has to draw say 10mA grid current (think 4-400A/5D32 kind of level). Assume the 100v is sufficient safety bias in case of loss of drive.  I can't see any reason, but I know I don't know enough to know....

Ed

[Pete, WA2CWA]

What's the exciter? How much power output in the AM mode? Is it adjustable? How about showing us a circuit for the AL-811H to get an idea as to how it's driven. A blank screen doesn't help the readers.

[K8DI]

What's the exciter? How much power output in the AM mode? Is it adjustable? How about showing us a circuit for the AL-811H to get an idea as to how it's driven. A blank screen doesn't help the readers.

Pete, the two questions have nothing to do with each other, except simultaneously occupying my thoughts. I shoulda made two posts. To your questions, the exciter can be assumed to be adequate and adjustable. Mostly what I’m looking at, is instead of a big power resistor and drive changing the current AND voltage, using zeners where as drive is varied, grid current will change but the bias voltage won’t.

Ed

[KD6VXI]

Fixed plenty of AL811H amps for CBers over the years.


The tubes and power supply are both limiting.

It's good for about a hundred watts of carrier.  75 is better if you want high positive peaks.

Remember, it's about 30 to 35 percent efficient at carrier level.

572b will take care of the tube dissipation but does nothing for the small transformer.



--Shane
WP2ASS / ex KD6VXI

[K8DI]

Fixed plenty of AL811H amps for CBers over the years.


The tubes and power supply are both limiting.

It's good for about a hundred watts of carrier.  75 is better if you want high positive peaks.

Remember, it's about 30 to 35 percent efficient at carrier level.

572b will take care of the tube dissipation but does nothing for the small transformer.



--Shane
WP2ASS / ex KD6VXI

Thanks, Shane.  I figured a hundred watts was safe, and more wouldn’t be, but I have no personal experience with anything 811, so I thought I’d ask.

Ed