Home brew liner

[K3ZW]

Hi all. I have assembled a linear amplifier bassed on W6SAI's four 811A design in the Radio handbook, I intend to use 572B's
I havent done this sort of thing in many years and I need to be refreshed on  the difference I should see between input power ( calculate) and output power ( wattmeter) so I know things are working correctly.

I havent purchased a new set of 572B's yet. I tested the amp with a couple of old Cetron 572B's I had laying around. I was able to load the amp up to about 340 watt DC input on 3.5 MHz 1650V was the plate supply voltage under load.

Any coments or advice would be apreciated.

Thanks

Paul

[wa3dsp]

Sounds like an interesting project. You can run much higher voltages on the 572's. The Heath SB200 runs two at around 2200 volts and gets 600 watts or so out on 75 meters. You should be able to get 1KW out of 4 tubes unless you want to run more conservatively. Use some protection in the plate supply - fuse and a resistor. Typically 10-15 ohms 10W and an appropriate fuse insulated for the plate voltage. Also it goes without saying be real careful around these voltages. They are lethal.

In one of the Heath SB200 mod pages there was a note about testing the 572's. I think I have it somewhere. The guy tied the grid and plate together, lit the filaments and applied about 40-50 volts DC plate to cathode. I think the current was about 240-250ma for a good tube. This is also a good way to burn new tubes in. You should run the filaments for several hours on a new tube before applying DC.

You might want to google 'Heath SB200 mods' for reference.

73 Doug

[kb3ouk]

For AM, you don't want to run more than about 500 watts of carrier with them. I have a Hunter 2000B that uses 4 of them with 2000 volts on the plate, and it will easily do 200 to 250 watts ouput.

[Steve - K4HX]

AB linears run at about 60% peak efficiency. You can see more or less depending on the band, the condition of the tubes and the amount of loading.

... the difference I should see between input power ( calculate) and output power ( wattmeter)

[K3ZW]

Funny you should mention the Hunter 2000B. My power supply has the 2000B transformer and pretty much a copy of their doubler circuit. Many years ago I parted out a 2000B & a Gonset 201. This is why I am using the 572B.

 At this time I only have 120V for power because I live in an old rented home. So I have to run the linear at reduced power. I do intend to use the amp on AM so I want to be nice and gentle.

I am using a Ranger transmitter at this time for testing. I am driving the amp with no input tuning circuit. The ranger's tank circiut is very versitile and couples up nicely. I will have to whip up some input tuning when I test on SSB as my SSB rig is solid state.

[kb3ouk]

I run my 2000B off of a 120v line, other than the fact that the lights do dim a little bit when I'm running full power, it does fine. I think it runs about 400 milliamps of plate current at 2000 volts.