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Something doesn't sound right... you shouldn't be able to get 500 mils grid current and still have working tubes, ESPECIALLY with only 18 watts drive... That's a RIDICULOUSLY-LOW amount of drive; most of us are proud to get 650 mA plate current from a pair of new 572Bs with 65 watts drive power on the HF bands! For the most part, follow the Heath SB200 manual tuning instructions; except that you will undoubtedly find you get much more output power by peaking the plate tuning rather than dipping the plate.

Try increasing the loading capacitance to reduce the grid current below half-scale, as you peak output with the plate tuning. SLOWLY increase drive, keeping grid current at or below half-scale, increasing loading slightly again (grid current should decrease slightly as you increase loading capacitance), then peaking output power with the plate tuning.

My guess is you aren't reading the grid meter right; I can't believe Carl would have messed up the grid current meter scale that badly. Let's put it this way for now... keep the grid current reading below about half scale on the grid meter, whatever that may be.

You can increase drive until the output does not also increase but by then, you may be running the tubes real hard. I'd keep them down to no more than 700 watts output under "rare DX pileup" conditions, and more like 600 watts when working common schtuff like North Carolina or Arkansas. For Nieu Yawk/Nieu Joisey/Pennsy, I'd turn the amp off? 8-D

73,

Steve K0XP

OK. Thanks for the replies, guys. I am getting 600 watts out at 18 watts of drive with the load backed off CCW ~25 watts from peak (per the instructions). The grid current is at 500 mA. The plate current is 650 mA.

Are these acceptable numbers to help the tubes live longer???

Thanks for any input.

Warren / NI5L