Skip, he is reading the grid current wrong!!!!!! ?THE SB200 amp does not have a graduated scale for grid current!!!!!! It only has a white area as a safe zone. ?The last mm of the white zone is 100 ma. ?But it¡¯s NOT on the scale.
On Wednesday, December 20, 2023, 7:03 PM, Steve <k0xp@...> wrote:
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
On 12/20/2023 3:30 PM, NI5L wrote:
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
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