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Author Topic: AL-811H HV  (Read 4363 times)
N0SQ
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Posts: 53




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« Reply #15 on: May 19, 2012, 08:48:55 AM »

4WS:  Wade, no offense meant, but a screwdrivers isn't a chicken stick!  According to everything I've read for decades shorting HV to ground with a screwdriver or similar device can potentially overstress components in the power supply.

When I was in the military, we were provided with sticks that were tied directly to ground. Anyway, I discussed this issue with a friend that worked on FM broadcast transmitters and he said it's better that you destroy a transmitter component than risk getting yourself killed. Having a resistor between the stick rod and ground isn't the safest course to take. And if you're working with others it's best to use a shorting stick tied directly to ground in case some moron turns on the power to the transmitter while you're working on it. I suppose the best solution is to have 2 sticks, one for discharge and another for a safety stick that's tied directly to ground. But, I plan to use just a stick that's tied directly to ground.
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N0SQ
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Posts: 53




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« Reply #16 on: May 19, 2012, 09:13:16 AM »

If you need a little more info here is a link which explais how it works and how to wire it. http://sound.westhost.com/articles/buck-xfmr.htm#s30

Frank

Thanks. I'll have to see about ordering one before something goes pop.

But, I'm surprised that Ameritron didn't put in higher voltage power supply capacitors in this amp. I was under the impression that the design rule is to rate the capacitors 1.5 times the working voltage. In this case the capacitors should've been rated at least 600 volts each (instead of 450 V) - since the 4 caps are in series this would allow for voltages as high as 2400 VDC across the capacitor string.

However, from what I've read on an 811A spec sheet the maximum plate voltage should be 1500 volts for class AB2 but Ameritron says the HV should be a nominal voltage of 1700V. Oh well, I'm not a design engineer so I don't know what the engineer was thinking when the amp was designed. I should just go buy 572B's and eliminate this issue also. Looks like the 572B can handle 2400V plate voltage - plus I could run RTTY at max amp power with this tube.

But, I'm going to leave things pretty much the same as original - otherwise by the time I get done redesigning/improving the amp I might as well as go buy another amplifier that's "properly" designed.
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K4RVN
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Posts: 757




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« Reply #17 on: May 19, 2012, 09:19:39 AM »

After reading your comments on the resistor, I'll add another and check for continuity before and after I use it. I had never thought about the fact that the resistor could be open so we all can learn from others for sure.
Also you are welcome WX7G.

Frank
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