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Author Topic: 572B grid current rating  (Read 608 times)
KM1H
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Posts: 5516




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« Reply #15 on: October 12, 2019, 09:11:21 AM »

Quote
There is a slight blue glow just inside the envelope that does not change with plate current. I assume it's just an impurity in the glass, not gas.

While that may be so with many receiving tubes:

Shuguang 572B tubes have a long history of not pumping down the vacuum fully to absorb all remaining gases. The graphite anode versions should be run to reach a moderate red color once in awhile to regetter.
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K7RJB
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« Reply #16 on: October 12, 2019, 11:59:38 AM »

Is it that or is it leaky sealing of the pins?
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KM1H
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« Reply #17 on: October 12, 2019, 05:35:38 PM »

Is it that or is it leaky sealing of the pins?

There is a HUGE difference between internal gas and air seal leakage; many seem to not understand the difference no matter how many times it is covered. The latter will result in an instant filament flash and destruction upon filament voltage application....no HV required. It also includes the plate cap.

Carl
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N8FVJ
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« Reply #18 on: Today at 02:40:47 AM »

Running my AL-811 amp with DX Engineering 572B tubes at 50 mA/tube grid current it'll output 500 watts key down on 80, 30 and 20 meters and 400 watts on 15 and 10 meters. Running 65 mA/tube (~30 mA/tube average) in OOK CW it'll output 600 watts on most bands.
Operating my AL-811 with NOS Cetron 572B tubes I have about 40 ma Grid current for all three tubes with 800 watts PEP out. Meter is slow so actual peak grid current is estimated at 80 ma for three tubes or less than 30 ma per tube.
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