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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 19th Nov 2019, 11:55 am   #1
Diabolical Artificer
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Default Testing 813's.

Just tested three 813's with dire results, one tested fair - 80mA, one was terrible @ 20mA, the other surprised me having a SC between anode and g2/screen grid. A bit freaky with crackles and big blue sparks.

Test conditions were anode 1kv, g2 400v, g1 -20v, filaments 10v @ 5A which should give you, looking at the mutual characteristics graph 100mA emission - ish.

Has anyone had a/g2 shorts on these valves before? In all the valves I've tested this is a first. It always grieves me when valves test kaput, the 813 is an especially handsome valve, shame that two are now only useful as display items. Ce la vie.

Andy.
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Old 19th Nov 2019, 12:25 pm   #2
GrimJosef
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Default Re: Testing 813's.

A worst-case accident is that if the valve has been mistreated in the past the screen grid might have been thermally overloaded, or a high-voltage arc to it might have occurred. In either case a grid wire might have snapped. Then an a-g2 short is perfectly possible. Can you measure a cold short between them now just using a meter ? If you lay the valve on its side and tap it does any debris collect at the bottom of the glass ?

Cheers,

GJ
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Old 19th Nov 2019, 1:59 pm   #3
Diabolical Artificer
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Default Re: Testing 813's.

There's no measurable short, however there is some debris, looks like small silver coloured flakes in the valve when it's on its side now you come to mention it. Tapping the valve changes nothing.

Andy.
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Old 19th Nov 2019, 2:35 pm   #4
Andrew B
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Default Re: Testing 813's.

R.I.P. sweet 813, mainstay of so many amateur linears
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