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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 7th Jun 2021, 4:33 pm   #21
Radio Wrangler
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Default Re: Odd gm readings when testing valves. Maybe 42 isn't the answer to this one?

I'm not sure the term 'super valve' is appropriate. I suspect they're on the way to being crappy thyratrons.

David
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Old 7th Jun 2021, 4:41 pm   #22
ms660
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Default Re: Odd gm readings when testing valves. Maybe 42 isn't the answer to this one?

Quote:
Originally Posted by thevalveset View Post
Now to the second valve, the TH233
Triode section should give an Ia of 4mA @ 0V grid, it gave Ia=20mA
If that's at Va = 100 volts then 20mA is low according to the manufactures valve data.

Lawrence.
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Old 7th Jun 2021, 4:56 pm   #23
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Default Re: Odd gm readings when testing valves. Maybe 42 isn't the answer to this one?

Where did you get the test figures for the TH233?
These are the AVO test which uses AC:
Triode Va=100, Vg=-2, Ia=4mA
Hexode Va=150, Vs=100, Vg=-2, Ia=2.6mA

The Mullard HSVT which tests under DC conditions:
Triode Va=98.81, Vg=-5.31, Ia=2.5mA minimum, typical 5mA
Hexode Va=98.65, Vs=100.04, Vg=-3.04, Ia=3.35mA minimum, typical 6.7mA

The AVO uses AC for testing and the figures are what to expect from an AVO and may not match the valve specification, http://www.r-type.org/pdfs/th2321.pdf.
The HSVT uses DC so should reflect the specification. The figures here are created from my emulator as the instrument only shows red/amber/green.
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Old 8th Jun 2021, 6:32 am   #24
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Default Re: Odd gm readings when testing valves. Maybe 42 isn't the answer to this one?

I've had this too with 807's and other OP valves, the odd one tests way over spec for emission but responds as per normal.

Andy.
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