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Old 26th Feb 2014, 6:01 pm   #1
Ian - G4JQT
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Default EF91 and CT160 tester

I'm testing some EF91 valves on a AVO CT160 valve tester.

The EF91 is just a pentode. But the entry in the AVO valve data manual implies this valve has two anodes as the listing shows two negative grid voltages and two anode and screen voltages.

However, none of the roller numbers (412 361 500) are marked 'A2', confirming there is only one anode.

Presumably this double entry is showing that there are two common sets of voltages used for the EF91 and has nothing to do with it actually being two valves in one envelope.

Testing on 'A1' using either sets of voltages was a inconclusive, nothing obviously wrong, but Ia and mA/V a bit low on numerous EF91s tested.

As expected, there is no anode current when the electrode selector is set to 'A2'.

It's unlikely this is a misprint so I'm a bit confused...

I reckon I've missed something I should know about, so comments welcome.

Thanks,

Ian
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Old 26th Feb 2014, 6:23 pm   #2
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Default Re: EF91 and CT160 tester

My manual for the CT160 shows the same switch settings, but all only has one set of test voltages.

Sorry, but I don't know the issue number.
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Old 26th Feb 2014, 6:29 pm   #3
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Default Re: EF91 and CT160 tester

Just checked edition 20. That only has one set of test voltages.
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Old 26th Feb 2014, 7:47 pm   #4
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Default Re: EF91 and CT160 tester

Hi Graham. That's interesting. I have 16th edition 1964, and two (different?) loose-leaf photocopied books of unknown editions.

They all have the following data:

421 361 500

Vf=6; -Vg=2; Va=250; Vscr=250; Ia=10mA; 7.6mA/V

and

Vf=6; -Vg=1.5; Va=200; Vscr=150 Ia=4mA; 6.4mA/V

So it looks like it's been updated after my edition. I can't believe it's a misprint on such a common valve that had been around for more than 10 years before my 1964 edition was published.

I'm sure there's an obvious explanation.

Ian
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Old 26th Feb 2014, 9:20 pm   #5
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Default Re: EF91 and CT160 tester

The first set of figures match both my editions of the valve data manual.

Could it be that the second set of figures were for a different AVO tester? Some editions cover more than one tester.

You can download edition 20, dated 1974, here:-

AVO Valve Data Manual - Edition 20
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Old 26th Feb 2014, 10:56 pm   #6
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Default Re: EF91 and CT160 tester

Thanks for the link to the manual. I have downloaded that and will keep it.

My editions have voltage settings for the CT160 and separate columns for 'data for AVO valve tester' for each valve.

Double valves are {in brackets like this} with separate voltages for each anode, which is just how the EF91 is shown.

Regards,

Ian
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