AVO VCM vs Taylor 45 mutual conductance
 

I am trying to test a PX4 using DC conditions (using a modified Mullard Tester).

The AVO Data says 6mA/V..
The 45 Data says 3.5mA/V.
The Osram Datasheet says 6mA/V.
The Osram Datasheet characteristic chart shows about 4mA/V.
There is a rumour that many of the valve datasheets simply publish the AVO figure.

Measurement is proving difficult on my setup due to the direct heating and even if I used an isolated signal source and anode AC current detector, the HT regulator might mess the value up.

DC gm tests on KT66 come out about right.

Re: AVO VCM vs Taylor 45 mutual inductance
 

Hello,

Using this data sheet :- https://frank.pocnet.net/sheets/126/p/PX4.pdf
The gm of 6mA/V is measured at Va = 100V and Vg = 0V.

Looking at the characteristic curves for Va = 100V:

At Vg = 0V, Ia = 69mA and at Vg = -4V, Ia is about 45mA. which corresponds to a gm of 6mA/V.

However gm does decrease as Vg increases (negatively).

For example at Vg =-8V , Ia= 28mA and at Vg = -12V , Ia = 16mA, which corresponds to a gm of 3mA/V

So the value of gm can depend on the conditions under which it is measured which may well explain the differences between the Avo and Taylor measurements.

Your best bet might be to measure the Va and Vg of your test setup and then use characteristic curves to determine what the gm should be.

Yours, Richard

Re: AVO VCM vs Taylor 45 mutual inductance
 

Richard, thanks as I missed the note where the test conditions were recorded, I had assumed they would match the anode current test conditions. These test conditions would not be a logical choice so maybe the VG=0 is dictated by the way the AVO works with directly heated valves?

Re: AVO VCM vs Taylor 45 mutual conductance
 

They say things happen in ways which overall increase entropy. Typos have a liking for increasing embarrassment. Mutual INductance valve testers, eh?

Fixed

David

Re: AVO VCM vs Taylor 45 mutual conductance
 

Sometimes the brain reads what it expects to be written, not what is written indeed!

I did not notice that typo, had to read it three times!!! But, anyway, Mutual Inductance is a good one, cheerio!

Joe

Re: AVO VCM vs Taylor 45 mutual conductance
 

There are errors in the various generations of AVO valve data books. It isn't surprising when you consider that every single entry was typed by a human.

Both pin connections and some data too. Whenever I get an anomalous result on my AVO3 (or III), I check with manufacturer's data on Frank Philipse's excellent site.

Craig

Re: AVO VCM vs Taylor 45 mutual conductance
 

The manufacturer data sheets are the safest method (for the valve tester), along with the Avo Manuals in conjunction with the base type and number which are in the Wireless World Valve Data manual as there will be errors in that as well no doubt.

The results of the test can be compared from any of the sources. Or at least that is my assumption

Re: AVO VCM vs Taylor 45 mutual conductance
 

Someone with time and money should set up a webpage with measurement results, as well as what equipment and settings they used to get these results, for all valves available so everyone could check their results against those results.

Some sort of comments and vetting would be welcome on such a page too.