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Old 10th February 2011, 05:27 PM   #1
Reeler is offline Reeler  Spain
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Default Valve testing machine

It is my understanding from my own experiences that in order to make up "matching Pairs" of tubes you need one of these expensive antiquated machines capable of reading the valves values. So many ins, so many types of valves and then to refer to the books.

Is it time for a simple cheap machine to diagnose these valves?
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Old 10th February 2011, 05:45 PM   #2
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Could be make easily, I have some schematics of Neuberger RPM370 and Hickok I-177B if they are useful for you.


Good luck!
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Old 10th February 2011, 06:56 PM   #3
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I have made tube matching ( = selection of equal pairs) without any tester by simply using fixed anode and screen power supply and adjustable G1 negative suppy. I just connect these to the tube socket by jumper wires.

Then I adjust the anode current to typical operating value by means of G1 voltage and simply put all the required tubes in turn in this test installation and take the anode current readings.

Even the Gm could be analyzed/matched with this simple system.
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Old 10th February 2011, 11:16 PM   #4
taj is offline taj
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Geek over at GeeK ZonE GeeKs - Index designed a tube tester that is about half-way between a commercial one, and a simple testing circuit.

But I can't find the thread about it in his forums.

..Todd
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Old 10th February 2011, 11:38 PM   #5
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Quote:
Originally Posted by taj View Post
Geek over at GeeK ZonE GeeKs - Index designed a tube tester that is about half-way between a commercial one, and a simple testing circuit.

But I can't find the thread about it in his forums.

..Todd

Tube tester - on the breadboard.
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Old 11th February 2011, 09:32 AM   #6
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"Sussex" Homebrew Valve Tester

The "Sussex" Homebrew Valve Tester. - UK Vintage Radio Repair and Restoration Discussion Forum
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Old 11th February 2011, 05:38 PM   #7
mogliaa is offline mogliaa  United Kingdom
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If you have access to an XY oscilloscope, you can easily plot the transfer function and compare valves for matching purposes. Have a look at the circuit adapted here:

Valve curve tracer gm tester
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Old 11th February 2011, 08:50 PM   #8
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Quote:
Originally Posted by artosalo View Post
I have made tube matching ( = selection of equal pairs) without any tester by simply using fixed anode and screen power supply and adjustable G1 negative suppy. I just connect these to the tube socket by jumper wires.

Then I adjust the anode current to typical operating value by means of G1 voltage and simply put all the required tubes in turn in this test installation and take the anode current readings.

Even the Gm could be analyzed/matched with this simple system.
This way is probably the easiest and best way to go. If you have lots of time, you can slowly adjust G1 voltage and graph it along with plate current readings. Then you can match up graphs / plots of your group of tubes and get excellent matched pairs / quads, etc.
I have done it this way for years... I usually buy 26-30 tubes of a particular type and manufacturer burn them in for 24 hours and then do the plots of G1 voltage vs. plate current. With this many tubes I usually get several matched quads, several pairs; I have even got an octet once. Most tubes will match; I might get 2 tubes left over that don't match very good with the rest.
And I am talking tight matching... like to within 1%, 2% at most.
Traditionally, matching has meant matching for transconductance only. Groove Tubes changed this for the better.... They matched for both transconductance and current... This is the way to go. With the above equipment you will be able to do this.
Basically what you will need is 2 power supplies... B+ and a negative supply for the G1 voltage. If you want to get fancy, make the voltages regulated. If you want to get real fancy, make the screen (G2) voltage variable also...
And if you want to achieve "tube guru" status... Make the tester all automatic; let it do all the work... You are on your own on that one though....
Daniel

Last edited by danFrank; 11th February 2011 at 08:53 PM.
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Old 15th February 2011, 07:20 AM   #9
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Hi Ale.
Did you go to Tonbrige on Sunday?
Henry
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Old 15th February 2011, 07:37 AM   #10
mogliaa is offline mogliaa  United Kingdom
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Hi Henry, was planning to but couldn't make it. Did you go?

Now I'm in the process o modifying the Sussex VT :-)
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