Lampizator's  small tube tester.

A One Evening Project for Novice.

why tube tester?
Because it saves time an money.
There are two types of tube auctions on ebay- expensive auctions for guaranteed tested matched tubes and the "lemon" auctions, when we also pay a lot, or sometimes very little - for unknown tubes.
I like to hunt bargains and special deals - buying lots, bags, boxes, died radio repair uncle stocks etc.

Thanks to my tube tester for example I discovered that ALL of my super  brand tubes are rather bad. If say there is an auction for a pair of Siemens NOS but WITHOUT the guarantee of measurements and matching - chances that the seller of such specialized item does not know what he is selling are ZERO! He is knowingly selling a pair, which is imperfect and he does not claim it is perfect.

The chances of getting a 30 or 50 % different halves in a tube are 95% if the auction is not clearly declared as mint and measured.

I bought recently a box of 100 Soviet military 6H6P's and they were slightly used, not measured and not guaranteed. I paid relatively good price. I was sure they are so so at best. Wrong. I measured that lot of 100 and 4 were 35% off the perfect measurement , but 96 were GREAT . That's shocking good result. But again - the Soviet quality standards were extremely high ( I mean for the goods they cared about - not for consumer goods ;-)

If you use SRPP like me, the good thing is that the two halves do not need to be exactly equal - SRPP takes care of these small differences, but it is important to have similar difference in both channels.
So from my lot I first picked the exact perfect  pairs, say a 16/16 and 16/16, and 17,5/17,5 with 17,5/17,5. That is my premium collection (about 20 pairs from my lot. They will end up in my Fikus DAC)

Then the second sort - also very good for SRPP - is like two tubes similarly imperfect: 15/17 and 15/17.  or 18/16 and 18/16. These will be good for the circuit,  no problemo. I reject things like 12/20 etc.

Of course for anode follower schemes - a perfect balance is more important.

I installed a pot that sets the bias - so we can trace the whole tube curve - say from 0 V to -4,5V bias - the whole practical range for the purpose like lampizator.

I connected in parallel 3 sockets: octal, noval 1 and noval 2, being heated by pins 4-5 or 4/5-9 respectively.

All 3 sockets have triode one paralleled fully (Grid, cathode-grounded and anode supply) and triode2 also paralleled all three sockets.

My V meters show voltage drop on the anode current limiting resistors.

My resistors are 2K and voltmeters are 20 V so the full scale means 10 mA.
Of course we could add more resistor choices and have a switch - selector. Like being able to choose 0,5K, 1K, 2K, 5K  to be able to use the tester for many different tube types. The smallest current expected from a certain tube is 1 mA, the largest is 40 mA in the practical life.

It would be nice to add a third meter - for bias voltage, but we can use our DMM meter here - everybody has one, right ?

tube tester

Tube tester in detail

Oh I forgot to draw the pot. It connects between the AAA cell stack - negative and the ground. The viper goes to tube grid. We also need interrupting switch because the pot (100K or 50K) will discharge the cells.

Of course instead of cells we can build own electronic supply of variable voltage from minus 5V DC  to 0V.

You can buy the kit in our Lampizator Shop

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