Tube tester

I had this itch. Since I fell in love with tubes I have built myself a small collection. New ones and old tubes, sometimes used stock. I have bought the old types trusting that the selling party is honest and measures correctly. I assumed that the new ones are good. But I kept this itch. I just wanted to know how good the tubes match their specifications. Divers investigations on the web came up with tube testers mostly old and used. Some very old, ex army types, expensive AVO testers, a lot of USA stuff for 110 Volt only. I did not dare to buy one. Calling “help” to friends gave either odd looks or a rejection stating: “I don’t know and can’t help you”. No one could help and I became more and more insecure. I was convinced at least two new tubes were far from matched, but could not prove it. Changing tubes from left to right position moved the stereo stage accordingly. But why? A friend suggested to pay half the amount of money involved and share a device. But which tube tester to buy?

In the mean time I discovered a tube tester in the UK, affordable, for small double triodes, under the name Tube IMP mini TT. No old stuff but recently developed and brought to production. Not for power tubes, just for ECC81/82/83/85/86/88 and a lot of equivalents. Double triodes with B9A connector. More then enough for my EAR, Lua and PrimaLuna amps. Although not usable for my 5687 tubes in an Ayon amp, they are not compatible. I am sure a lot of amps use ECC81/82/83 en/of ECC88/6922. Think of Audio Research and a lot of Chinese amps and players. I still had my doubt because I also have KT-88, EL34 and 300B on my wish list. A visit to Hanze Hifi in Zwolle (NL) removed my last bit of worries. I talked to Jaap Pees about my dilemma and he told me that measuring power tubes, especially 300B types is not easy. Separate from his AVO he has a special test bench for single ended triodes. Beside that he was familiar with the Tube IMP and suggested that if I really wanted a tube tester, buy the Tube IMP. Although at the time not available in the Netherlands.

Transferred money to the UK and waited. After I received the tube tester I wondered: “What do I measure and how to read the figures?”. A friend of mine came up with the answers. “What you need is a datasheet with tube specifications. You will find those papers on web sites of amateurs or manufacturers. Look at the graphics and it will be easy. Choose a voltage, a negative voltage on the grid, the heather voltage and measure the tube in the socket”. With the switch you choose the outcome displayed on the Tube IMP. The gain, transconductance of the tube in mA/V or the current in mA. Use the toggle switch to compare the left and right tube half. The way to check that both halves are equal. My friend gave some more info: “The gain will seldom be 100%, mostly around 90% even with new tubes. It doesn’t matter as long as both sides are almost equal. The transconductance should be over 50% of the specified value. Otherwise the tube is end of life. Current should be compared with the data sheet and both halves should be about the same”. Armed with this knowledge and a box of tubes I started measuring.

My wife had a lot of fun, an evening long she heard me mumble: “I got it”, “Measures very well indeed”, “Funny, this old tube is near perfect, this new one is not”, “Oh that old and so good”. No time to have a drink, look around or do something else. At the end of the night I reached the non scientific conclusion that old stock tube are far better then recently made tubes. Second conclusion, the second hand bought tubes are near perfect on both triode halves and measure very well. What I am going to do is open every amp and player around and match the tubes. As my friend said: “Tubes are matched when they leave the factory or before they are installed, but tubes will suffer from using and no one matches tubes during their lifespan.” Right he is, but I have got my Tube IMP and I am able to test the tubes every 3 to 6 months. More is overdone and neurotic. Tubes do not live forever but these small signal tubes do live long. I will be in time to look for replacements if I ever need them.

Enthusiasm comes up whenever I lay my hands on a product that is a. nowhere else for sale, b. works perfect, c. affordable and d. gives many hours of pleasure. So I emailed my friends. High Fidelity Discs called and asked for more information. The result is that the Tube IMP Mini TT will be on sale in their web shop in due course. No longer any need to transfer money to the UK if you don’t like that. No shipping risk and less shipping cost. Buy the same machine in the Netherlands from an already familiar address. No longer screening the web with the insecurity that old tube tester measure false, just tell you good or bad on the basis of only current flow. In the worst case electrocute you or set the house on fire. Maybe I drift off to far, but without extensive knowledge of tubes and testers I was afraid of it. Not with the Tube IMP. I see what I measure, know what I measure en compare my tubes till I find the best sounding, matching and best measuring tubes for my system. Feel secure on buying second hand tubes. I do offer a nice service to friends and colleague reviewers. It is an extension of my hobby and the itching has changed from insecure to very happy. The Tube IMP Mini TT is very useful en fun. You know where to get it in the Netherlands. Not just for us amateurs, also for trade to help customers even better for such a small investment.

Best regards,

Rene van Es