Longhin tube testers

02.11.2011..

The tube tester is a tool of the good old times. When the digital was “unreported”, to use the language of the weather forecasts, as if the sites had disappeared from the geographic map. When you hardly listened to the 78s, not yet the “long playing” records. What pops into my head is the smell of the soldering. Greasy dust on the tall and deep shelves, crowded with the cabinets of electronic devices to be fixed. Or to despoil just to get cheaper components and spares. In short, it was a gear likewise Metropolis by Fritz Lang, between the post-futurist and the nearly-science fiction.

 

The vintage you can find nowadays in the art and craft markets, if properly well preserved and operational, usually does not have any instructions and test tables. The older devices, even if equipped with instructions, cannot test the more recent vacuum tubes, since the test parameters are missing. Our technicians can give some authoritative info, though: we are speaking of “emission” testers, to be more precise. The testers at “mutual conductance”, of more limited historical production, are very rare and do not need tables or calibrations notes. What you need are only the parameters of the tube functioning that is in any manual.

 

Today, owing a modern tube tester is not just an anachronistic luxury, but rather a modern necessity, at least for who, like us, suffers and still spreads the charming of the luminous tubes. I said “modern” on purpose. The old tube testers used to put the tubes under a short-circuit test, to discharge the faulty ones. The run-in should be useful also to eliminate or mark the faulty tubes as second choice, considered that the infant mortality during the first hours of working of the untested tubes, is as much unpredictable as elevate. The fact is that the low costs imposed by the industrial production do not allow deep tests or authentic verifications. Sometimes is more expensive checking out the tube and present it wrapped in a fine package, than make a serious test. Surely, some big manufacturers produce also tubes that have been tested and selected, but with skyrocketed prices. And the service is not always reliable, at least as they promise. I asked sometimes for selected series of tubes and, once tested, I found out they had been matched as I could match with Jennifer Lopez…

 

So, what to do then? You can choose DIY, seeing that several sound designs exist and are not very expensive. You can purchase professional products, for example made in USA, but the rates are high. Let's do this in an orderly fashion with some examples. As pieces of advice, for DIY we can refer to Le Radio di Sophie website (Italian only). For a better technical understanding to ARG-audio website (Italian only), where you can have a look at historical devices and military surplus. Otherwise, we indicate the Longhin tube testers. Modern tools, up to date, smart and sexy, as the cutting-edge technology says today: see Apple. Three models with progressive performances, held into aluminium briefcases, like the ones used by photographers, electricians or professional killers...

 

A couple of words about the author. Paolo Longhin was still a kid when he comes into the world of electronics, tubes and radio transmissions. In 1961, he graduated at the Istituto Radiotecnico A. Beltrami in Milan as radio transmission technician. In his long career, he did many things that have brought him a complete technical-professional background. He has worked in many sectors and for many companies. Together with his son and some partners, he has also provided terrestrial and satellite broadcasting services at the regional RAI in Milan*.

 

The Longhin tube testers are devices that analyse and compare thermionic tubes. Tube testers to verify and compare quickly and with precision the characteristics of preamp and power tubes, included the "magic eye". They analyse and control all the parameters of the tubes with a microprocessor. The parameters of the tube are then visible on an LCD screen. Through the motherboard, the voltage and current values will no more be conditioned by the variation of the network, noises, etc. In this way, it is possible to obtain, from each tube, very reliable parameters for the next selection and match.

 

Tubes are complex devices. To work properly, they involve thermic, electronic, chemical and physical principles of materials and gases, just to quote the main ones. We hope that the Longhin tube testers can be of interest for the enthusiasts of the old radios, for the audiophiles who are sure of the superiority of the tubes, for the amplifiers makers, repair people and hobbyists who need precise and certain data to match their tubes. The prices, moreover, are very interesting if compared with the historical ones or with the more emblazoned current production.

 

Thanks, Paolo. The few square meters of your lab are great as the electronic history, which you may say having lived in first person.

 

 

Official technical specifications:

Tube Tester Lo460 e Lo460TMs

Power supply: 100-120V 50/60Hz / 220-240V 50/60Hz

Adjustable anode voltage: from 2,0 to 450V

Negative grid voltage (BIAS): 0 - (-50)V, ± digit

MAX anode current: 200 mA, with digits to 32 mA

Adjustable filaments voltage: 1.5-61V with digits from 1,2 to 24V 3,5A

Three sectors LCD

Anode and negative grid voltage measurement (bias)

Plate current measurement (anode)

Precision LCD for measurement of the filaments voltage

Tube Tester Lo700

Power supply: on demand100-120V 50/60Hz / 220-240V 50/60Hz

Adjustable anode voltage: from 10 to 700V

Adjustable Grid2 voltage: from zero t 430V

Adjustable negative grid1 voltage (BIAS): positive from 0 to +10V and negative from zero to -100V

Adjustable negative gride3 voltage: from zero to-60V

Adjustable filaments voltage: from 1.2 to 22V with 3,5A / from 20 to 61V with 500 mA

Limited anode current to 280 mA

Onboard sockets (8): Noval, Octal, UX4, UX5, UX6, Miniat.7, Magnoval 9, Decar/Compactron

Measurement method: direct-current managed by processors

Precision: < 2%

Grid voltage resolution: from zero to -40V, 0.1V, digit measurement from -40 to -100V in Volt

Voltage filament resolution: digit measurement

 

Official Italian dealer: to Radiostoria.com website

 

Official current price in Italy: Lo460, 500,00 EUR; Lo460TMs, 650,00 EUR; Lo700, 860,00 EUR

 

RIGHT OF REPLY | MANUFACTURERS FEEDBACK

Ciao ragazzi,

finalmente i miei provavalvole hanno anche un commento coreografico.

Vi ringrazio del lavoro che avete fatto.

Paolo Longhin

03/11/2011


*Unfortunately, he passed away in 2012, but his website is kept alive by one of his collaborators in remembrance.


by Giuseppe Castelli
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