Homemade Valve Vacuum Tube Tester Build - Part 2 

Be aware that the toroidal bolt in my build is insulated at the other end so that there is no risk of earthing both ends. If the bolt is earthed at both ends, then it will behave a s single turn winding. Although the volts will be low, the current will be high in the short circuit. This can damage the transformer.

Thank you for showing us this project. Putting it in a camera case is a bit of genius, it looks very smart. I have used this voltage multiplier supply for a valve radio project. Because the current draw is about 60ma I used 220uf capacitors, which gave around 250v under load. I also realised that this a potentially lethal supply. There is a large amount of capacitance,, which holds several joules and stays there for a long time after switching off. so I put bleeder resistors across each stage of the multiplier , the voltage drops away quickly after the power is switched off. It is easy to drop one’s guard after the power is switched off.

Sometimes the cost is not relevant, its the journey, learning and satisfaction at the end that's key.

This is a great reference desin for a Valve/Tube tester. I would probably make a small addition to make a variable voltage on both high voltage and heater so it can test a wider range of valves/tubes, but that's mainly because I do have a wider range of voltages needed for testing what I work with. I think this is an invaluable tool and also a great project for anyone interested in getting into the valve/tube equipment hobby or even for more major restoration work.

your final comments were eye opening that some people would ask about ht options they should stop and only use low voltage eg less than 12 volts or lower

Wow!!! Great circuit and superb build!

Great project, very professional, and always leaves new possibilities to add new features to enhance it. Deeply appreciate your generosity to share it with all. My respects from PR.

I think the build quality is excellent. Nice touch with the aluminium case - looks a bit better than the original Lamington tin!

Tidy build! I've shared your channel with a few Facebook groups.

Well done!

Parabéns amigo! Estou esperando mais vídeos! Também gostaria de fabricar um testador de válvulas até porque tenho um rádio de válvulas para arranjar e só agora com 64 anos estou a estudar verdadeiramente as válvulas e ainda quero construir um amplificador de válvulas foi sempre o meu sonho ter um .

Nice project. However, I would make some comments regarding safety. Firstly, when measuring continuity to ensure all of the metal parts in the case are connected, the standard is to use a continuity tester with 100mA test current. An ordinary multimeter will have a continuity current of only a few mA. Secondly, It is considered very bad practice to use the mounting bolt for a toroidal transformer as an earth point. If you accidentally earth the bottom of the bolt, you will create a shorted turn on your transformer which will in turn make a big bang. Thirdly, I suspect the push switch you are using for the gas test is not rated for a sufficiently high voltage to be safe (and indeed your toggle switches may only be rated at 125V - you should check). Finally, when making this kind of circuit, you really need to have a high quality multimeter with at minimum a CAT I rating and preferably CATII or CATIII. They are not super expensive and I recommend the Brymen BM235 as an excellent meter for less than £100. Also, (and this is just a personal view), I would have wired the grid voltage potentiometer the other way as the convention is to turn a knob anti-clockwise to make the situation 'safer'. Good luck with your new channel.

As far as I know, the most important parameter of a valve, is the condition of the heated cathode. Only examining the state of the cathode can we decide whether a valve is rather new or used or heavily used. This should be the first stage of valve testing and everything else should come after that. And you can check the condition of the cathode is pretty easy by measuring the emission current at two points. One point at nominal heating voltage and an another at 60% of the nominal heating voltage. If the emission current does not drop below 50%, than the valve is good, if it drops below 10%-50% then the valve can be usable, below 10% percent it is bad.

pretty nice build there, I think you could also opt for a high voltage booster if you want to save on the doubler caps. I have a real tube tester but I kinda want to build something like the one you have here but as a kind of amplifier instead so you could actually play music with the tubes under test to see how they actually sound in circuit. I think it could be a very useful thing to have if you want to re-purpose non audio designed tubes for audio anyway to see how they perform as this. I have a ton of tubes but if you don´t know how they sound it is hard to do a good design around them

Nice work ! Hope to see more videos like these two soon.

It'd be funny to have a microcontroller in there to do the tests automatically and the transconductance calculations.... and It'd be even more delightfully anachronistic than the optocouplers would have been. ;)

Nice job 🙂

Nice Video. I actually have built my own based on the same reference design. But not looking as good as yours... So far i have used a variac for the AC input to fine tune voltages. Not used high/low voltage selector som far. Considering a seperate bias voltage supply to keep it stable when i adjust tha variac. Maybe you would like to make a video covering testing common valves like EL84/EL34/ECC83/5881/6V6/6L6 ?

Thanks for the video.The idea of using a voltage doubler is great although this provides limited available current, but you probably have enough to power the tubes you use.I also noticed that you didn't use any method to stabilize the anode voltage, so I'm wondering if you can maintain a good balance with power tubes that require hight current.To measure gm no declared anode voltage is required, therefore it is possible to carry out the measurement at any operating point, but during the variation of g1 the anode voltage must remain constant for an accurate measurement of gm.

Nice job 🙂 Witch program do you use to draw stripboard and panel design

Fantastic. How about a design for DHT valves?