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.
Thank you for the feedback. I hope I stressed safety enough in the videos. I have a strict procedure for connecting, powering and disconnecting, and that is for me using it. You really need to be respectful of what this can do to you. I do have a bleed resister in the voltage doubler.
Totally agree. I am really proud of this build and it gets used most days. Same with the old radios I repair. The money and time I put into those far exceeds their monetary value, but I love working on them.
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
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.
Totally agree. You can use an external variable heater supply by connecting directly into the banana plugs to the valve. I am also making an external PSU to vary the screen volage to a much wider range. The limitation of this design is the variable in possible voltage combinations.
I think I will just use my variac on the ac input to lower the output for plate and screen to exactly what I need. With an external heater supply. Not very portable but I don't need to move it from my workshop.
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.
That's a very good idea to enhance the features. We start planning , then making charges to improve the prototype...that's it's evolution of the first idea until we reach our personal needs. Again, thank you for sharing, it really looks great!
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.
Thank you for the comments. Good point about earthing the centre bolt of the toroidal. I will place an annotation in the video and add a comment to the description, along with disconnecting the earth. The bolt in this project cannot be earthed at both ends. The transformer is bolted to a plywood base and that is fixed to the plastic base of the case via wooden standoffs. No metal mounting. There is a cavity between the underside of the plywood and the case. The bolt is confined in that cavity and no wires or metal exist in the cavity. The case has no holes drilled into it so the bolt and everything else is well insulated from the anything outside. I do have other multi-meters. CAT III to CAT IV. I have used them in this video but tend to go for my old academy meter. That too is CAT III. The CAT IV I have is good. I will certainly invest in a good continuity tester. The push switch is 250V 0.5A. Toggle switches are 250V, 3A. That is top end for my voltage and current draw tends to be no more then 30mA max. I have thought about wiring the grid pot the other way round for the reasons suggested by you I will do this when I remove the toroidal earth.
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 .
I am glad you liked the videos. It's really not hard to build a tube tester so go for it. I will experiment with audio valves from TVs as they are very cheap and easy to work with. I have set aside some PCL82 valves that are a pre-amp and power amp in one envelope. I will put up a video of the build. I just need to find the time to start.
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
@@VintageandReclaimedElect yep. I have it on my to do list. I am not completely sure how to best implement and do it yet. The amplifiers I have built so far have a very wide range of compatible tubes already but I want to make it easy to change pinout and everything and that could be the hardest part I think. Bias can be made with a rheostat
Thank you for that. I do have videos planned. I need to add to my test kit with a current limiter, valve rectifier tester and shield voltage/heater supply. I have 4 valve radios to work on, plus some ideas for a valve amp using TV valves. It's just fining the time.
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. ;)
Thanks for that I was just in bed when I saw your comment and that sent my mind running. Those testers are out there. A current sensor for the Anode current. The voltage controlled pot for the grid voltage. Some solid state relays to switch in and out the screen and plate voltages. Gas test needs a current sensor and relay. Shorts test needs a current sensor. An Arduino board could handle all that. You will need a database of valves to set the correct voltage min max levels and a display for the results. Alas, for the time being, I will be to busy building add-ons for this unit to make it more useful than kit is now.
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.
Thank you for your comment. I really appreciate this sort of engagement. It helps all that watch these videos. I have a 50VA transformer at the heart of this and so I believe the voltage doubler will support about 250mA @250V. The most I have seen my valves draw is 36mA. There are many examples of this design on Grant’s web page and some do have an extra meter to monitor the Anode voltage. I saw no fluctuation when I had a meter connected throughout the prototype stage, but I have to say I am working blind as I omitted one in the final build. I do not plan to add any stabilisation. However, voltages are patched through to the valve using banana leads so I could modify the leads and be able to connect a voltmeter through those and manually assess how stable the voltage is.
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 ?
Is there any reason why you couldn't get rid of all that voltage doubler circuitry and use a 1:1 isolation transformer and a couple of small variacs to set the screen and anode voltages? That would give much more flexibility.
You could do that. It is a valid approach. The point about this design is that it is cheap. Costs of an insolation transformer and variacs could be higher. You will also need to rectify the output and make a negative voltage for the grid. The voltage double circularly is not too great anyway. That said I am think about a variac based plug-in module for the screen voltage. At least my final build has the ability to plug in power modules for screen and heater.
We need to be cautious about placing links in TH-cam comments. Just search for LED panel meters and you will see many options. I'm glad you are taking on the project.
Any 12-0-12 50VA transformer will do. You can go to 15-0-15 if you want a 300V+ plate voltage. The heater transformer is a 6-0-6 30VA component. I connected the secondaries in parallel to provide more current capacity. For the meter supplies, I used generic 5V 5A output, AC110/220V to DC5V 25W Universal Regulated Switching Power supplies. These can be easily found on Amazon or eBay etc.
This will work with DHT valves. One side of the heater connection is grounded, effectively connected to the Cathode. The filament voltage can be applied to the other heater connection.
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.
Thank you for the feedback. I hope I stressed safety enough in the videos. I have a strict procedure for connecting, powering and disconnecting, and that is for me using it. You really need to be respectful of what this can do to you. I do have a bleed resister in the voltage doubler.
Sometimes the cost is not relevant, its the journey, learning and satisfaction at the end that's key.
Totally agree. I am really proud of this build and it gets used most days. Same with the old radios I repair. The money and time I put into those far exceeds their monetary value, but I love working on them.
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
Yes, some knowledge is needed here and lots of respect.
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.
Totally agree. You can use an external variable heater supply by connecting directly into the banana plugs to the valve. I am also making an external PSU to vary the screen volage to a much wider range. The limitation of this design is the variable in possible voltage combinations.
I think I will just use my variac on the ac input to lower the output for plate and screen to exactly what I need. With an external heater supply. Not very portable but I don't need to move it from my workshop.
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.
Thank you for the kind comment. I do plan to design a module for this tester in the new year to address some of the short comings
That's a very good idea to enhance the features. We start planning , then making charges to improve the prototype...that's it's evolution of the first idea until we reach our personal needs. Again, thank you for sharing, it really looks great!
I think the build quality is excellent. Nice touch with the aluminium case - looks a bit better than the original Lamington tin!
Thank you for that. It's very serviceable too after I took it apart for an inspection after a valve failed with a bang whilst testing.
Wow!!! Great circuit and superb build!
Thank you very much.
Tidy build! I've shared your channel with a few Facebook groups.
Thank you very. That is much appreciated.
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.
Thank you for the comments. Good point about earthing the centre bolt of the toroidal. I will place an annotation in the video and add a comment to the description, along with disconnecting the earth. The bolt in this project cannot be earthed at both ends. The transformer is bolted to a plywood base and that is fixed to the plastic base of the case via wooden standoffs. No metal mounting. There is a cavity between the underside of the plywood and the case. The bolt is confined in that cavity and no wires or metal exist in the cavity. The case has no holes drilled into it so the bolt and everything else is well insulated from the anything outside.
I do have other multi-meters. CAT III to CAT IV. I have used them in this video but tend to go for my old academy meter. That too is CAT III. The CAT IV I have is good. I will certainly invest in a good continuity tester.
The push switch is 250V 0.5A. Toggle switches are 250V, 3A. That is top end for my voltage and current draw tends to be no more then 30mA max.
I have thought about wiring the grid pot the other way round for the reasons suggested by you I will do this when I remove the toroidal earth.
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 .
I am glad you liked the videos. It's really not hard to build a tube tester so go for it. I will experiment with audio valves from TVs as they are very cheap and easy to work with. I have set aside some PCL82 valves that are a pre-amp and power amp in one envelope. I will put up a video of the build. I just need to find the time to start.
Well done!
Thank you
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.
That looks to be good advice. I can perform this sort of testing with this tester. I give it a try. Thank you.
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
I love your thinking. I will be looking at finding new applications for redundant TV valves.
@@VintageandReclaimedElect yep. I have it on my to do list. I am not completely sure how to best implement and do it yet. The amplifiers I have built so far have a very wide range of compatible tubes already but I want to make it easy to change pinout and everything and that could be the hardest part I think. Bias can be made with a rheostat
Nice work ! Hope to see more videos like these two soon.
Thank you for that. I do have videos planned. I need to add to my test kit with a current limiter, valve rectifier tester and shield voltage/heater supply. I have 4 valve radios to work on, plus some ideas for a valve amp using TV valves. It's just fining the time.
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. ;)
Thanks for that I was just in bed when I saw your comment and that sent my mind running. Those testers are out there. A current sensor for the Anode current. The voltage controlled pot for the grid voltage. Some solid state relays to switch in and out the screen and plate voltages. Gas test needs a current sensor and relay. Shorts test needs a current sensor. An Arduino board could handle all that. You will need a database of valves to set the correct voltage min max levels and a display for the results.
Alas, for the time being, I will be to busy building add-ons for this unit to make it more useful than kit is now.
@@VintageandReclaimedElect I've always got more projects on my TODO list than I've possibly got time to start, let alone complete. ;)
Nice job 🙂
Thank you very much
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.
Thank you for your comment. I really appreciate this sort of engagement. It helps all that watch these videos. I have a 50VA transformer at the heart of this and so I believe the voltage doubler will support about 250mA @250V. The most I have seen my valves draw is 36mA.
There are many examples of this design on Grant’s web page and some do have an extra meter to monitor the Anode voltage. I saw no fluctuation when I had a meter connected throughout the prototype stage, but I have to say I am working blind as I omitted one in the final build. I do not plan to add any stabilisation. However, voltages are patched through to the valve using banana leads so I could modify the leads and be able to connect a voltmeter through those and manually assess how stable the voltage is.
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 ?
Thank you for the feedback. I love hearing about the experience of others. Good idea on the variac and valves.
Is there any reason why you couldn't get rid of all that voltage doubler circuitry and use a 1:1 isolation transformer and a couple of small variacs to set the screen and anode voltages? That would give much more flexibility.
You could do that. It is a valid approach. The point about this design is that it is cheap. Costs of an insolation transformer and variacs could be higher. You will also need to rectify the output and make a negative voltage for the grid. The voltage double circularly is not too great anyway. That said I am think about a variac based plug-in module for the screen voltage. At least my final build has the ability to plug in power modules for screen and heater.
I am getting the parts together to build this same tester. Do you have a link to the meters you used
We need to be cautious about placing links in TH-cam comments. Just search for LED panel meters and you will see many options. I'm glad you are taking on the project.
Would you mind sharing which two transformers and which DC supplies you used? Thank you.
Any 12-0-12 50VA transformer will do. You can go to 15-0-15 if you want a 300V+ plate voltage. The heater transformer is a 6-0-6 30VA component. I connected the secondaries in parallel to provide more current capacity. For the meter supplies, I used generic 5V 5A output, AC110/220V to DC5V 25W Universal Regulated Switching Power supplies. These can be easily found on Amazon or eBay etc.
@@VintageandReclaimedElect thank you.
Fantastic. How about a design for DHT valves?
This will work with DHT valves. One side of the heater connection is grounded, effectively connected to the Cathode. The filament voltage can be applied to the other heater connection.
Nice job 🙂
Witch program do you use to draw stripboard and panel design
Thank you for that. I use Affinity Designer, but any drawing package will do.