Heater-Cathode leakage test

[Martin Manning]

I'm playing with ideas for adding a simple h-k leakage test to my uTracer. I have seen a few h-k insulation breakdown failures, most often when a tube is used in a cathode follower circuit that results in cathode voltages up to 200V. What is the experience in the group? Do you see this as a common failure mode?

[Martin Manning]

I'm going to go ahead with this. It's very simple and very small, 24 x 28mm (and I don't have much more than that to spare!).

This circuit was initially designed to test for H-K leakage. It switches a bi-color LED from Green to Red when it sees resistance going from ~3M to 1.5M. A BJT changes the LED color when a small leakage current (20-30 uA) flows through a voltage divider connected to the transistor's base. The indicator circuit is powered from the raw negative voltage supply (-40V), and the cathode terminal (+20V), both of which are present when power is on. This provides nearly 60V potential for the H to K leakage test. A 3PDT switch (which supports the PCB) disconnects the heater power source, and connects DUT H and K to the indicator circuit. This test is run after the DUT has been connected to the uTracer panel terminals for tracing/testing, and it can be engaged with the heater and cathode at temperature. 

Alternatively, The DUT can be checked for H-K leakage plus shorts and heater continuity before it is connected to the uTracer. The DUT is inserted, uTracer power is turned on, and the indicator circuit is switched in. The pins of the DUT are then probed using the H and K terminals. For example, the cathode terminal is connected to the DUT pin 1 jack, and then a patch cord connected to either heater terminal is touched to pins 2-9. The cathode terminal connection is then moved to pin 2, and the heater cord is touched to pins 3-9, etc., until all possible pin-pin connections have been checked.

[Davo]

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Op 8 jul. 2022 om 03:17 heeft Martin Manning <mman...@fuse.net> het volgende geschreven:

I'm going to go ahead with this. It's very simple and very small, 24 x 28mm (and I don't have much more than that to spare!).

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[Davo]

Hi Martin, how you think about this design?

I made i this design somewhere in feb ‘22

It’s made with a 3x4 Rotary switch to check to check multiple shorts & leakages and to protect the tester

Leakage tester supply..

The Voltage dependence Resistors could be left out in this design..

Kind Regards,

Dave Achterberg 

Op 8 jul. 2022 om 03:17 heeft Martin Manning <mman...@fuse.net> het volgende geschreven:

I'm going to go ahead with this. It's very simple and very small, 24 x 28mm (and I don't have much more than that to spare!).

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[Martin Manning]

Hi Dave, I saw your design when you posted it earlier this year. I don't have room for anything as elaborate as that in my enclosure, so I was going for a very minimalist design. I'll post a photo when it is installed and working.

[Davo]

Ah see, if space is a problem you try to keep it as small as possible.

Did you took in consideration that with a H-k short can short out the power supply.

Or did solve it with a resistor or little bulb?

If possible i should try to add extra switch/switches or rotation switch to test other elements of the tube also..

The most space of my design went to the 48v acdc converter which was quite slim format.

Maybe one board for all the utracer addons could be a good idea to keep it as small as possible?

Just some thought about, it’s always good to talk about innovations to take ideas to a higher level.

Op 8 jul. 2022 om 05:07 heeft Martin Manning <mman...@fuse.net> het volgende geschreven:

Hi Dave, I saw your design when you posted it earlier this year. I don't have room for anything as elaborate as that in my enclosure, so I was going for a very minimalist design. I'll post a photo when it is installed and working.

To view this discussion on the web visit https://groups.google.com/d/msgid/utracer/4e6ea08c-47d1-4c8d-85ee-79edb2841584n%40googlegroups.com.

[Martin Manning]

A H-K short is dangerous if you are using the internal heater supply. I almost never do that, but if it is used an H-K short check is a good idea. I also wanted a test for H-K leakage (a source of hum and other noise), and the transistor circuit will respond if there is even a small amount of leakage current. There is no need for an additional power supply since the uTracer already has a negative power supply that can sink the ~4 mA that the circuit uses, and if a patch cord arrangement is used to connect the DUT, the option to test all other pins for shorts is an added bonus that is available without the need for a rotary switch.

[Martin Manning]

This shorts and leakage test function is now installed and working as expected. I have it in my uT3, but the circuit could be made to work with uT6 too.The uT6's  negative voltage is -85V, which would result in over 100V from H to K. In that case it might be better to use the -15V supply instead, and change two resistor values to adjust the LED current and the sensitivity.. I have extra boards in case anyone is interested. 

[Davo]

I thought i replied your answer lol

But somehow something went wrong haha

I’m not a fan of patch cords when working with high voltages.

Personally i prefer a switch matrix for safety reasons & keeping things 

Organized.

It’s good  to see you have the option to test multiple elements.

There  many roads that leads to rome!, as long as you get there it’s all okay haha

The board is looking good Martin!

Clever design with that switch for attaching it to the panel

I was wondering do you prototype your own boards also?

Because i always see your boards made by those Chinese PCB Houses

Keep up the good work!

Kind Regards,

Dave Achterberg 

Op 12 jul. 2022 om 23:13 heeft Martin Manning <mman...@fuse.net> het volgende geschreven:

This shorts and leakage test function is now installed and working as expected. I have it in my uT3, but the circuit could be made to work with uT6 too.The uT6's  negative voltage is -85V, which would result in over 100V from H to K. In that case it might be better to use the -15V supply instead, and change two resistor values to adjust the LED current and the sensitivity.. I have extra boards in case anyone is interested. 

To view this discussion on the web visit https://groups.google.com/d/msgid/utracer/30576650-6353-43fb-848f-98b6efd6c396n%40googlegroups.com.

[Martin Manning]

Thanks, Dave. I have designed and etched many PCB's myself over the years, but I don't like dealing with the chemicals, and the boards do not have plated-through holes and a solder mask like commercially made ones. 

IMO the flexibility of the patch cord system wins. I have traced tubes that won't fit in my socket array, and many other types of components with it. High voltage is not a problem since there is none present when the connections are being arranged, or when probing the DUT pins using this shorts and leakage tester. Switches would be faster, and that might be important to someone who is in the business of repairing tube equipment. In the extreme, I've seen a setup that automatically makes connections using a micro controller and relays. It's personal preference as you say.

Here are a few pictures of my uTracer. As you can see, very little room was available for a shorts and leakage test circuit. I've managed without having such a feature for almost nine years without incident, but it was an interesting project and it seems like it will be useful. On the left in the inside photo you can see the Low Vg loupe PCB.

[Davo]

I Made a few months ago the Tor Tester addon also, it’s still on a piece of card board

But i still have to make my final deckplate.

I haven’t got much time to completed all the things i wanted to add haha

So many projects i’m working on…

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Op 13 jul. 2022 om 13:19 heeft Martin Manning <mman...@fuse.net> het volgende geschreven:

Thanks, Dave. I have designed and etched many PCB's myself over the years, but I don't like dealing with the chemicals, and the boards do not have plated-through holes and a solder mask like commercially made ones. 

To view this discussion on the web visit https://groups.google.com/d/msgid/utracer/2e34e419-e65f-4086-b882-052dd73a535en%40googlegroups.com.

[Davo]

Ah ok, yeah i can understand it about the chemicals though.

Iron Chloride can be nasty stuff if you spoil it!

I always find it a challenge to make a single sided board haha

Sometimes it can be a real pain to make a good single sided design.

With simple designs i have no problem sending it to a pcb house, but in general i prefer prototyping before send it to a pcb house.

Designing pcb’s is way more easy as back in the days.

Way back it was a real art to make a pcb! Nowadays with Kicad it’s so easy lol

But if ure that serious with repairs why don’t you get a Röhrentest?

It’s quite a serious and expensive build, but in my opinion the best thing at the market!

Btw you have a quite slim design!

I still have to finish my build haha

But it’s going to be a tester in a case with screen etc.

My goal is to have everything in 1 case.

Utracer+addons, computer, standard tube tester with scope etc.

Anyways keep up the good work Martin!

 

Grtz, Dave

Op 13 jul. 2022 om 13:19 heeft Martin Manning <mman...@fuse.net> het volgende geschreven:

Thanks, Dave. I have designed and etched many PCB's myself over the years, but I don't like dealing with the chemicals, and the boards do not have plated-through holes and a solder mask like commercially made ones. 

[Johan Bekaert]

Hi all. I built this little circuit with the option to use patchcords to check all the pins of a tube. But I don't use 60V; I use the 19V that powers the uTracer. To make it work I changed the resistors to resp 86k, 56k and 3k3. It works. However when I test it over a resistor, the red led will come on up to around 250k; anything more it stays off and the green stays stubbornly on. Nowhere near the 1M5 you mention... of course, it will warn me well enough in case of a short; nevertheless I would like to see it work like yours. Or does it absolutely need the 60V? Thanks for your help! 

Grtz, Jo

Op donderdag 21 juli 2022 om 22:50:38 UTC+2 schreef djda...@gmail.com:

[Martin Manning]

Try 100k for R1, 1M for R2, and 4k7 for R3. The transition should then be from 1M to 5M.