New boy.

[joebog1]

Morning all,

So I joined after following a thread from UKVRRR, about valve testers.

There was a reference posted here some 12 years  ago about a tester that I wished to access.
The refence came from ms660. Thats his name on VKVRRR.

I am at present designing my own valve tester that I am specifically looking at for audio testing.
YES I am an audiophool, NO I dont repaint valves or mark them Mullard.
I dont do guitar amps with anything other than ordinary valves. (I dont have any pixie dust ) so amps are very standard, but robust.
I am almost 70, and have spent my life in electronics, some of it exciting, much of it boring.

So to the real point of this thread. Apart from my introduction.
I am designing my own valve tester for small valves. Up to KT88 or 6550 level.
I have no interest in audiophoolery using single ended 3-1000Z triodes. 

The thread I tried to download is by  Joe and is a scan ?? from a design by W.T. Cocking, 
and is in this thread:

https://golbornevintageradio.co.uk/forum...p?tid=2758

So, as my introduction I have explained why I am looking.

I invite any questions, criticisms, or advice,  fellow members may have.

I will post as I have questions, and have navigated my way around a new website.

Thanks in advance

Joe

[Mark Hennessy]

Hi Joe - nice to see you here

Just in case you missed it, that document is in The Archive, which is a special area of the forum - the way that works is explained here: https://golbornevintageradio.co.uk/forum...elp&hid=11

All the best,

Mark

[Mike Watterson]

See also
https://www.dos4ever.com/uTracer3/uTracer3_pag0.html

I have one of his curve tracers. You can test valves without data if you can figure the pin connections and heater / filament voltage. I've also used a friend's big AVO, maybe the CT163 and replaced meters on several AVO testers. In one case I added an op-amp to replace an unobtainable meter with one needing a much higher current. I used the 2nd op-amp in the package for offset adjustment rather than use an expensive instrumentation type.

The best test is of course in the intended circuit. Historically the most important use outside a factory or lab was valve based TVs due to number of valves. A valve tester isn't really needed for restoring audio amps or radios as checking the actual circuit voltages tells you more.

I've only much used my tester for Russian rod tubes that are like pentodes. I've not found any need for EL84/EL41/EL95/ECL82/ULxx /KT66/ EL33 or EL34 output valves in radios or amps I was repairing. I used the TV shop's tester more in the 1960s as I didn't realise I could check the valves in the radio by measuring the voltages. I wasn't even a teenager when I got my Philips EE set, WWII era R1155 and Lady Margaret Battery valve sets.

[ppppenguin]

Welcome to Joe from the sunny south.

One thing that most valve testers can't do is sustained high power operation. Many will suffer burnouts, the Dos4ever design uses pulsed testing.

On the odd occasions I've wanted to test a valve I've used assorted bench power supplies and DMMs. Messy but effective. Slow if you want to plot characteristics but pretty much guaranteed accurate.

[Mike Watterson]

On the odd occasions I've wanted to test a valve I've used assorted bench power supplies and DMMs. Messy but effective. Slow if you want to plot characteristics but pretty much guaranteed accurate.

Best solution for very occasional testing or matching or unusual parts. I do have a DMM with serial out and I've seen programable PSUs, so the lash it together option can be partly automated.

Even the traditional testers often use a half wave unsmoothed supply for HT so that there is no need for a regulator, just adjust the mains input tap to the "cal" position for correct HT and LT. So they don't use the power levels implied by the knob settings. A 50 Hz half sine pulse testing.

The uTester can do continuous for low HT currents which allows magic eyes to be visibly tested. All testers need an additional external resistor to test magic eyes.

Also regular testers are useless to test conversion gain or other aspects of mixers. Problematic even for static tests for some kinds of beam-switching tubes, octodes, nonodes, triode-pentodes and triode hexodes without additional PSUs.

[ppppenguin]

Mike, that's all correct for more complex valves and at high frequencies. You also can't really test pulse power valves such as PL36 and other line output types properly with a valve tester.

But Joe's primary need is audio valve testing. A limited number of types, some fairly high power and possibly wanting to run them at full power for extended periods. That's a much simpler proposition than a universal tester. With few exceptions the heater/filament supply will be 4V, 5V or 6.3V. Then you need a good (and lethal) HT supply and a respectable screen grid supply. The grid bias is supplying little current, even if you're running the valves into grid current. I reckon I could test (for example) a KT88 with a bench lash up easily enough. It's a lot easier if you make up adaptor plates with the valve pins wired to 4mm sockets. Then everything can be connected with standard 4mm plugs.

Don't forget the ferrite beads. The circuit won't know it's only meant to do audio. Some audio valves will quite happily oscillate at radio frequencies.

[Mike Watterson]

Yes, a simplified tester specially for audio power valves is a reasonable idea. You also don't need as many socket options, though perhaps an adapter per base with 2mm or 4mm wander plugs to the test system?
Maybe even two valves with grids, cathode & screens parallel and only the anodes separate with two meters or a meter with two movements on one scale or two parallel bargraphs?

I'm not sure as it's not something I've ever been very interested in.

Indeed any audio valve can oscillate at RF, even if only a few 100 kHz. Same even with power FETS even that have 2nF or higher gate capacitance.

[joebog1]

Well, I have been in the game since I was about eight, when dad and I constructed my first radio. 
So I have been looking at a valve tester all my life
and I have discovered that its cheaper and easier to build one rather than buy one. Buying on the normal auction sites can be a disaster, 
although I dont think everybody would be out to make a killing. I have been collecting digital panel meters, but so far cannot find a useful one at the right price, 
AND that has a floating ground power supply so I can hook up six of them to a single supply for the digital readouts. All of them I have found so far are common earth
for the measurement zero and the power supply zero. That makes things go boom and let the magic smoke out. 
I have been designing and winding transformers all my life, and although its easy enough to wind an extra ?? six supplies, I still have to rectify them to get DC,
and ideally would use a little regulator to make readings as stable and repeatable as possible. 

I have assembled a set of iron, a set meaning HT, and screen on one transformer, Bias and heater on another so that I cannot switch on the HT without having a hot valve and at least some bias on the grid.
Valves go boom and let the magic smoke out too, if there is no bias.
So I have 500 volts DC available at about 1 amp, which will supply my HT and screen voltages using 807's or CV 428 ( same as 807 but in a loctal bottle ) as the series elements, initially two for HT and  one for screen, but upgradeable by adding another the same to each supply if they struggle at low HT voltages. Bias will be -100 volts and will be gas regulator stabilised and have a small amount of  positive ( so I can test in class B ) controllable through a ten turn pot. All of these supplies will have volt and milliamp meters so I can see and plot very easily what a particular valve is doing.
I will also be able to match valves for more critical applications. 

So my posting and explaining myself is post one of the fifteen required to access the the archive. I am patient and have discovered quite a few interesting posts here to read in any case so it wont take long.
I have collected every piece of information I can find on the net regarding valve testers in general ( problem being an ex engineer, you require documentation ) and W.T. Cocking did some work starting almost a century ago, that I dont have yet. I am hoping all the information mixed into a big pot of soup, will fetch me a real, decent valve tester when its dished up.

Thanks to all for you interest and comments. I will keep you all posted.

Joe

[ppppenguin]

If you need a floating power supply then small DC-DC converters are inexpensive. Simpler solution than lots of transformer windings etc.

Example to show general type:
https://uk.rs-online.com/web/p/isolated-...rs/2233683