Split from https://golbornevintageradio.co.uk/forum...p?tid=9110
In principle you can test a valve with a number of variable power supplies and a number of meters. How many you need depends on the type of valve. You also need a means to connect all these to the correct pins of the valve and try not damage you or anything else while you're doing it. There are also important refinements like making sure the valve doesn't decide to oscillate at some un (insert $deity of choice) ly frequency.
The rest is detail and convenience. From the simplest vintage valve testers to a Tektronix 570 curve tracer they are all making these measurements. With greater or lesser accuracy. With greater or lesser convenience. With greater or lesser detail. Slightly off to one side is the uTracer:
https://www.dos4ever.com/uTracer3/uTracer3_pag0.html which uses the cunning trick of pulsing the voltages on the valve's electrodes. This comes with its own set of advantages and disadvantages.
Then there are all the things a valve tester won't tell you such as high frequency characteristics and pulsed power performance.
A big and interesting subject.
Many thanks Jeffrey - looks a very interesting project.
I was thinking of the "simple" tester to start with just to get going again and then I want to go back to the "Sussex" that I have built the circuit and have virtually all the parts to build from the model back in 2010/11 (may need some mods).
Its fascinating really as in 2010 I had my spinal operation (laminectomy/dissection) and on Friday 3rd May this year I had my spinal denervation (microwave to "kill" my trapped compressed nerve) at Southend Hospital (they were superb in treatment) and in both occasions I'm keen on working on valve tester projects.
I'm still recovering but keen to pick this up albeit I may take a while to get going.
Best Regards
Rob
As I understand it, the Sussex is a simple tester. It applies voltages and measures currents. One thing that makes even simple testers look complicated is the all the switching or patching needed to connect the right pins of the valve to the right voltages and meters. Plus all the different valveholders needed to test a wide variety of valves.
I have a lash up bit of scrap chassis, tag strip, b9a base, couple of switches and 10 turn pot for grid voltage, plus suitably connected 4mm sockets for test leads to connect. I have a couple of lcd multimeters bought 50p each at a rally, minus leads and battery but both working, plus my usual bench lcd meter.
I have a Solartron 500V 100mA variable psu that also gives 6.3V, plus my small Farnell 30V 1A bench psu for grid voltage.
For some protection of ht current, I have an les 4V 60mA or so bulb in a holder fixed to the ht + terminal in series with supply when testing low current valves. I have a stock of maybe 100 bulbs! Usually blow with a brilliant flash when I accidentally short something within my lash up!
This jig is for ecc and with my adapter lead also 6sn7 or l7 etc. I put some ferrite beads on the leads close to the base.
For audio output valves, I have another similar lash up with my base wired for el84, again adapter leads for 6v6, 6bw6 etc.
Comparison checks show the cheap meters as within 2% accuracy and good enough to measure valves with.
Just need to be careful where I put my fingers sometimes with ht around from my meaty psu!
My ht psu would be better if stabilised for small changes in load, as being to the rear of my bench I reach across to vary the voltage, it could also do with a fine pot as well, the wirewound within seems a bit jumpy around 250v setting.
I suppose I ought to modify the psu with a stabiliser circuit and fine / coarse controls, but that is still on the to do list, has been for 10 years or so!
Rob
I don't often have the need to test valves but a couple of years ago I needed to characterise some rare triodes which had come my way and which I wished to sell for BECG funds. They were on B4 bases. The filaments were something very odd like 10V 1A. I used a bench HT supply for the anode and bench LT supplies for filament and grid. I rounded up some DMMs and lashed up a horror story with lots of croc clip leads and 4mm plugs.
The data sheet for these valves had a comprehensive set of figures so I did a series of spot checks. I could have plotted the curves if I'd had the wish and patience to do so.
The BECG benefitted by several hundred pounds. I survived without any belts
I like Rob's refinement of a lamp limiter. I suspect Rob's HT supply was, like mine, a Solartron SRS153 which is very handy but not really regulated. I have a SRS151 which is fully stabilised but so big and heavy that it only comes out when really needed. I recently bought a Farnell E350 which will probably become my usual bench HT PSU.
My psu has a pair of 5b254m.
I had a box of 350 to 450v electrolytics to test and reform.
I used some tag board and as I had a load of 9k1 resistors, used one in series to each + lead of the 6 I had. The 6 negative leads paralled up, both leads terminating with miniature insulated hook spring clips.
6 capacitors standing like soldiers, tags at the top and all my insulated clips attached.
Started psu at around 200v, gradually increasing. I monitored the voltage drop across each resistor in turn to check I wasn't charging too high a current.
The times when I reached across to adjust the voltage knob behind this set up on my bench (situated about 5 inches above my bench) and my bare arm brushed against a pair of terminals!
I am VERY sensitive to shocks. At work, I used to repair a lot of ground radio ATC equipment using the 28V dc input to give better monitoring of curent, especially some tx drawing 16A. Then final test on mains.
Sometimes, when fault finding, if my bare arm or elbow (we wore tee shirts) brushed lightly against the chassis -ve and the same or other hand touched the supply rail, I would rapidly react. Yes, 28V.
Now, imagine around the same year having nerve conductivity tests for hand and arm nerve testing. One electrode clipped on my finger and other elsewhere whilst pulses were fired at me.
I was going OOH OUCH etc. Very loudly.
The doctor had to abandon the tests because I was getting so stressed. "It's only a few milliamps" she said. What voltage I asked, but never was told.
She then explained there may be another way to investigate, but not very pleasant but described the method, to which I agreed to give it a go.
This involved 2 electrode wires attached to the likes of tiny needles. One was stuck just under the skin on my foot, the other into my tongue. This didnt really bother me.
What was more intereesting wac the oscilloscopetype display showing what looked like a load of audio crackling and sounding like it on the loudapeaker. I neede a gulp of servisol!
My wife had been in the waiting room outside, together with other patients waiting their turn.
She said they all looked at each other very worried indeed at the time when they heard me shouting!
Rob
(06-05-2024, 01:05 PM)CambridgeWorks Wrote: [ -> ]My psu has a pair of 5b254m.
Here's the SRS153 schematic. The CV428 is equivalent to the 5B/254M:
http://www.r-type.org/exhib/aab0149.htm As you can see, there's no attempt at stabilisation except that the cathode followers may have a lower output impedance than the raw supply. Note all the stopper resistors to stop the valves, which are designed for RF service, hooting like mad.
These are very good, solid PSUs. Not an electrolytic in sight. All high quality paper capacitors.
Hi Rob, a further extension of valve testers for the audio enthusiasts would be to ad a variable audio source and run the output through a computer sound card.
This will give a good indication of distortion levels at various drive levels. It can also be used to check intermodulation distortion.
This is an extension of the scheme using fixed frequency injection on the AVO VCM's
Ed