Tube aka Valve Tester design

[markfff]

I've started a tube tester project of my own and scouring the web for ideas led me across the pond to this thread https://www.vintage-radio.net/forum/...ad.php?t=69201 about Jan van Eyck's tester. Unfortunately it's an old thread and links to more information lead nowhere. Does anyone have more details about this tester that you'd be willing to share?

While here I discovered the Sussex Valve Tester. It looks like a great design and I downloaded the manual for further study, so thanks for that.

Though I've already built a patch panel with a dozen tube sockets, I'm currently still in the design stage for the rest of it. My ideas are to use a 120/240V isolation transformer (since they're relatively easy to find) for the plate & screen voltage, feeding a multiplier and variable high voltage FET regulators.

I'd like to accomodate the full range of filament voltages so I thought about a 25.6VCT transformer and a variac, bypassing the transformer for higher voltages (I don't want to try to find a transformer with some 20-odd taps). Maybe a variable switching regulator might be a better choice, but I don't know about feeding DC to the filaments, especially for directly heated cathodes.

To control this beast I thought to use a Raspberry Pi computer, and have the tube data stored in plain text files on a USB drive so they can be modified and new tubes added at will.

If anyone has thoughts or suggestions about this project I would greatly appreciate hearing them. Thanks

[Craig Sawyers]

We have our very own design called the Sussex. Do a search and you'll soon find lots of information.

Alternatively here it is https://www.vintage-radio.net/forum/...ad.php?t=48853

Craig

[Cobaltblue]

Originally Posted by markfff

While here I discovered the Sussex Valve Tester. It looks like a great design and I downloaded the manual for further study, so thanks for that.

Originally Posted by Craig Sawyers

We have our very own design called the Sussex. Do a search and you'll soon find lots of information.

Alternatively here it is https://www.vintage-radio.net/forum/...ad.php?t=48853

Craig

Looks as if he already knows about the Sussex

Cheers

Mike T

[Electronpusher0]

I also vote for the sussex.
If you build it according to the manual it works well and there is plenty of scope to adapt it if you wish, I did this including multiple transformers instead of a single one.

If starting from scratch I would recommend contacting Ed Dinning on this forum, he would be able to wind you one with a 120V primary and all the secondaries you need for the sussex.

Peter

[Craig Sawyers]

Originally Posted by Cobaltblue

[
Looks as if he already knows about the Sussex

Cheers

Mike T

Somehow I missed that sentence!

But in the same vein - https://www.dos4ever.com/uTracer3/uTracer3_pag0.html
http://www.roehrentest.de/EnglishInfo.html

Craig

[Robert Gribnau]

A link to the article by Jan van Eijck and John Hupse (translated in post #10 of the thread you linked to): http://nvhrbiblio.nl/biblio/tijdschr...RHT2011033.pdf

Attached a picture of the tester.

[trobbins]

Another option is to acquire a simple vintage tester and upgrade/extend it. Simple emission type testers typically came with all the heater voltages. Perhaps then use your breakout sockets to access grid, screen and anode for particular valves, and include your additional circuitry and metering in an external box.

[Electronpusher0]

Originally Posted by trobbins

Another option is to acquire a simple vintage tester and upgrade/extend it. Simple emission type testers typically came with all the heater voltages. Perhaps then use your breakout sockets to access grid, screen and anode for particular valves, and include your additional circuitry and metering in an external box.

For example:
https://www.vintage-radio.net/forum/...ighlight=MHSVT

Adding gm measurement to the Mullard High Speed Tester

Peter

[retailer]

If contemplating modifying an emission type tester be aware that many of them have marginal transformers powering the filaments, they may be ok testing say a 6AU6 but try an EL34 (1.5A for the heater) and the heater voltage will sag.

[David Simpson]

As retailer says, a sturdy regulated source of heater/filament voltage is essential. For my DC Tester I use an external 2Channel 30V/2A stabilised LV DC Modern PSU with a parallel/series function, & an accurate LCD display of voltage & current.
For engaging the final "Test" function, i.e. the valve under test drawing Ia in accordance with the chosen Vg, up to100mA plus, I operate a sturdy DP/ST Spring Loaded toggle Switch. Which, in conjunction with an even sturdier DP Relay, only connects Cathode, Anode & Screen for as long as it takes to read the relavent Ia & Is for writing down or recording in a tabulation(for drawing-up an Ia/Vg Graph). Just a few seconds of pressing down your pinky is all it takes. A serious safety factor which means that the valve under test isn't phooked if inadvertantly you've selected the wrong Vg, and also protects the HT transformer( an ex AVO VCM MK2 perhaps?) you've fitted in your tester.

Regards, David

[trobbins]

I can only speak for my 1948'ish emission tester, a Palec VCT-2, which was quite common in Australia. It has filament voltage steps to 117V. Given its release date it doesn't have the likes of an EL34 in its valve list, but it does list 5V 3A heater diodes like 5U4, 5X4, 5Z3, and an 809 which is 6.3V 2.5A.

A sample 5U4 causes the tester heater voltage to sag -10% at the octal pins, so not too bad given the internal wiring and three series switch contacts in the circuit, and the terminal voltage can be tweaked up to 5.0V using the line adjustment.

[markfff]

Thanks for all the info, I definitely received an education and some great ideas. If I just wanted a tube tester I could buy a vintage unit, though I would be more inclined to build one, like the Sussex, since it's seems well designed and thoroughly documented. But I also wanted the challenge of trying to build a better mousetrap. My primary goal is to have it fully programmable without using an external computer, hence building it around a Raspberry Pi. Tube or valve data and testing parameters for each type would be kept in a separate text file that can be modified or extended at will. It may take a while, but I'd be happy to share my progress here.

As for filaments are there any obscure problems to worry about if using DC, especially for directly heated cathodes? I take it I'll need to supply at least 3 or 4 amps at the low end of heater voltages.

[Dekatron]

There are a few dicuments writren on the Roetest and how it measures directly heated tubes and what to think about, check these (or Google ” roetest directly heated”): http://www.roehrentest.de/Gleich-Wec...heizung_EN.pdf and http://www.roehrentest.de/THeizung_EN.pdf

If you ever are in doubt about your DIY-tester compare DC-heater with AC-heater to see if it works correctly.

/Martin

[David Simpson]

Hello again Mark,
As you've raised concerns about using DC for Heater/Filament supplies, best bet is to look back to the early days of Valve/Tube usage. The term "Filament" is the early name for "directly heated cathode". This method was used since the days of WW1(bright emitters, dull emitters, etc.) through to the late 1920's when improved methods of coating with thoriated tungsten brought about the use of indirectly heated cathodes. Also, back in those early days, all radio voltage supplies were DC - from Batteries, and in some cases - HT-wise from premises supplied with DC mains.
Just about all the analogue Valve Testers/Valve Characteristic Meters(VCM's)(now vintage items in their own right) you'll read about on this Forum & others are "AC operating" for their testing proceedures and their Heater supplies. As Grid voltages are supplied from seperate circuitry - the Cathodes are connected directly to HT & LV negative. This is achieved in the likes of AVO testers by the thumbwheel selection of "H+" & "H-". But then, AVO tells us, for example, on page 4 of the MK3's Manual(and in all the VCM & CT160 Manuals) to connect "Heaters" to a pure DC supply for the setting up of a "Standardising Rig" using Labarortory/Workshop equipment & AVO multimeters.
But hey - expand that recommended standardising proceedure and you've got the perfect DC Valve Tester. By all means plan a software driven tester, but first(don't run before you can walk), build a small DC supplied tester(just using IO, B7G & B9A valve holders) and have a jolly good play with it.

Regards, David

I suppose you could do a switch that reverses the DC, and then take the mean. One thing not to forget is that series heater valves specify a current, the voltage is a side effect.

[markfff]

So it seems the main thing to worry about is the voltage gradient across the filament. I think I will try a DC supply, as it should be a lot easier to vary the voltage (or current as the case may be) electronically. Apart from a recent radio restoration I haven't worked with tubes (except for x-ray tubes, electrically just high power diodes) in decades. Since I'm pretty much de facto retired at this point, I've been lining up projects and also have a Hallicrafters S-76 receiver, and a couple pieces of test equipment in the queue. I certainly have some catching up to do, so thank you very much for the info and insight.

[Skywave]

I would use D.C. for the heaters. Use a suitable L.V. winding (or windings) on the embedded mains transformer, rectify and filter it, feed that d.c. to a suitable solid-state regulator with a switch that changes the voltage at that regulator's 'common' connection so that you then have range of regulated d.c. voltages: e.g. 1.4, 6.3, 12. You could also incorporate an 'external d.c.' position with appropriate sockets on the tester's front panel to use an external d.c. source from an external PSU for other, rarely encountered voltages. And, if the internal d.c. supply has inadequate current capacity for a particular valve, use that external source.

Al.

[trobbins]

Note that making a DC supply for a valve heater that needs 1.5-3A, such as for a rectifier or an output stage sweep valve would typically subject a tester filament winding to a significantly higher current requirement (eg. 2x). So an internal DC supply is likely fine for say up to 1A heater valves, but a concern for higher current requirements beyond say a 6L6.

[G3PIJpeter]

There is an interesting design for a simple but effective mutual conductance meter from the 1950s at http://www.r-type.org/articles/art-118.htm and an updated version at http://www.r-type.org/articles/art-237.htm

I adapted the ’50s design for use with audio oscillator input and ‘scope output which, with switched balance pots, produces clear (and believable) readings of mutual conductance from 0.5 to 14. I wrote an article about this version that was published in Issue 55 of the VMARS ’Signal’ magazine.

Peter G3PIJ

[Ed_Dinning]

Hi Folks, the Sussex transformer is rated for 3A up to 6.3v and 1A at 12.6v

Ed