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Poor Man's Valve Tester

 
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Poor Man's Valve Tester

Post by Sparks » Fri Nov 06, 2015 5:17 pm

Receiver Unit (Large).JPG
Receiver Unit
Valve Holder Unit (Large).JPG
Valve Holder Unit
Testing an EF80 (Large).JPG
Testing an EF80
Poor Man’s Valve Tester
This is an improvement of a simple valve tester that I built a while back. Essentially, the top unit is a one-valve reaction receiver using an EF91 run as a triode (anode and screen grid strapped together.)
An anode/screen current test facility is fitted. This is just two sockets for the meter with a shorting switch across them, inserted in the anode circuit. When current measurement is not required, the switch is closed. When the meter is plugged in, the switch is open.
Power to the unit is fed in on the right hand side via a four-pin Din socket and plug. The heater leads have crocodile clips fitted. For 6 Volt valves, I use a 6 Volt battery. For higher heater voltages, I use a variable transformer feeding into an isolating transformer, and then on to the tester.
The coloured jump leads on the bottom are left to right cathode (black), heaters (yellow), grid (green) and anode (red). The brass sockets above them are blanks, and just used to stow the jump leads when the unit is just being run as a one-valve receiver.
The lower unit is simply eight common valve holders, the two top left being Maza Octal and International Octal respectively.
The red sockets along the top are valve holder pin numbers 1 to 9 from left to right. The black screw terminals along the bottom are also pins 1 to 9 from left to right.
To test a valve, first tune a station in with the EF91 in position. This is just to ensure the receiver is working. Remove the EF91 and place the valve to be tested in the appropriate valve holder. Plug the five jump leads into the appropriate pin sockets along the top. The lower terminals are used for any necessary links. For example linking the cathode to G3, the anode to G2 in the case of a pentode.
Before I built this, I thought that the tangle of wiring under the lower unit might cause instability, but using only 45 Volts HT, it is all quite stable. I also made a crocodile clip with a socket on it for use on top caps.
I find that this tester works beautifully, and even heavy mains valves with high heater voltages work OK in it.
If you have a new valve as well as the ones to be tested, it is best to note the combined anode/screen current to compare it with used valves.
It is not idiot proof, because the user has to ensure the jump leads are plugged in the correct sockets, and also the correct heater voltage is used for the valve under test. Also, do not forget to take out the EF91 before testing a valve in the lower unit.
I used an EF91 because they are very common and dirt cheap! This little project occupied me for the best part of a week, and I am very happy with the results!
Bob

 
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Re: Poor Man's Valve Tester

Post by PYE625 » Sun Nov 08, 2015 10:06 am

Brilliant work !!
An alternative to the rather expensive testers on ebay I have seen from time to time :bba

 
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Re: Poor Man's Valve Tester

Post by Sparks » Sun Nov 08, 2015 10:45 am

Thanks,
I tested quite a few valves yesterday, including ancient B7 mains types with 4V 1.5A heaters, and they all worked. None of them minded the 45 Volt HT, and the volume on some of them was quite surprising. I am very happy with it, having given up hopes of finding a reasonably priced valve tester on Ebay. The most tedious part was wiring up the valve holder, sockets and terminals. I didn't draw a circuit out, but linked the sockets and terminal straight across, and then started joining them up to the pins one at a time - awful tangle in the end! :ccf
But there has been no sign of instability. The receiver is a bog-standard grid leak/reaction set-up with variable capacitor reaction.
The worst part was wondering if it would do the job after the marathon wiring job!
I was fortunate to find a variable transformer on a car boot sale for £5, and that supplies any filament voltage by feeding it into a normal mains transformer to isolate it from the mains. That was what decided me to build the tester, as prior to that, I did not know of any easy way to get funny heater voltages!
Bob

 
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Re: Poor Man's Valve Tester

Post by crackle » Mon Nov 09, 2015 9:30 am

Well done, it looks very nicely laid out.

Mike

 
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Re: Poor Man's Valve Tester

Post by Sparks » Mon Nov 09, 2015 10:50 am

Receiver Unit Wiring (Large).JPG
Receiver Unit Wiring
Thanks, yesterday, I tested some PL36 valves in it, and they worked OK. Here are two photographs of the inside. The air-spaced variable capacitor is the reaction. Initially, I used two small solid dielectric types, but found to my dismay that their capacity decreased as they were turned clockwise. The reaction then operating backwards felt a bit too odd, so I put the smallest air-spaced one that I had in to make it work the correct way. Tuning and reaction coils are my usual method of three 47uH RF chokes. Apart from that. it is all pretty basic. I doubt if many people will build one of these because of the boring nature of the valve holder wiring, but it certainly suits my purpose.
Bob
Attachments
Valve Holder Panel Wiring (Large).JPG
Valve Holder Unit Wiring

 
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Re: Poor Man's Valve Tester

Post by Greenstar » Wed Nov 25, 2015 5:50 pm

It's an interesting idea. I experimented a little in a similar line after reading The Impoverished Radio Experimenter books, which I don't rate totally, but have some good things in them. I'm thinking of experimenting with 20's circuits, looking for substitutes for early valves, and yes, found many valves work fine in a simple grid leak circuit, connected as triodes. Interesting to see this is true also with reaction. The EF80 is one I liked, works with 6v LT, DC, and low HT, and no shortage of 'em. It's a good crude way to see how valves behave, build a circuit similar to the one you want and and try a few. Valves one might not think are ok will work fine - possibly lowering working voltages offsets higher gain etc.
Tony

 
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Re: Poor Man's Valve Tester

Post by Sparks » Wed Nov 25, 2015 6:34 pm

Every type I have tried so far has worked. I can assess the emission by comparing the anode/screen current of the same types of valves with known good/new ones. I even tried one of those LOPT TV valves with the ceramic inside and top cap. Forgot the number at the moment, but it worked OK.
Bob

 
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Re: Poor Man's Valve Tester

Post by Greenstar » Thu Nov 26, 2015 12:52 pm

That's an impressive piece of wiring. Would 'do my head in'. You must have a logical mind. For my efforts I used a 12v battery, variable regulator and multimeter to get DC LT voltages, this supplied enough current for one valve.

 
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Re: Poor Man's Valve Tester

Post by Sparks » Thu Nov 26, 2015 1:04 pm

The wiring was easy enough, but I would have got very confused if I tried to draw a wiring diagram and follow that! I just linked the sockets and terminals directly across. Then I linked socket 1 to pin 1 on each valveholder, then I linked socket 2 to pin 2 on each valve holder and so on until it was complete! Not difficult or confusing, just tedious in the extreme! My variable transformer allows me to select any heater volts even up into the 40 Volts and beyond range!
Bob

 
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Re: Poor Man's Valve Tester

Post by Terrykc » Fri Nov 27, 2015 11:31 am

Sparks wrote:... The air-spaced variable capacitor is the reaction. Initially, I used two small solid dielectric types, but found to my dismay that their capacity decreased as they were turned clockwise. The reaction then operating backwards felt a bit too odd, so I put the smallest air-spaced one that I had in to make it work the correct way ...

Bob, there is an alternative way of doing this, although I've only ever encountered it once.

The circuit I chose - from several in a library book - for my first one valve TRF (in fact, my only one valve TRF!), used a fixed capacitor in series with a pot.

This was ideal for me as it saved me the cost of the solid dielectric variable capacitor and I already had the pot, rescued from a scrap chassis.

It worked a treat and the pot had a nice silky feel to it, which is more than be said of most of the solid dielectric caps available at the time (late 1950s).

 
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Re: Poor Man's Valve Tester

Post by Sparks » Fri Nov 27, 2015 11:47 am

I have made a number of reaction sets with various forms of pot control. But the problem I find is that after a while, they don't work very well, if at all. I believe that this is due to the relatively poor quality of the carbon track. Ideally, a wire wound pot should be used, but they are more expensive, and harder to source.
Bob

 
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Re: Poor Man's Valve Tester

Post by Terrykc » Sat Nov 28, 2015 1:17 pm

Perhaps this depends on how the reaction function is implemented. I think I've seen circuits with a pot used to supply the screen grid and other similar approaches but the problem here is that carbon pots don't like DC on the wiper/track.

It was very noticeable when transistor radios first became popular how quickly the volume controls started to become noisy (due to the leakage current in the electrolytic coupling capacitors) compared with their valved predecessors.

The circuit I built was conventional but used a pot in series with a fixed capacitor instead of a variable one: hence there was no DC component on the track.

 
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Re: Poor Man's Valve Tester

Post by Sparks » Sat Nov 28, 2015 1:34 pm

Even with this circuit (attached), I still found the pot failed after a while, and there is no DC on it. It was a very cheap one though, so maybe that had something to do with it. L3 lies physically alongside L2. L1, L2 and L3 are all 47uH RF chokes. L4 is half of an LT44 transformer!
Bob
Attachments
Two Valve Circuit with lettering (Medium).jpg
Two valve TRF

 
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Re: Poor Man's Valve Tester

Post by Terrykc » Sat Nov 28, 2015 5:27 pm

Mine was similar but was a one valve set. The headphone was a Government Surplus low impedance type and the output transformer was recovered from an old valve radio.

1V-TRF.jpg

 
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Re: Poor Man's Valve Tester

Post by Sparks » Sat Nov 28, 2015 6:15 pm

It looks like an adaptation of my circuit above, as the symbols seem to be identical as well as similarly placed, apart from the reaction, but I don't recall trying that arrangement myself, but if it worked, that is the main thing.
I also made a very smooth reaction control by physically rotating L3 alongside the fixed L2. I made it using an old potentiometer spindle with a button on the end holding L3. One side of L3 went to the brass spindle and the other to a slipring and springy brass bush. It worked really well!
Bob

 
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Re: Poor Man's Valve Tester

Post by Sparks » Sat Nov 28, 2015 6:33 pm

Here is my rotating coil reaction unit. One of the chokes is inside the old 25mm glass fuse.
Bob
Attachments
Reaction Unit 50%.jpg

 
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Re: Poor Man's Valve Tester

Post by Terrykc » Sat Nov 28, 2015 6:40 pm

Sparks wrote:It looks like an adaptation of my circuit above, as the symbols seem to be identical as well as similarly placed, apart from the reaction, but I don't recall trying that arrangement myself ...
Err - do you think that might be because I opened your drawing in Paint and edited it to suit my (memory) of the receiver I built about 57 years ago, Bob?  :)

 
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Re: Poor Man's Valve Tester

Post by Sparks » Sat Nov 28, 2015 8:06 pm

I thought it looked like my original drawing altered, but couldn't imagine how you did it, especially with Paint! I have a folder full of jpeg symbols and insert them one by one into a new Microsoft Word document using the grid to line them up by sliding them about. Then I print it out and put all the wiring in by hand, scan it back into the computer and add the lettering. All very tedious! :ccf
There are various similar reaction arrangements that I have used. Another has the pot across the reaction coil. The mechanical device shown above gives the smoothest results, but even so, the slip ring has to be kept clean, but it can be replaced by a flexible wire, but I just like "messing about" with these things, so it depends what I feel like at the time!
Bob

 
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Re: Poor Man's Valve Tester

Post by Terrykc » Sun Nov 29, 2015 12:14 pm

Sparks wrote:I thought it looked like my original drawing altered, but couldn't imagine how you did it, especially with Paint! I have a folder full of jpeg symbols and insert them one by one into a new Microsoft Word document using the grid to line them up by sliding them about. Then I print it out and put all the wiring in by hand, scan it back into the computer and add the lettering. All very tedious! :ccf
It sounds like it, Bob!

I don't usually bother with the grid as Paint doesn't have a 'snap to grid' facility. I copy and paste my symbols into Paint - one of each type I want - and arrange them along the top. It is much easier to copy and paste within Paint for duplicate symbols. I can also use Paint to flip and rotate symbols if I need to but I usually update my symbol library with the new variants for future use.

With Paint, I can move each symbol into position and draw the connecting lines as I go. The lettering is added using the Text facility and the top selection of symbols is easily cropped when I've finished.

You should try it - it really is much easier!

I love your symbol library - much better than the various ones I've found from time to time. Where did you get it from?

 
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Re: Poor Man's Valve Tester

Post by Sparks » Sun Nov 29, 2015 12:41 pm

Some I made myself and others I got from old circuits. I found a drawing section in Microsoft Word 2000 that is perfect for drawing symbols because the shapes can be snapped inside the grid and the lines made thicker if required. It also has standard shapes such as boxes with rounded corners, squares, circles, arrows etc, and a facility for filling in the shapes with either solid colours or patterns. I obtained the drawing section by clicking on View - Toolbars - Drawing, at the top of the MS Word document. The icons then appear along the bottom left of the monitor. It takes a bit of messing about to get used to it, but it is great. Sadly, it doesn't appear to be in Open Office or Microsoft Office, but I still have Word 2000 in my two laptops.
I will have a try using Paint.
Bob

 
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Re: Poor Man's Valve Tester

Post by Terrykc » Mon Nov 30, 2015 12:03 pm

Some folk are rather surprised at just what can be achieved with Paint.

All of my original schematics are produced using Paint as are derivations from other material.

I use it for producing and editing maps and all the artwork for these gifs was prepared using Paint:

Image Image Image

 
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Re: Poor Man's Valve Tester

Post by Sparks » Mon Nov 30, 2015 1:10 pm

They are very professional looking maps! :) I have only recently started experimenting with paint, beginning with the useful resizing facility.
Bob

 
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Re: Poor Man's Valve Tester

Post by Terrykc » Tue Dec 01, 2015 10:13 pm

Sparks wrote:They are very professional looking maps! :)
I think the Ordnance Survey must take the credit for that - I only modified them to suit the purpose!

Because these maps are going to be published on the internet, copyright is of prime importance and I either use this OS map because it is covered by the OS OpenData licence or Open StreetMap which, as its name implies, is open source.

The problem is always getting the required map to fit on one A4 sheet at a scale which is clear enough for the required level of detail - it certainly is a headache sometimes!


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