Poor Man's Valve Tester

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

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!
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

Well done, it looks very nicely laid out.

Mike

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

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

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

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.

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

... 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).

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

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.

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

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.

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

Here is my rotating coil reaction unit. One of the chokes is inside the old 25mm glass fuse.
Bob

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? 

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!
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

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!

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?

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