The "Sussex" Homebrew Valve Tester.

[stoned6]

Hello Peter, Ed and Keith, all builders...

Thank you for your kind comments on my eye - I was rather optimistic in thinking that it would only be a few days after the operation and my sight would be back to normal. In fact it's going to take many more weeks before I can see normally again...

But, even if I cannot do any work on my valve tester, I can at least use the computer, for short periods only.

What is this "glossy magazine pages" and your artwork for PCB’s about?

I have bought 2 X 8Watt UV lamps, with ballast and starters etc, and I will try and make a UV exposure unit. I have some Ferric Chloride, developer and photo-resist boards, and laser printer film to print the PCB design onto - I don't really know what I am doing, but I will learn from my mistakes!

Ed has mentioned the difficulty in producing quality home made boards and the possibility of having them made by a proper PCB maker, if there is enough interest by other builders, or future builders, to lesson the cost.
Ed, I’m going to show my age here…I used the original EASY PC DOS ‘Number 1 Systems’ version when it first came out, and had a few problems with because it kept running out of memory, but they sent me the Extended Memory DOS version free of charge.
I have been using EASY PC ever since – I think we are on VER. 15 now.
In fact, using the DOS Extended Memory version all those years ago, I managed to complete my first 4 layer PCB, about 8” by 10” !!! It’s a bit easier now…
I prefer to use 2 or 3, or perhaps more, PCB’s rather than have everything on one PCB – I can then modify, or upgrade, fairly easily. I do not want my eggs all in one basket…

But I'll give it a try when my eye is better...
I have about 40 or 45 ferrites so I will use them on the Grid 1 wiring, although I don’t think I will have enough.

Peter, the ICL8038 oscillator, you only need +12V, not + and - 12V - you only need plus and minus 12V if you use my amplifier chip and RMS to DC convertor.
I can see your problem, because the your circuit uses minus – 48V(or is it -24V) for the relays, and for the grid bias, and minus 10V for the original Oscillator circuit…
Can you put a small extra winding on the transformer to give about 9V AC? It only needs thin wire as we only need a few milliamps at 12V DC.

I am interested in the valve amplifiers you build – what sort of power output, what valves do you use, and what is the design?
Do you use vintage components in the amplifiers? What about the output transformers? Is it SE or Push-Pull?

Sorry, many questions, but I have spent at least a year studying valves and their characteristics and valve amplifiers so that I can design my own set of Hi-Fi power amps (two mono-blocks with a separate pre-amp).
I attach a picture of my prototype/test amplifier, and a picture of what I should be working on, when my eye has mended.

‘Her indoors’ is not yet convinced about having two, or three, glowing electronic amplifier ‘things’ in the living room. But I am working on this problem…

Which is why I need a valve tester – it is very important to be able to test and choose the valves that I want to use in my designs.
So it is good to talk to others about different valves and design.
You see, at the moment I cannot work, I can only talk!

Regards

Karl
PS Peter, what are you doing in Bulgaria?

[Peter_C64]

Hello Karl,
Here is a picture of the main board after transfering the laser printer toner:


You can see there is only one track that is not transfered well. And after some retouche with a CD marker:


The idea is to use high quality paper and the recommended one is a photo paper for inkjet printers (but we use laser printer!). I have used one brochure printed on a thick glossy paper (we have tons of them in the office) and the only problem was to find a sheet with enough white space. Then I secured the board on the paper with masking tape and heated it up with a hot iron (a vintage one without water).

It will be better to transfer the image on a slightly bigger piece of PCB and cut it after the etching. If you don't succeed the first time it's easy to clear the board with some solvent. I also first sanded the board with a steel wool and then cleaned it with alchohol.

After the transfer I soaked the board with the paper on it into cold water and after some time started to remove the paper. The white stuff on the tracks is some white coating that the quality papers have and the top layer of the paper which seals the toner on the board. The tracks are a little wavy - maybe I had heated it too much but the board is still usable.

Of course the method with photo resist will give better results but I'm not planning to make a lot of PCBs (I'm using handwired turret boards) and wanted to see if it's possible to achieve good results with this simple method.

This is my first PCB since 20 years ago when I worked as a electronic designer (we were using OrCAD for DOS at the time). Now I work in a completely different field (GIS) but I'm interested in valve amplifiers. I've built one 18W Marshall clone that passed through many modifications and now I'm in the proccess of building a second one (it will be a low powered PP amp because the other one is too loud for home use).

I also have some vintage PA and guitar amps that I'm planning to modify. I have wounded one output transformer and would like to try different ways of interleaving in the next ones. I have a source for the wire but it's hard to find lamination in small quantities so I'm disassembling old transformers.

Yes Karl, I like to use vintage parts - caps, resistors, valves and other stuff that is not produced anymore. In this album you can see some of my amps and other parts:
http://s1185.photobucket.com/albums/z357/pch64/

I also want to build the tester because without it I am able only to measure the anode current. It's good to know the Gm and to check the valves for shorts and gas too.

Regards,
Peter

[timohaveri]

I also have bought some DC-DC converters for the heater supply. I was going to make a DC supply using linear regulators but that would perhaps have been impractical with a lot of wasted heat etc.

For the lower voltage ranges, I chose this:

http://www.ebay.com/itm/DC-to-DC-Buc...-/180966353865

The minimum voltage is 0.8 volts so it can power also battery valves. Some other converters go only as low as 1.5 volts. The current capability is more than enough but at least it can handle the big valves too. The size of the board is quite small.

For the higher ranges I chose this:

http://www.goodluckbuy.com/index.php...oduct_id=87546

Again it is rated with way too much current but it was the only that I could find that goes up to 80 volts. In fact when I tested it, I discovered that it goes up to 100 volts and even more but I didn't go there because the output capacitors are only rated 100 volts. Also some other components seem to have only 100 volt ratings.

This way I can have almost the same heater voltage range than the actual AVO meters. I don't know if I'll ever need the highest voltages but one never knows.

[miludeca]

Hello everyone,

New to the forum and just thought I'd say hi. I came across this website and this particular forum when I was researching used valve testers. Looks like I may end up building my own after everything I have read on here!

Cheers,
Mike

[mikeydee]

Gosh a lot has happened on this thread since I was last here. I thought I was signed up for notifications but apparently not. I can't believe that a year has gone by and my progress has been pitiful.

My build is around an aluminium case with a panel cut out for the knobs etc
I plan to use a technique called Lazertran for the front panel which is apparently a cheapo version of silk-screening.

I was wondering what other had used for connecting the boards together. I started off thinkging I would but some molex pins but they, or rather the tool is so expensive. I might try the D connector as per TopCap but it looks a little fiddly. Any ideas?

PS Thanks ColinTheAmpMan by the way for responding to my query on cables about a year ago. I am sorry not have replied sooner.

Mike

[Refugee]

I would select a tool first and then adopt a connector range to fit it.
http://uk.farnell.com/molex/63811-10...ool/dp/1703928
Add the shells and pins and a small number of other things like caps and you will be able to have free shipping.

[Peter_C64]

I finally finished the main board - it's not perfect but not too bad for a home made PCB:


I hope to get the case this week and to continue with the build.

Peter

[edgobb_]

Hello group,

I have been sitting on this project for over a year and have been compiling parts again as of late.

When I contacted our friendly Asia Engineer, Georgio, he told me that he does not carry the DPM with the 200mV AC spec. He then told me that he never carried it.

So, do you kind folks think that I am having a language breakdown, or am listing the incorrect meter? Are all three meters 3 1/2 digits, or was one different?

Thanks so much for all the education while I have remained silent for so long.

Have any others finished their Sussex save the several that have posted their results? Of the seeming 30 to 40 units that could have been started, I'd sure like to hear about some more experiences.

All the best,
Ed G

[Refugee]

I have spotted these low cost DPMs.
They are worth a look at the price.
http://www.ebay.co.uk/itm/Mini-DC-0V...item27c73b5d8e

[Top Cap]

Something to be wary of though with cheap meters:-

Refresh speed: about 500ms/each time.

[ColinTheAmpMan1]

Originally Posted by Ed_Dinning

Hi Karl, on the question of pcb's; it may be possible to obtain the masters or Gerber files of the original units if it can be determined where they were made.

Hi All,
If anyone is actually doing anything about getting pcbs manufactured, then I would be interested in buying one.

Apart from this, I am glad that others have sorted out the apparent fears that I had about the accuracy of the DPMs. On reflection, I think my testing method wasn't rigorous enough. I suspect that the long leads I used were picking up mains hum, or something. It is a relief that others have ironed this out. Thanks.
Regards, Colin.

[mikeydee]

Originally Posted by edgobb_

When I contacted our friendly Asia Engineer, Georgio, he told me that he does not carry the DPM with the 200mV AC spec. He then told me that he never carried it.

Hi Ed G,

I am pretty sure it was georgio that I got my meters from about a year ago. Could be that there are multiple people on that email.

My build has been on ice but has recently got moving again with a lovely Lazertran panel baked in the oven!. I plan to start a build diary thread on a different part of the forum as I read somewhere back that was the right forum-net-i-quette.

Hopefully might be useful as a step by step guide for others like me who are a bit nervous about putting it all together.

Mike

See below mmmm lovely

[edgobb_]

That looks great, Mike! Can you attach a close-up view of the panel? I might be interested in baking up a tasty valve tester panel of my own.

I look forward to following your thread when you get it started.

I got my panel meters in the mail/post today. Just my luck, one of them is the incorrect specification. Another 3 week wait from China is in my future.

I am currently looking for the Hammond enclosure that is available here in The States, and trying to decipher what wattage and composition resistors to use.

Cheers,
Ed

[mikeydee]

Apologies for the delay - missed the prompt. Here is a quick close up of the panel.

Mike

[Top Cap]

I had a problem testing four ECL82's today, all four gave crazy gm figures jumping from 30 to actually causing the gm panel meter to go over scale. I put this down to oscillation but how to stop it. I attempted to wrap a three turn wire loop of 24swg tinned copper wire around the valve envelope, twisting the ends together then connecting this to ground (Cathode). It had some effect but the most startling cure was placing a short 50cm test lead on it to act as an aerial, moving the wire loop up and down the valve envelope for steadiest reading. It seemed to be best placed at the lower part of the envelope. The loop allowed me to take some nice steady fully believable gm figures for all four valves. Has anyone else had problems with parasitics of this sort, anyway the method I used seems to be one answer to it.

[Richard]

Hi everyone

I have been sort of following this thread, but there is so much information, it makes it hard.

As I understand it there is a fully working design, with the occasional issue raising its head like the ECL82s today oscillating.

I am considering building one to update an AVO MkIV
As I see it a lot of the work is done for me, I can use: -
original case with a new front panel
original top panel sockets and selection switches
original LT supply transformers and selection switches mounted on my new front
original supply transformers

Has anyone tried this?
Are there still PCBs available?

All thoughts welcomed

Richard

[mikeydee]

To all fellow sussex builders. I have started a build diary thread https://www.vintage-radio.net/forum/...ad.php?t=90517 to capture my progress and help other making tentative steps along the sussex path.
Please take a look.

Mike

[Top Cap]

That's brilliant Mike and yes it is a challenge to work out the best place for things such that switches do not short to the transformer body etc. Like you, I was concerned about long wires between the switches and valve holders. I had to use a ready made case due to no metal working facility being available to me, all proverbial kitchen table stuff here. The case I used dictated that the only place for the selector switches was along the bottom edge of the case and sure enough the problem of very occasional instability arises for me when testing some high gain valves. Richard, for me this problem rarely occurs and no doubt others with different layouts do not experience this at all. Mike is doing what I did with my Sussex handbook, it is just a record of how I approached the build and I certainly would not fully recommend the case I used as it was, well, very restrictive . But what I have does the job for me, I only have the odd valve to check out and it is great for matching up pairs.
Well worth the money building it.

[Ed_Dinning]

Hi Gents, various techniques to stop oscillation can be used with greater or lesser success.
Try small ferrite beads on the lead to each valveholder pin.

Add say 100R resistors in series with each pin

Try small caps (under 1000pF) from each pin to a good ground.

Problem with all these solutions is the need for a lot of parts as they need to be installed on each valve base as close as possible to the pin. Possibly better to start with B9A, B7G, B8A and Octal as these were the bases for most high gain valves.

Ed

[Dekatron]

You could try a grid stopper resistor for the ECL82's, I usually use a 1K to 10K resistor soldered directly to the valve socket, that has always worked for me in all valve testers I use.

I am using a "break-out" valve socket with a plug that I can re-solder in any configuartion that I need fro troublesome valves, usually pentodes or a combination with one part being a pentode.

AVO used ferrite beads on the wiring on their valve panels and even patented the method, see patent GB735865A in this thread: https://www.vintage-radio.net/forum/...ad.php?t=86837