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swordholder 24th Dec 2009 8:57 am

The "Sussex" Homebrew Valve Tester.
4 Attachment(s)
Moderator notes:-

The manual (as of May 2014) is available here:-

This manual supersedes the documents below (however the links remain for reference).

A handbook for this tester can be found here:-

The circuit can be found here:-

Printed circuit boards are available here:-

Transformers are available from forum member Ed Dinning:-

A Bill of Materials can be found here:-


Hi All,
I have designed and built a valve tester just to prove to myself that I could, also to keep the old grey cells going (I am an OAP).
This is a fairly universal type which cover 6.3v valves on the common B9A, B7G, and octal bases as used in the majority of audio and radio receivers.
Anode and screen voltages are switched DC fed from a pair of current limited FETs, Grid voltage is variable, and is monitored on a panel mounted DVM.
Anode current is displayed on a second DVM. Gm is measured on a third DVM and is measured by reading the voltage on a sensing resistor in the anode. Signal being applied to the grid.
Heater continuity, cathode heater and inter electrode shorts indicated by LEDs on the front panel.
Total cost (apart from the case and mains transformer) I would estimate at around 50 buying new components.
I used DVM modules (bought from China on E Bay at around 6.50 each) as they dont require range switching and are nowadays comparable in price to moving coil meters.
if anyone is interested I can post the circuit etc on the forum.

David G4EBT 24th Dec 2009 9:35 am

Re: The "Sussex" Homebrew Valve Tester.
Fantastic Mike!

A well conceived design from a professional engineer with expertise in valves is bound to be of huge interest on the forum. Valve testers now command a price beyond that which is cost-effective for the occasional testing of a few valves, but your design - even with new components, is within the pockets of most enthusiasts.

I agree about the little DVM modules from China - I've used a 500V one for the capacitor reformer which featured in Bygones and the BVWS bull - cheap as chips (pardon the pun!).
I think you'll find that this thread will have a longer run than "The Mousetrap"!

Why not write it up as an article in the BVWS Bull, or Radio Bygones?

Welcome to the forum Mike - if my memory serves me well, I recall correspondence with you some years ago (maybe on packet radio?) re the ill fated off-air timebase for the PW Robin frequency counter, which PW botched through printing errors. My Robin is still doing sterling service!

Thanks once more for such an innovative design for the valve-tester.

Stand by to be deluged!

Best regards,


MichaelR 24th Dec 2009 9:45 am

Re: Homebrew Valve Tester
Hi Mike,

I have downloaded your circuit to study in detail but as with David I commend you in having produced what will be a very useful piece of gear.

I look forward to this thread being a long and interesting homebrew project.

Merry Christmas to you and you David for all the very interesting technical snippets you provide.


igranic 24th Dec 2009 1:25 pm

Re: Homebrew Valve Tester

Outstanding! Worthy of a blow-by-blow write-up, if you feel inclined.

The PCB looks really professional. Did you make it yourself? What tools/facilities did you use?

Would you be able to post some pictures of the front panel and the valve socket panel?

Incidentally, what are the device types of Tr1 -Tr5 ?


swordholder 24th Dec 2009 2:41 pm

Re: Homebrew Valve Tester
I made the PCB myself using photosensitive board and inkjet film for the transparancy. I used an old DOS version of boardmaker to produce the layout and diagrams. Holes drilled using a hobby pillar drill.
The front panel was produced using MS Publisher and this was fronted using 4mm perspex.
TR1 is an MPSA92, TR2/4 are BUZ80, TR3/5 are MPSA42.
I will post photos of the top panel after Xmas (I doubt anyone will be doing much tomorrow), and also PCB tracking and layouts if anyone is interested.
Incidentally, I forgot to mention that the 9 switches on the top panel are used to configure the pins inthe same way AVO do it, in fact the numbering corresponds to the AVO CT160 configuration. 1 = cathode, 2/3 = heaters, 4 = grid etc.
The only tools I used were normal hand tools, power drill and Q Max cutters for the valve bases.
I hope that answers your questions.

swordholder 27th Dec 2009 8:54 am

Re: Homebrew Valve Tester
3 Attachment(s)

Here as promised are some photos of the valve holder panel and the front panel.
Fortunately the case I used was 300mm wide, so I could use A4 paper for the front panel (I ignored the 1.5mm difference either side - homebrew engineering tolerence!!) as it was a simple solution to getting a decent looking panel.
Although the wiring looks a nightmare, use coloured wiring (Rapid Electronics do small packs of both solid and multi core wire) and wire up each colour in turn.
If anyone is interested, I can do printed circuit diagrams, but I woukld like these to be used only for pivate NOT COMMERCIAL use without my permission.


David G4EBT 27th Dec 2009 9:42 am

Re: Homebrew Valve Tester
Mike, I have to say again that this project is so outstanding that I do hope you'll write it up for publication in either the BVWS Bulletin of Radio Bygones. The topic of valve testers and testing valves crops up with regularity on the forum, and your tester would make both an enjoyable project in its own right, and cost effective too.

The use of a PCB aids repeatability, and as you've pointed out, though the valveholder wiring looks a complicated "rats' nest" in reality, it's really quite simple. (Just one valveholder could be wired up first to make sure all is well, then others progressively wired up later).

All of the components are readily available too.

You've already done most of the writing up which would form the basis of a magazine article the in your postings on the forum! Two projects which were very well received have been the Electrolytic Capacitor Reformer, which featured in both Bygones and the Bulletin, and the Raymond Haigh Wobbulator. Your valve tester would be a most worthy item to complete the trio!

Best regards,


MichaelR 27th Dec 2009 11:37 am

Re: Homebrew Valve Tester

Originally Posted by swordholder (Post 294685)
If anyone is interested, I can do printed circuit diagrams, but I would like these to be used only for private NOT COMMERCIAL use without my permission.

Hi Mike,

I am interested , I would like to build a unit.


swordholder 27th Dec 2009 11:47 am

Re: The "Sussex" Homebrew Valve Tester.
I don't belong to either of the two organisations, as an OAP funds are limited!!
I am happy to do a write up and put it on this forum, but I would feel cheated if someone else used my design for financial gain. After all I am sure you appreciate quite a lot of work has gone into it.


swordholder 27th Dec 2009 11:49 am

Re: Homebrew Valve Tester
Thanks for the interest,
I will post the printed circuit diagrams in the next couple of days.


Station X 27th Dec 2009 12:10 pm

Re: Homebrew Valve Tester
Magazines are always on the look out for contributions and they generally pay for them. An email to sound out editors might be a good idea.

Regardless of where the design is published it would be difficult to stop it being used for commercial gain.

David G4EBT 27th Dec 2009 12:29 pm

Re: Homebrew Valve Tester

Originally Posted by swordholder (Post 294721)
I don't belong to either of the two organisations, as an OAP funds are limited!!
I am happy to do a write up and put it on this forum, but I would feel cheated if someone else used my design for financial gain. After all I am sure you appreciate quite a lot of work has gone into it.

I don't think you need to be a BVWS member to submit articles for consideration, and Radio Bygones is a commercial magazine (available only by subscription). I just think that your project is so well conceived and designed, that it would be a great shame for it not to be more widely circulated among enthusiasts than on the forum.

Both organisations are always pleading for articles in any format from hand-written, on a floppy, CD or whatever, and this project is up there with the best.

If anyone is to gain commercially from such an excellent project, however modest the recompense, then surely it should be the designer (in this case, a self-professed impecunious "OAP"!), from whatever the going rate per page of manuscript is paid!

In the case of Bygones, they'd probably arrange for PCBs to be made if sufficient demand.

Go for it would be my advice!



MichaelR 27th Dec 2009 1:07 pm

Re: Homebrew Valve Tester
I am sure Paul Stenning can confirm how to approach this but if you published your work on the forum it can be worded such that you maintain total copyright.

I am prepared to pay for any information you provide to me to build it anyway and of course would not infringe your copyright.

A good project


XTC 27th Dec 2009 3:01 pm

Re: Homebrew Valve Tester
Unfortunately, I believe there's very little you could do to stop commercial exploitation you don't approve of.

You have copyright on any articles you may write describing the tester. You also have copyright on the PCB layouts. You couldn't stop people writing their own articles about the circuit with their own version of the cct diagram and doing their own PCB layout. You don't have a copyright on the concept of the circuit, just your particular expressions of the circuit as diagrams. Were it a microprocessor based project, you would have a copyright on the firmware, but copyright wouldn't stop white room reconstructions of the firmware, because copyright wouldn't protect the concept of what the firmware was doing, just your expression of it.

The other approach is patents. I recall it costs about 15 grand to register a patent. Certain tests have to be passed to qualify. The invention has to be unique, non-obvious, no prior art. If you are granted a patent, it gives you a time (15 years I think) in which you have a monopoly on commercial exploitation. You can sell the patent, license production under it, and take action against infringement. I don't think you can stop people making the device for themselves - that is non-commercially.

Check it with a lawyer, but I'm pretty sure this is right.

I'm sure the best course is to write this project up as an article for Radio Bygones, or similar, as others have suggested.


Station X 27th Dec 2009 3:11 pm

Re: Homebrew Valve Tester
Don't waste time or money patenting anything. Unless you have loads of money for legal fees it's impossible to protect a patent. That's why most small inventors licence their product with a big manufacturer who has enough money to protect their interests.

VHFHerald 27th Dec 2009 3:15 pm

Re: Homebrew Valve Tester
Excellent work, Mike.
You may be aware, Steve Bench did a similar thing a few years back.

David Simpson 27th Dec 2009 3:49 pm

Re: Homebrew Valve Tester
Mike, or should I say Santa - has given Forum enthusiasts a fantastic Christmas present.
AVO & other quality old VCMs are fetching silly money on the internet. However, this simple tester, which provided better DC sourced electrode voltages, is truely a masterpiece of ingenuity - at such a relatively small outlay.
As a guy who has banged on about CT160's in the past, I humbly take my hat off to you Mike.
I would echo other folk's suggestions regarding voluntary donations to Mike for email attachment downloads, or postage of circuit & construction details. Not for me to say, but prahaps the Forum Moderators or BVWS Management might consider some sort of financial negotiation with Mike.
Trouble is, now that this article is in the public domain, any mercenary commercial constructor can hijack Mike's great design.

Regards, David

swordholder 27th Dec 2009 5:16 pm

Re: Homebrew Valve Tester
Many thanks for comments and support.
Over the next few days I will get together a write up and the PCB foil patterns and component layouts, together with setting up instructions and voltage readings from my prototype.


ppppenguin 27th Dec 2009 6:57 pm

Re: Homebrew Valve Tester
Is there any real risk that somebody will exploit the design for significant commercial gain? Is the shortage of valve testers bad enough that it would be worth somebody's while setting up a production run? In both cases I rather think not. There are other designs already in the public domain, notably the RAT I haven't noticed a rush to exploit them commercially.

I'm sure that Carl Glover (BVWS Bulletin editor) would be delighted to publish your design, even though you are not a member.

Michael Maurice 27th Dec 2009 10:38 pm

Re: Homebrew Valve Tester
This is truly excellent,

May I suggest that if you want to earn some money out of it, you produce it in kit form.

You'll of course have to give step by step instructions as to how the wiring is done, and you'll be supplying all the parts to make it.

You probably wont make a fortune from it, but it could in someway help you.

Once again, a splendid idea.


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