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-   -   The "Sussex" Homebrew Valve Tester. (https://www.vintage-radio.net/forum/showthread.php?t=48853)

swordholder 24th Dec 2009 9:57 am

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

The manual (as of May 2014) is available here:-
https://www.vintage-radio.net/attach.../sussex-v1.zip

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

A handbook for this tester can be found here:-
http://g4cnh.com/public/Using_the_Sussex_VT1.pdf

The circuit can be found here:-
https://www.vintage-radio.net/forum/...postcount=1006

Printed circuit boards are available here:-
https://www.vintage-radio.net/forum/...&postcount=926

Transformers are available from forum member Ed Dinning:-
https://www.vintage-radio.net/forum/...&postcount=768

A Bill of Materials can be found here:-
https://www.vintage-radio.net/forum/...&postcount=974

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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 10:35 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,

David,
G4EBT

MichaelR 24th Dec 2009 10:45 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.

Mike

igranic 24th Dec 2009 2:25 pm

Re: Homebrew Valve Tester
 
Mike,

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 ?

Edward

swordholder 24th Dec 2009 3:41 pm

Re: Homebrew Valve Tester
 
Edward,
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.
Regards
Mike

swordholder 27th Dec 2009 9:54 am

Re: Homebrew Valve Tester
 
3 Attachment(s)
Edward,

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.

Mike

David G4EBT 27th Dec 2009 10:42 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,

David,
G4EBT

MichaelR 27th Dec 2009 12:37 pm

Re: Homebrew Valve Tester
 
Quote:

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.

Mike

swordholder 27th Dec 2009 12:47 pm

Re: The "Sussex" Homebrew Valve Tester.
 
David,
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.

Regards
Mike

swordholder 27th Dec 2009 12:49 pm

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

Mike

Station X 27th Dec 2009 1:10 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 1:29 pm

Re: Homebrew Valve Tester
 
Quote:

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!

Regards,

David,
G4EBT

MichaelR 27th Dec 2009 2:07 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

Mike

XTC 27th Dec 2009 4:01 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.

Pete.

Station X 27th Dec 2009 4:11 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 4:15 pm

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

http://greygum.net/sbench/sbench101/#TubeTest

David Simpson 27th Dec 2009 4:49 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 6:16 pm

Re: Homebrew Valve Tester
 
Guys,
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.

Regards
Mike

ppppenguin 27th Dec 2009 7:57 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 http://www.triodeel.com/tester.htm 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 11:38 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.

Michael

David Simpson 28th Dec 2009 5:09 pm

Re: Homebrew Valve Tester
 
Mike, I would echo Michael's suggestion regarding a kit. And in fact, as an old analogue guy who should really update his working knowledge on modern electronics, I would willingly cough up some dosh for a kit + working instructions. Would be a very interesting project for 2010.
What a difference between the Ferranti145 my nose is presently stuck inside, or the Black Box on the shelf awaiting some TLC.
I would rather money be paid to a retired chap like Mike, than to some far-eastern business producing kits sold in a magazine or on the internet.

Regards, David

igranic 28th Dec 2009 10:15 pm

Re: Homebrew Valve Tester
 
Mike,

Thank you for posting the pictures and for the additional information. My apologies for not responding earlier; festive duties called!

Your endeavors have produced a really professional and functional looking tester, and the three digital meters seem to give all the essential functionality of a commercially produced VCM.

I would like to add my congratulations, and hope you feel able to carry this project forward for the benefit of yourself and other enthusiasts.

Edward

G8UWM-MildMartin 29th Dec 2009 2:12 am

Re: Homebrew Valve Tester
 
That's an extremely elegant design.
And a stroke of genius to make it compatible with the AVO VCM settings!

If I hadn't acquired an AVO VCM at a very reasonable price decades ago, I'd definitely want one.
And I'd still be tempted to build one if a kit came out...

I'd like additional filament/heater voltages of 1.4-117V, though.
I could wind a vaguely-suitable transformer from my Louth kits, same tappings as the AVO, but could you (or anyone else) perhaps design a switch-mode regulator to suit, please?

Congratulations again,
Martin.

Ed_Dinning 29th Dec 2009 9:45 am

Re: Homebrew Valve Tester
 
Hi Martin, bit of a wide range for an SMPS, also given the current requirements fos some rectifiers. Linear would do it but double up as a room heater.
If you want SMPS it would be better to go for about 3 or 4 ranges from transformer taps and control of volt between them.

Ed

swordholder 29th Dec 2009 9:55 am

Re: Homebrew Valve Tester
 
Hi All,
Thanks to everone who has posted a comment. My intention is to post the PCB details shortly.
I will not do a kit of parts, most are readily available from Rapid Electronics, and I do not have the resources to either finance or store them. The mains transformer is possibly one fly in the ointment, although there must still be many of the "replacement type" transformers around in junk boxes which is where mine came from. No particularly difficult to get parts are used.
My main interest is Audio (Vintage and modern), the tester meets all my requirements. I dont want to get into modifying the design, I'll leave that to others. It should be fairly simple to accomodate different heater voltages, simply add another filament transformer and use that instead of the 6v winding on the existing transformer.
I don't want to get into producing PCB on a large scale, as I'm not now able to easily drill the holes to the accuracy I would expect to receive myself. Anno Domini strikes.
I will submit the design to the BVWS with a full write up to see if there is any interest in publishing it. If any of the BVWS team read this perhaps they could send me a PM and let me know what they want.Thanks to everone who has shown interest, the response has been quite overwhelming.
Regards
Mike

swordholder 29th Dec 2009 2:11 pm

Re: Homebrew Valve Tester
 
2 Attachment(s)
Hi All,
Here is the PCB tracking and layout attachments.
The eagle eyed amongst you may notice some small differences between the layout and the photos. This is because I modified the original board, mainly adding a capacitor across the anode current sensing resistor and allowing a larger GM sensing resistor.
I havent built up the current board, although I have checked and re-checked the tracking I would recomend that you check for any errors yourself before etching. From past experience it is easy to overlook an error no matter how many times you look.
You will see that the LT mains transformer has no tracking connected to the pads. It seems that each manufacturer has their own pin connections, although most work on the same grid pitch. I have tried to make this as universal as possible, so connect links from the 240v input to the relevant pads on the transformer, likewise the secondary.

Omegaman 1st Jan 2010 3:14 pm

Re: Homebrew Valve Tester
 
Hi Mike,

Your valve tester is a fantastic project and if you have no objections, I would like to build one for myself.
I wonder if you could clarify a few points on the circuit diagram for me. Please excuse my ignorance if these points are obvious and I have missed them!!

ZD11 & ZD12. Are these the same 15v types as in the anode voltage reg.?

In the anode voltage reg. should there not be a resistor to ground from the junction of ZD9 cathode and R5 to provide a ground reference?

What FSD/meter types did you use for the 3 panel meters? I gather the grid volts meter is DC volts but I'm not sure about the other 2.

What value is C10 (Across the grid volts pot)?

What type is D6?

I intend to wind a transformer to give all voltages required from one unit and also to use a multipole switch to select each of the common types of valve I use rather than the 9 switches like the AVO. My VCM163 will be resigned to the shelf now!!

Kind Regards

Howard

swordholder 1st Jan 2010 10:45 pm

Re: Homebrew Valve Tester
 
Howard,
Thanks for the comments, very much appreciated.
All the 15v zeners are the same (If I remember correctly 1W rating)
There is no bleed resistor in the anode circuit as the load resistor is the valve itself, no HT is applied until the fuctions switch is in the test position.
The meters I used are
200v DC for the Grid voltage
200mV DC for the anode current
200mV AC for the GM meter
I bought these from
http://stores.ebay.com/Runfunpower
Note these have to be run from separate 6v AC supplies or they will be damaged.
C10 is 100uF 63v
D6 is 1N4148
Hope this answers all your questions
Kind regards and a Happy New Year

Mike

glowinganode 1st Jan 2010 11:15 pm

Re: Homebrew Valve Tester
 
Mike, thanks for taking the time to publish this design.
I wonder if you might clarify / confirm a few points, as I'm not sure if I understand this circuit totally.
The Anode current meter is a DC Voltmeter, with a 1 ohm shunt the display reads directly in in Amps. This seems slightly insensitive.
The GM meter is an AC Voltmeter, with a 10 ohm shunt. Each displayed unit equates to 100mA of superimposed AC. If a 5mA/V valve were being tested, then to get a reading of 5.0 on the display would require 500mA's of superimposed AC, and 100 Vac signal on the grid. This seems too high. Also should the voltage across the shunt be AC coupled to the meter as it has DC component too.
The DVM modules I've used in the past require a DC auxilary supply of around 12 Vdc, assuming yours are the same, where do you obtain this from as both the above meters are at Anode potential.
I'd be inclined to decouple the Screen and Anode supplies after the S/R's to reduce any tendancy of parasitic oscillations, and to reduce the output impedance of the Anode supply appearing as additional Anode load which might cause inaccurate GM readings.
I am currently building a Valve tester and would like to incorperate parts of your design as you have obviously put a lot of thought and effort into yours.
I've used a small audio output transformer in reverse to measure the Anode AC component, as this gives a reasonable signal level from a low apparent impedance, removes the DC component, and isolates it from the HT so the metering circuit can be at ground level. I've experimented with a band pass filter (2KHz - GM test frequency), to reduce the effect of ripple and the amount of HT smoothing required.
Many thanks in advance, hopefully your advice will help resume a stalled project.
Rob.

P.S. I've just read your reply above which you must have posted at the same time as me. I assume the meters are scale 0 - 200mA, and 0 -20mA/V, with 1 Vac on the grid (you might find this is a little high for some valves). It's quite easy to modify these DVM modules to get the required D.P. to illuminate with a suitably placed resistor.

swordholder 2nd Jan 2010 9:33 am

Re: Homebrew Valve Tester
 
Rob,
I'll try to answer your points. The anode current meter is indeed a shunted voltmeter, a resitor of 1 ohm will generate 1mV when 1mA is passed through it. The 200mV module (actually 199.9 mV) will actually read to a resolution of 0.1Mv , current can be read to 0.1Ma . Tested an ECC83 and read anode current of 1.8Ma.
I use approx 100mV of audio on the grid, Similarly, the AC Mv meter reads to 0.1Mv and the ECC83 reads 1.7 mA/V.
The modlules I used will operate from 6v AC so admittedly the transformer winding is at HT, but so far no peoblems, and I dont Anticipate any. The modules are well insulated from the panel. Go to the website and have a look at the pictures.
I did think about a transformer in the anode like AVO do with the VCM163, but decided repeatability would be a problem, and I'm not too sure how a small transformer woiuld react to constant DC. Would it saturate the core? plus of course a resistor is cheaper.
Do you run your tester from DC like mine? It may be possible with your design that the transformer is picking up hum from the mains transformer giving false readings.
In my design, the GM meter which is running all the time reads zero for 99% of the time with an occasional flick to 000.1, which may be the zeroing of the meter itself. Nothing to get worked up over.
Hope this answers your questions
Regards
Mike

Omegaman 2nd Jan 2010 4:54 pm

Re: Homebrew Valve Tester
 
Hi Mike,

Many thanks for your reply and the clarification of those points.

I'm going to order some meters next week and get on with it!

If it's ok to do so, I would like to show my efforts later on in the thread when I complete my project. I don't know if that follows the etiquette of the forum?

It would be nice to see other members versions of the project too.

Kind regards and happy new year!

Howard

glowinganode 2nd Jan 2010 8:55 pm

Re: Homebrew Valve Tester
 
Quote:

Originally Posted by swordholder (Post 296164)
Rob,
I'm not too sure how a small transformer woiuld react to constant DC. Would it saturate the core? plus of course a resistor is cheaper.
Do you run your tester from DC like mine? It may be possible with your design that the transformer is picking up hum from the mains transformer giving false readings.

Thanks for your reply. In response to your above comments, the transformer I used was from a 2W single ended audio amp, so it's designed with an air gap to cope with the standing DC. Since I'm using the secondary in the Anode circuit, the amp*turns is nowhere near enough to cause saturation. In a test setup, I varied the DC current from zero to 500mA with no noticable variation of amplitude or waveform of the AC signal. This setup was done on the bench, running off the bench PSU so it wasn't picking up stray magnetic field from a nearby tx. In fact I didn't actually have a problem with HT ripple since my bench PSU is very good. I wanted to simplify the power supply in the tester, without all the complication of a stabilised circuit. I just though it might be a problem, so I considered alternative solutions.
Thanks again for your time.
Rob.

swordholder 3rd Jan 2010 9:38 am

Re: Homebrew Valve Tester
 
Howard,
I'm sure that there will be no objections to posting your tester on the forum. I certainly don't have any, it will be interesting to see other peoples efforts. My layout was dictated by an available case.
When you order the meters, be a bit cheeky and make an offer for them, one one occasion I got one for 6, buying 3 you may get them even cheaper, after all every penny counts!!
The last one I ordered came in 7 days, superb service.
Good luck with the build
Mike

qualityten 7th Jan 2010 6:40 pm

Re: Homebrew Valve Tester
 
As somebody who is very much a learner, and who would like to own a valve tester, this project interests me too.

Howard, may I request that you record your build experience in as much detail as possible to aid those who may be inspired to follow. I agree with others who have said that this looks to be an important resource for forum members. My thanks too to Mike for sharing his expertise with us.

David

Omegaman 9th Jan 2010 4:41 pm

Re: Homebrew Valve Tester
 
Hi Everybody,

Mike, thanks for your permission to use your design.
I'll try to get some meters ordered very soon. I need an extra 2, so will try the "offer" method to see if I can save a bit! I intend to add meters to monitor cathode & screen current too.

David, I would love to attempt to document a build and post it here. I hadn't thought of that. The only problem is, I can be a bit busy at times and may not get to post as often as I would like.

A question for the Mods.
Not wishing to hijack Mikes thread, would it be the correct thing to do to start my own when the time comes, or is it ok to add to this thread thereby keeping all the info together. If I start a new one, which category should I use? Success stories or Homebrew?

Cheers

Howard

Omegaman 9th Jan 2010 5:34 pm

Re: Homebrew Valve Tester
 
Mike,

I forgot this in my last post.

You mentioned in one of your earlier posts that you have some setup instructions and voltage readings from your unit.
Any chance of you being able to post these?

Regards

Howard

swordholder 9th Jan 2010 7:37 pm

Re: Homebrew Valve Tester
 
Howard,
I think that most people (including me) will be interested in any mods you carry out, perhaps the Moderator will indicate regarding starting a new thread or continuing with this one.
Regarding the setting up, I'm not too sure where I stand on that as I have sent the design to the BVWS Bulletin and this will appear in the spring issue.
Perhaps someone from BVWS can advise me on that.

Regards to all

Mike

Station X 9th Jan 2010 9:30 pm

Re: Homebrew Valve Tester
 
I would suggest that any member building one of these testers and wanting to tell us about progress should start their own individual thread in the Homebrew section.

Of course if you finish one, without updating us on progress, post in Success Stories.

This current thread can be used for seeking information from Mike aka Swordholder.

georgesgiralt 9th Jan 2010 9:55 pm

Re: Homebrew Valve Tester
 
Hi !
I may be a bit late on this, but i was far away from home ....
May I suggest something ? Mike can't produce a kit for it's tube tester. OK.
But if someone will gather all parts and propose a kit, I'll be glad to pay for it, including a contribution to the designer. This may pay for a subscription to one or both organizations Mike can't afford and maybe buy some candy ;-)
It will help us get the difficult pieces : the trannies.
If you look at the price a decent valve tester reach these days, I'll be glad to have a very fine kit for a little less than that price and help a fellow enthusiast in the same time ....
What do you think ?

Ed_Dinning 9th Jan 2010 10:01 pm

Re: Homebrew Valve Tester
 
Hi Gents, if there is sufficient interest I can probably arrange to get transformers wound and vacuum impregnated. If I have an idea of the quantities I may get a decent price from my local winder.

Ed

retailer 10th Jan 2010 1:03 am

Re: Homebrew Valve Tester
 
Well done swordholder you stand tall amongst us, anyone that has scratch built something before will know the amount of effort that you have put into your project.
I built a valve tester from a circuit designed by Steve Bench about 6 yrs ago, some readers will know it as the RAT valve tester. I'm a hobbyist not a design engineer so it wasn't a hard decision to use someone else's idea. The RAT tester uses a variable constant current source at the cathode to control the anode current and the valve then sets it's own bias, it does work well. I think that the AVO 163 is able to use either variable constant current source or variable grid bias to test valves.
I had planned to wire the valve base setting switches so that the AVO data manual could be used, but decided that it wasn't entirely a good idea. I can't recall exactly what the problem was but it may have been peculiar to the RAT tester circuit only.
The 200mV AC panel meter that you've used looks very good, I didn't know of their existence 6 yrs ago and had to make my own. I'll look forward to reading the full HOW TO article when you get it done.

Guitarist28 10th Jan 2010 1:37 am

Re: Homebrew Valve Tester
 
Hi all,
This is such a brilliant piece of work that I would rather spend money building a practical and up to date item of equipment than invest in an old valve tester (and to learn from the building of it too).


Well done and lets hope that this is a highly successful project.

MichaelR 10th Jan 2010 2:44 am

Re: Homebrew Valve Tester
 
Quote:

Originally Posted by Ed_Dinning (Post 298013)
Hi Gents, if there is sufficient interest I can probably arrange to get transformers wound and vacuum impregnated. If I have an idea of the quantities I may get a decent price from my local winder.

I will have one ED

Happy New Year to you

Mike

swordholder 10th Jan 2010 9:30 am

Re: Homebrew Valve Tester
 
Ed and others,
If you are going to get a transformer wound, may I make a couple of suggestions.
Don't bother with a 250 - 0 - 250 winding, make it a single 250v one and use a bridge rectifier, I could redesign the PCB to include the 2 extra diodes if required.
Include the 30v winding for the LT supply.
Include the 3 x 6.3v windings for the DVMs
It may be worthwhile to have a multi-tapped heater winding to include 4v valves etc.
If you are testing directly heated valves, an extra switch will be required to connect one side of the heater to 0v. This will of course mean that the C/H LED will stay alight unless a second pole on the switch disconnects the LED.
I realise that the cost of a custom wound transformer depends on the number of windings, so it may not be financially viable to replace the LT and DVM transformers.
What do other members think?
Regards to all
Mike

Mike Phelan 10th Jan 2010 10:04 am

Re: Homebrew Valve Tester
 
I've only just found time to look at your design in detail and read this thread; I would have been very tempted to make this if I did not already have a CT160.

Well done, and certainly worth publication. :thumbsup: :thumbsup:

AmadeusMozart 10th Jan 2010 11:46 am

Re: Homebrew Valve Tester
 
I have just completing collecting all the parts for the RAT tube tester when someone pointed out to me this thread. The RAT tube tester is based on a CCS in the cathode lead and this results in lower g2 and anode voltage as measured to the cathode which I was going to change to using a negative grid voltage. The advantage of the CCS is that it is easier to adjust.

I would make two changes and this is based on observations I made while restoring some Mercury 1000 tube testers and feedback from someone else who has the RAT tester.

The first one is that I would use some ferrite beads at either tube tube sockets or at the switches to try to prevent parasitic oscillation. The second would be to use a setup for valve sockets like the Mercury 1000 / 2000 is using (circuit diagrams are to be found on the web). What is done in these valve testers is to have multiple sockets for the same base but which have different filament connections. Then hardwire the filament connections and do not connect the pins that have a filament connection to the switches. In that way a short of the filament across the switch is avoided (basically that position on the switch for that particular tubebase is n.c.).

There are only something like 4 different filament connections for the Octal and 4 for the Noval and 2 for the 7 pin. The Mercury 1000 has only 2 for the Noval. A worthwhiloe safety measure!

I am using 10 turn bourns pots for the voltage adjustments and am using a 5 A, 15 V variac (that I found on a local auction website) for the filament adjustment (have a 15 V winding on the transformer). This will allow me to drop the voltage on the filament and see the corresponding drop in transconductance which is an indication of how much life in the tube is left (see the RCA tube manual on this).

Anyway this is an elegant solution and I like the layout of the whole. Just wish I could get a similar cabinet locally, my metal working skills are not that wonderfull.

Thanks for publishing and congrats on making something so good looking, well done.:clap:

AM

Guitarist28 10th Jan 2010 12:23 pm

Re: Homebrew Valve Tester
 
Quote:

Originally Posted by Ed_Dinning (Post 298013)
Hi Gents, if there is sufficient interest I can probably arrange to get transformers wound and vacuum impregnated. If I have an idea of the quantities I may get a decent price from my local winder.

I would like one too please Ed

Thanks

Rob

Ed_Dinning 10th Jan 2010 9:10 pm

Re: Homebrew Valve Tester
 
Hi Gents, I'm talking to Mike to see if there are any other features he would like to see on the transformer and I'll get something costed out when this is complete.

Best regards, Ed

swordholder 10th Jan 2010 10:20 pm

Re: Homebrew Valve Tester
 
Hello All,
Ed has asked me what windings to put on the mains transformer.
I have opted for a 250v 100ma secondary (use a bridge rectifier)
3 windings for the DVM (6v)
LT -ve winding 30v.
Withe regard to the heater voltage would any prospective builders reply WITHIN THE NEXT 7 DAYS their requirements.
Please bear in mind that only the most popular voltages can be catered for (ALSO REMEMBER THAT THIS HAS TO BE SWITCHED AND THAT NORMAL SWITCHES CANNOT SWITCH HIGH CURRENTS AND ARE ALSO LIMITED IN THE NUMBER OF WAYS)
Please also bear in mind that the cost of the transformer will undoubtably rise with each heater tap.

Regards
Mike

MichaelR 11th Jan 2010 12:33 am

Re: Homebrew Valve Tester
 
For me 6.3V is adequate.

Regards
Mike


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