The "Sussex" Homebrew Valve Tester.

[vidjoman]

Hi Alan. Yes it is from CPC. it's a Camden Boss model RTM 2703. With carefully placement it's possible to get it all in with all the controls etc. on the sloping panel and the valve bases on the top. I've only got the storm damage pictures at the moment but will take more and post later.

[vidjoman]

Pictures of the assembly as it is at the moment. The base is almost finished and the top is just a printout (that got wet) of the layout. The top has been drilled and meter holes cut, the valves go on the top in the blank space. I was in the process of checking all holes are correct before getting a decent print to cover the front panel. I have fitted a hinge so the case can be opened without fear of detaching wires. On the back there are cutouts for a mains input, 2 fuses and a computer fan that sits behind the heatsinks.

[a_strong]

Very nice, I look forward to seeing pictures of the completed item.

I am planning on using a couple of transformers that I already have but since I may have to buy Ed's custom transformer I will have to take a Rain Check on the the Boss enclosure at close on £70.

Regards - Alan

[AmadeusMozart]

Originally Posted by crackle

Rather than switches for the selection of electrodes etc. I was intending to use a patch bay so I could use a short banana plug patch lead to connect supply to electrode. By using this |I thought that if needed I could also insert additional components.

Mike

I am just about to start collecting parts - have written a PM and an email to Martin for the PCB but no reply so suspect he has been too busy.

I also thought about the patch pad and then stopped to think what I normally will be testing in audio gear. Basically this will be some 9 pin pre amp tubes (12A?7, 9 pin power amp (EL84) and some power octal (KY66, EL34, 6V6 etc)

I don't think I really want to start using octal pre so this brings me to three socket layouts. I like the way Steve Bench did his tube tester (the RAT tube tester) where he just wired them all and no switches and am intending to use that one. Make it more idiot proof so to speak. Any other tubes and one should be able to make some adapter based on going into the octal socket.

I also have a hefty shipping charge for anything heavy from other parts of the world and am opting for buck-boost dc-dc converters for heaters. Likely I will be using a 12V to 220V AC inverter and then rectify that for use as HT.

I want to run the lot of 12V so I can take it with me in the car to some secondhand places and test stuff out on the spot. Easy enough at home to have a 12V supply.

[AmadeusMozart]

In http://www.tubeaudiostore.com/tubmatdem.html is explained the difference between mu and gm.

In same article it is mentioned that pentodes should be tested as gm and triodes as mu.

In order to measure the mu we need to have a constant current source. At the moment there is a current limiter in the plate supply chain however if we make this adjustable then we get constant current source.

We then measure AC current instead of AC voltage and we've changed the setup into a mu meter.

Plate voltage constant => measure at the plate the AC current variation = gm
Plate current constant => measure at the plate the AC voltage variation = mu

What does everyone think?

[crackle]

Hi
I always find it helps to have a circuit all in one piece when I am studying it.
I have tidied up and enhanced the image, from the word document, of the complete Sussex VT circuit.
I believe this drawing to be clearer than the original. You can also edit the image and make your own notes in it using an image editor.
Please find the circuit in the attached zip file.

Mike

[Dekatron]

Originally Posted by AmadeusMozart

In order to measure the mu we need to have a constant current source. At the moment there is a current limiter in the plate supply chain however if we make this adjustable then we get constant current source.
We then measure AC current instead of AC voltage and we've changed the setup into a mu meter.

I believe that the RAT-Tester that Steve Bench designed a long time ago uses a mosfet transistor in the cathode circuit to perform this measurement, take a look at the circuit diagram here: http://www.jacmusic.com/techcorner/SBENCH-PAGES/sbench101/RAT_GMMU/gmmu_1.gif (the texts can be found either here: http://www.jacmusic.com/techcorner/SBENCH-PAGES/sbench101/#TubeTest or here: http://triodeel.com/tester.htm).

It should be possible to incorporate this design in the Sussex Valve Tester since they are similar in design otherwise (the Sussex almost looks like a copy of the RAT-Tester to me).

/Martin

[AmadeusMozart]

Steve Bench's RAT tester uses a CCS in the cathode and in that way sets automatically the negative g1 voltage. It has its own set of (potential) problems.

All I am thinking about is to limit the current in the anode feed with a CCS, set the voltage on g1 as per manual and then check the AC voltage (against ground) on the plate.

However the Sussex works fine as is and I might built it without any changes - for the moment the important part is to figure out if a dual triode is matched. Pentode's I can figure out in circuit.

[mole42uk]

Originally Posted by crackle

I have tidied up and enhanced the image, from the word document, of the complete Sussex VT circuit.

Hi,
It might be good to review your drawing and incorporate some of the later mods such as the current limit resistors on the anode supply....

Richard

[crackle]

OK done that;
if anybody is aware of any other approved mods to the original circuit let me know and I will incorporate them.
Mike

[Station X]

Originally Posted by Paul Stenning

Just a thought... Because this thread is now approaching 1000 posts, it would be very difficult for someone considering building the project to find all the key information. The discussion above illustrates the problem.

Perhaps it would be a good idea if someone who knows a lot about the project could create a new thread containing all the important information someone would need to build the valve tester, including circuit diagram, parts lists, PCB and transformer suppliers, operating instructions etc?

If that thread was then just updated when key details were changed (such as an agreed circuit modification) with general discussions remaining here, it would be a really useful reference.

We would of course make that thread sticky. It could possibly be left closed too except when an edit is needed?

Is there a forum member willing to take on or coordinate this project?

[crackle]

Originally Posted by Station X

Is there a forum member willing to take on or coordinate this project?

I dont mind giving it a go, I am still in the process of building my valve tester.
I have plenty of time, but it would be appreciated if members could point out or update me with the "approved" modifications, this will help me find all the information for my own use as well..
I am not confident enough to approve any modifications.
I have already edited the "manual" and corrected what I considered were page layout problems, in particular the list of parts had a lot of rows not visible where they had fallen off the bottom of the page. Was this just me and my version of "Word" or did you all have problems.
I have said I will send this to mole42uk, if he can send me his email, so he can check the new file.
I believe there is a 2nd BOM. Is this a complete one?
Mike

[Station X]

Thanks for your kind offer Mike.

It's probably best if we refer to modifications as "tested good" rather than approved, as I've no idea who the Approval Authority would be.

The are several modifications listed in this thread, although 1000 plus posts is a lot to read through. Anyone want to have a go at identifying the posts concerned?

Also is anyone able to confirm that the new BOM is correct and if not, what's missing?

[KeithsTV]

I've been following this project with interest over the past 4 years and agree that is a credit to Mike the original designer. As has been said it can be a daunting task to read over 1000 posts to find the relevant information so the idea of co-ordinating all the relevant information is a good one.

I would therefore like to offer my services to help co-ordinate all the information and produce a manual for the tester to cover the circuit, pcb layout and use of the tester.

I don't think it would be a quick process as there is a lot of information to digest and arrange into a form that is easily understood and error free.

Let me know what you think.

Keith

[Pamphonica]

Keith, I think that is a noble offer - are you sure you know what you are taking on?
But I know it would make a huge difference to the success rate of Sussex builds. Mine is half-done (long process!) and I am already losing track of which mods I need to retrofit.
Thank you for offering.
- Jeremy

[mole42uk]

Hi Keith,

A Herculean task!

However, if you decide to accept it, I am willing to do some proof-reading and/or editing to help you.

Best,
Richard

[KeithsTV]

Agreed it is a big task but I have a few ideas to make the manual more useful to builders and users. I'll read through the whole thread and extract any relevant information regarding circuits, suppliers etc before starting to edit it.

As an aside about 13 years ago I was part of a team producing a photographic record of the village we lived in. I ended up processing about 800 pictures and editing the final book which was well received by the team and the village.

Anyway this will give me something to do during my lunch times at work and Richard I'll be in touch regarding proof reading etc.

Keith

[crackle]

Hi Keith
As I mentioned I have done a little work on the circuit and added the new value resistors for the anode current limiter and removed much of the JPG artefacts. I have also edited the manual document, only changing the layout and tables so all the rows show.
Rather than posting them on here, If you PM your email address I will send them to you.
If you want any more help with improving graphics please let me know.
Mike

[mikeydee]

Originally Posted by mole42uk

I think I finally cracked the problem with my Sussex and EL34s.
Putting a scope on the anode voltage I found that it oscillated madly when testing any EL34. Putting my hand around the valve (before it got too hot!) stopped the oscillation and the meter readings became steady.

Blimey! What fantastic news. I only just saw this two months late but really glad you posted it. I will try the same on mine.

[vidjoman]

Latest on my front panel.
The printing was on A3 thin card and glued to the aluminium panel and then covered in clear sticky backed plastic sheet. (meant for covering book covers)
The parts are fitted, but no wiring as yet. The back has a mains inlet, 2 fuses and a computer fan.
I've decided to add some small 10 amp relays (cost about 75p each) for the heater voltage selection to avoid the possibility of damage to the rotary switch passing a higher current than specified and also for the switch to link direct/indirect heater cathode wiring.