The "Sussex" Homebrew Valve Tester.

[ahjohn002]

Hi All,
Glad to know that this thread is alive and well.
John

[David G4EBT]

Although I'm not building the Sussex, I am using a digital panel meter for another project I'm building, which looks identical to those used in the Sussex. The meter arrived today from China, and warns that you must not use a common earth for the measured power and the power supply to the meter.

To quote verbatim:

"Warning: The working power and the measured power can't use one power system together. When LCD meter uses DC working power, must use the isolated power suplly, can't be sharing the power for meter. Wworking power and meter power can't use common ground wire, otherwise meter will be burnt. The meter power must be 9 - 13.5V, if greater than, then be burn".

So there you go then - "no crash and burn = no common ground"!

Oddly, it also says "meter power AC/DC: No +/- differ".

I can understand that on AC, but it seems odd that it infers that even on DC, the power supply to the meter isn't sensitive to polarity. I haven't tried to pwer it up yet - the colour code of the wire doesn't give much of a clue - brown and red is meter power, orange and yellow is measured power.

The one I've bought is scaled 0 - 199.9V DC. (It's for a zenner diode tester project).

I know it's a bit off-topic from the Sussex, and haven't studied the circuit to see what the power supply arrangments are to the meters, but they obviously work OK as Mike has proven.

I guess these Far East meters are fairly generic - the type I've obtained is a "D69" - they come in a range of scales, up to 500V AC or DC, and up to 2 Amps. The last one I bought was a 500V one for the Capacitor Reformer project which featured in Bygones and the BVWS Bull.

I did squirt more than 500V into it, and - as our inscrutible friends advised, sure enough, it did "burn", so I sent for another and was more careful with that one!

Regards, and best of luck to the "Sussex Legionaires"!


David,
G4EBT

[swordholder]

David,
Thanks for that I did realise that, and ED has 3 seperate 6V windings on his transformer. I had previously used one 6V winding on the mains transformer with an extra 2 x 6V transformer.
Regards

Mike

[David G4EBT]

Ye, I guessed you'd have it sorted Mike - I thought it was worth a mention in case anyone went off on a frolic and did their own thing, or wished to use the meters in some other project, as I'm doing. In my case, two separate PP3 batteries will do the trick - one for the project power supply, the other for the meter.

I see that the Sussex thread has now been viewed 8415 times, and had 144 postings with this one! It's go to be top of the pops - way out in front as a home-brew project. (A bit like winning "Pop Idol" Mike, without the dosh and public acclaim to go with it - except of course from forum members

Regards,

David,
G4EBT

[M0XNA Neil]

I'm building the 'Sussex in a suitcase' with bits and pieces I have lying around in the garage. I have built the chassis to sit within an old Maplin black DJ suitcase with room at the side of the chassis for cable storage. Instead of using the panel meters, I am using four cheap Maplin yellow DVMs I have. They will be fixed to the inside of the lid and connected via banana fly leads to the VT panel. By this means I can also use the four DVMs for cathode current balancing in valve audio amps. I will post some photos soon.

Neil.

[David G4EBT]

Good to hear your progress Neil.

re the Maplin yellow perils, yes, they're cheap as chips - sometimes on offer at two for a fiver. I've got them scattered all over the place, bought on impulse - in the car boots, garage, shed etc.

So cheap that they're cheaper than an analogue movement.

Neat idea to use the four set to the desired range and fixed into the lid.

Best of luck with your Sussex!

It will be interesting in due course to see the library of pictures of all the variations on a theme. The PCBs and custom transformer will be a boon to most constructors, I'm sure.

Regards,

David,
G4EBT

[G8UWM-MildMartin]

I now have the PCBs.

They are etched only, and as per Mike's original design (no HT bridge mod.), on 1.6mm fibreglass, undrilled, no resist, no silk screen, etc.

I'm asking £10 including UK post, and promise to pass on the profit from each sale to Mike, regardless of whether all 49 (since I'm keeping one) eventually sell.

[swordholder]

Hi Guys
Attached is a photo of my modified Sussex after fitting Ed's transformer.
Note the addition of the heater voltage selector switch.
The button between the meters is the "Gas" test button mentioned in a previous post.
The printed area of the front panel is 297 x 60mm and can be printed out on standard paper. I used a 2mm clear perspex cover, a lot of firms on E Bay sell A4 size and will cut for no extra cost.
Now that the PCB is available, and Ed's transformer is imminent, it's time to go.

Regards
Mike

[Ed_Dinning]

Hi David, I think it may have been mentioned in an earlier thread. There is a bridge rectifier in the meter, this sorts out the polarity of the supply but is part of the problem if you try to measure the "supply" supply.

Ed

[Ed_Dinning]

Hi Gents, transformers will shortly be ready and I will be sending them out over the next 10 days.
They are wax impregnated and are fitted with stainless brackets for use as feet (drill as you require.
They will be dispatched with full connection details.
I will PM the recipients as they are dispatched.

Ed

[Guitarist28]

Hi Ed
Excellent news and well done

Regards

Rob

[Top Cap]

Although still awaiting the arrival of the PCB, I decided to try and work out how it will interface with the circuit diagram. I decided to give each terminal node an identifier which may (or may not) help me put together my version of the Sussex VT. The info I have put together may be of some use to anyone else building the same and I have put it here:-

PCB with idents:-
http://homepage.ntlworld.com/lez/Sus...%20circuit.JPG

Overall circuit:-
http://homepage.ntlworld.com/lez/Sus...nstruction.JPG

Please note
1) I have not added the bridge rectifier modification yet.

2) The Heater select switch has vacant positions 2 and 3, this is for adding
1.4 and 2V DC supplies later, for directly heated battery valves.

3) I am hoping to be able to switch just one side of the heaters to allow me more switch option positions later.

4) I have yet to decide on D1 and D2 inputs for the Pin selector switches.

Presumably some form of pre-set current limiting would be required here.

There are two R23's on the original board layout and I have re-labelled it as R27. I also suspect that the LED's (except for LED1 on the PCB) are shown the wrong way round?

As the title of one of the drawings suggests, it is work under construction and hopefully you may find some errors that I have missed.

I am going to wait until the tester is built before fitting any ferrite beads etc., I was going to fit chokes until I realised ... the heater current .. doh!
It might be a good idea though to put one in at the Top Cap Grid connection.

The only other change I have made is to fit backstop diodes across the three relay coils, not shown yet across RL1.
Les

[Andymic]

Les,

That is very useful indeed.

Thank you

Andy

[Andymic]

Originally Posted by swordholder

Thanks for that I did realise that, and ED has 3 seperate 6V windings on his transformer

Mike,

Am I correct in assuming this only applies to the dc meters and not the ac?

Andy

[Andymic]

BOM updated... http://spreadsheets.google.com/ccc?k...pfMlE&hl=en_GB

Mike,

Can you give me the part number of the 2p6w switch you used please

Andy

I'm off to bed. It's late !!!

[swordholder]

Andy,
The 3 x 6v windings supply each of the meters (both DC & AC)
Each meter has its own winding.
The switch for the heater is Rapid Pt No 79-0221

Mike

[swordholder]

Les,
Very well done, I dont have any CAD programmes here.
Regarding your connections D1 & D2, I purposely didn't put any rectifier test on the tester.
All the AVO testers appear to run the rectifiers at around 100v.After discussing this with a friend who repairs Hi End audio for a living, he says he has had many current production rectifiers which test perfectly OK on an AVO, yet fail (arc over) when you put 350 - 400v on them. So unless you give them a "good work out" it appears a low voltage test is pretty meaningless.
What are your (and others) thoughts.
It's good others are throwing their ideas into the pot.

Regards

Mike

[Andymic]

Originally Posted by swordholder

The 3 x 6v windings supply each of the meters (both DC & AC)
Each meter has its own winding.
The switch for the heater is Rapid Pt No 79-0221

Mike,

Yes, sorry I had a late one last night. I've taken another look at the diagram and there are indeed 3 separate taps for the meters.
Incidently, only the two DC meters had the warning David mentioned, the AC meter did not (which is why I asked).

Andy

[Guitarist28]

Hi All,
I'm having a Homer Simpson moment here so please excuse my ignorance - what is the value of the pot(?) that is the grid voltage control?

Thanks

Rob

[swordholder]

Rob,
I used a 30K (simply because I had one) but not critical. Rapid do a 50K which should be OK
Mike