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Old 13th Dec 2011, 7:03 pm   #621
Dekatron
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Default Re: The "Sussex" Homebrew Valve Tester.

Andy,

Have you thought about the short circuit current which will be fed through the tracks on the PCB for Anode, Screen and Heater voltages? To me the tracks look a bit thin and since you are using a dual layer PCB it might be hard to replace the rotary switches or other components or repair the tracks in case of a failure.

I know that the Anode and Screen voltages are short circuit protected, but if that fails the full voltage/current might be fed through the circuit. The heater voltages do not have the same protection and a fuse might blow slower than a thin track.

Making the tracks wider will not only protect them from being destroyed but it will also decrease the voltage drop if they are long, like on the switch PCB.

Another way of connecting rotary switches to a PCB is to make the PCB simpler with just wide tracks with holes for wires connecting the switch to the PCB. The rotary switch can then be mounted at the front panel and the PCB right behind them. Or the rotary switches can be mounted at the back of the PCB , with shafts through the PCB and screwed to the PCB. This way just letting the shafts through the front panel with a few screws with distances securing the PCB to the front. Both of these ways of mounting them will make it easier to repair or exchange them if it will be necessary. De-soldering Switches from a PCB is harder than soldering wires to the switches or PCB.
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Old 13th Dec 2011, 7:13 pm   #622
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Default Re: The "Sussex" Homebrew Valve Tester.

Can anybody identify the maximum current available at the anode, screen and heater using the standard transformer?
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Old 13th Dec 2011, 7:20 pm   #623
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Default Re: The "Sussex" Homebrew Valve Tester.

Found the specs that Ed worked to. They are;
0-250V at 120mA
0-30v at 20mA
0-6v at 50mA (times 3)
0-4-5-6.3 (@3A)-12.6v at 1A

I'll check the required track thickneses

Andy
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Old 13th Dec 2011, 7:25 pm   #624
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Default Re: The "Sussex" Homebrew Valve Tester.

Ok
Based on 1oz/ft board.....
The 3A taps net to be a minimum of 1.37mm
The 1A tap needs to be 0.781mm
I don't need to worry about the others are the thinest track is already 0.8mm

Andy
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Old 13th Dec 2011, 8:12 pm   #625
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Gents, how about getting the pcb's made with 3oz copper, not much extra cost.
It would also be possible to fuse the transformer outputs as the s/c current will be much higher than the rated figures given above.

Ed
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Old 13th Dec 2011, 8:16 pm   #626
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Default Re: The "Sussex" Homebrew Valve Tester.

3oz copper brings the trace width for 3A down to 0.456mm
2oz copper makes the trace width for 3A 0.68mm

Sounds like a plan........
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Old 13th Dec 2011, 8:32 pm   #627
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Gents, even at 3oz, keep the tracks fat for low drops and robustness under s/c conditions. I'm from the "minimum etch" school.

Ed
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Old 13th Dec 2011, 9:02 pm   #628
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Default Re: The "Sussex" Homebrew Valve Tester.

Ed
I'll 'fatten up' all the tracks.

Quick question; Is the general consensus to include the mods that Top Cap made in order to add the additional heater voltages and the diode test facility?

The layouts I've done so far are to Les' original schematic.

Andy
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Old 13th Dec 2011, 9:03 pm   #629
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Default Re: The "Sussex" Homebrew Valve Tester.

Oops, I meant Mke's original schematic
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Old 14th Dec 2011, 1:42 am   #630
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Default Re: The "Sussex" Homebrew Valve Tester.

I'd go for all the additions and options if possible, on the grounds that it's a lot easier to omit them when building than to add them.

Then there's the huge difference in tooling costs between a top-quality double-sided PCB, drilled, with PTH (plated through holes), solder resist and silk-screening, let alone production cost, compared with a no-frills, etch-only undrilled (or drilled) run to consider, even if the constructor does have to mess around with wire links all over the place for single-sided and even if it needs to be bigger.
And it's much harder to etch at home and poke an iron under components to solder the top side if no PTH.
I suppose it could be laid out to allow those wretched old track pins that always seemed to have dry joints to avoid PTH.
But on balance I'd suggest trying to make them single-sided.

Best regards,
Martin.
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Old 14th Dec 2011, 8:49 am   #631
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Default Re: The "Sussex" Homebrew Valve Tester.

I agree with martin (G8UWM-MildMartin) regarding the use of single-side PCB, it is much easier to solder and repair those compared to double-sided.

If you try to keep all links as short as the cut pins from components those pins can be used and the spill will be less.

Also making the tracks as wide as possible without getting to close to each other will also save etching time as Ed suggested earlier. Another benefit from wider tracks is that they will work as heat reliefs for components decreasing the risk of dry-joints appearing after some time.
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Old 14th Dec 2011, 9:55 am   #632
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Andy,

I speak from many years experience in designing PCBs for high voltage use that they do appear to be a little 'close' in some parts.

FYI international standards recommend a minimum spacing of 1.25mm for 300V DC, some say more.

Just my 2p worth...

Adrian.
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Old 17th Dec 2011, 5:18 pm   #633
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Default Re: The "Sussex" Homebrew Valve Tester.

My first post here, as I was pointed to this superb project, and will definitely be building one.

Are the transformers still available, (aimed presumably at Ed), and PCBs?

As this is my 1st post it might seem a bit of a 'begging letter', but this will be an invaluable addition to my workshop.
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Old 17th Dec 2011, 10:09 pm   #634
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi, You are in luck, I've just wound 2 Sussex transformers. One has been sold but the other is still available. You should be able to PM me now, or you can send me an e-mail and I'll get your address etc and get one off to you. A nice Xmas project.

Best regards, Ed
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Old 18th Dec 2011, 1:06 am   #635
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Default Re: The "Sussex" Homebrew Valve Tester.

Thanks Ed - I'll definitely have it. Shame I don't still live in the NE - I could just have picked it up;

I'll try the PM thing...
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Old 18th Dec 2011, 11:32 am   #636
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Default Re: The "Sussex" Homebrew Valve Tester.

Amgardelec, you have a PM.

Ed
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Old 18th Dec 2011, 1:16 pm   #637
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Default Re: The "Sussex" Homebrew Valve Tester.

Thanks Ed, you have a reply.
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Old 23rd Dec 2011, 9:34 am   #638
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Default Re: The "Sussex" Homebrew Valve Tester.

Great project!
Thank you all for creating it. IŽd be interested in joining the project.
Can someone let me know about where to get all the parts?
Have anyones built a prototype or the like working OK?
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Old 26th Dec 2011, 10:55 am   #639
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Willie, I've made about 36 transformers, and I don't think they are all used as paperweights, so there must be a few working testers out there.
Possibly some of the members are shy about their achievements or they are just busy testing valves. It is an extremely useful project, with plenty of support here, so go for it.


Ed
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Old 27th Dec 2011, 6:06 pm   #640
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Default Re: The "Sussex" Homebrew Valve Tester.

Thanks for your answer Ed, I appreciate it.

I'd like to be sure I can get all the parts nowadays because I would have to spend money and if any part is not avalaible I would have to wait or let it go.

I just noticed this is a great forum with great support.
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