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Old 20th Jan 2017, 12:46 pm   #1361
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Default Re: The "Sussex" Homebrew Valve Tester.

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Originally Posted by Chicoull View Post
Further to my last post...when my template is fitted to the face panel, I will be able to start installing switches, valve holders etc. Looking at the wiring between the pin switches and valve holders, it appears that the nine cables are screened - is that correct? if so, will standard microphone wire do, or more heavy duty satellite cable? The screens are all linked together and output to "a" - is that the board earth connection?
I can only describe what happened with my unit. I originally had it wired with ordinary coloured wire but had problems with some valves oscillating.
I re-wired with single screened microphone wire but it had little effect. The use of Ferrite beads and loop wiring seems to do the trick better according to others. Point 'a' is indeed the board Ground. With so many variants of actual build it is difficult to suggest any one particular thing but screened leads would usually be the thing to use first to reduce coupling of signals leading to oscillation.
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Old 20th Jan 2017, 2:22 pm   #1362
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Vidjoman,

The link to the user guide is in post 1333 - a cut down version of that produced in 2014.
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Old 20th Jan 2017, 4:30 pm   #1363
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Default Re: The "Sussex" Homebrew Valve Tester.

The very first post is where you get the official manual as stated:-

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

This manual supersedes the documents below (however the links remain for reference).
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Old 20th Jan 2017, 4:36 pm   #1364
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Default Re: The "Sussex" Homebrew Valve Tester.

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Originally Posted by Chicoull View Post
The link to the user guide is in post 1333 - a cut down version of that produced in 2014.
As I had the original I didn't look at the cut down version.

I have fitted in my version a switch to link the heater- to cathode (earth) for those valves that need it, but have not included a level test as I find mine is stable. I have checked the level - via the grid socket - each time I've used it and it's only once varied (by 1mv) since I completed the tester.
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Old 20th Jan 2017, 4:37 pm   #1365
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Default Re: The "Sussex" Homebrew Valve Tester.

None of my valveholder leads are screened and I have only put one ferrite bead on each loop. Didn't find I wanted to fit a bead to every pin of every valveholder! I have only three valveholders in my Sussex though I do have a grid stopper fitted to the Octal socket.
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Old 5th Feb 2017, 3:31 pm   #1366
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi All, I have been doing functionals - Powered the unit up and it pretty much worked as advertised!!! The only thing I failed to get was LED 1 lit when required. I thought I may have wired it up wrong, but when checking the PCB tracks, it appears that the circuit flows from the Cathode of D5, thru the LED, then via R2 to Ground. On the Circuit, R2 appears before the LED - acting as a dropper? Should these two be reversed on the PCB? or would you expect the LED to light irrespective of its position in relation to R2?

Regards, Charles.
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Old 5th Feb 2017, 3:40 pm   #1367
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Default Re: The "Sussex" Homebrew Valve Tester.

I don't know this design, but if R2 is simply the series resistor for LED1 (and there is nothing else connected to the point between them) then it doesn't matter if the circuit is +ve supply - R2 - LED1 - Ground or +ve supply - LED1 - R2 - Ground. The current will be the same in each case. It's just a simple series circuit (albeit one with a non-linear device).
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Old 5th Feb 2017, 3:53 pm   #1368
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Default Re: The "Sussex" Homebrew Valve Tester.

So it does not matter that the voltage would be well in excess of the rated 5V for the LED, it is only the current that matters?
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Old 5th Feb 2017, 3:59 pm   #1369
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Default Re: The "Sussex" Homebrew Valve Tester.

When current passes through a resistor a voltage is developed across it. The is commonly known as "the volt drop". This means the LED will see less than the voltage applied to the resistor and LED in series.

Have you taken any voltage readings?
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Old 5th Feb 2017, 4:06 pm   #1370
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Default Re: The "Sussex" Homebrew Valve Tester.

No readings, I had to remove the PCB from the panel to check the LED was wired in correctly - it was then that I noted the PCB tracking differed from the Circuit Diagram. The PCB layout is as the attached pic - the Circuit Diagram has the LED and R2 reversed.
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Old 5th Feb 2017, 4:10 pm   #1371
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Default Re: The "Sussex" Homebrew Valve Tester.

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No readings..
Wot?

No 300V supply? Nothing on the diodes? Nothing on the transistor?
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Old 5th Feb 2017, 4:18 pm   #1372
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Default Re: The "Sussex" Homebrew Valve Tester.

Sorry - you misunderstand me. I have no readings at the LED. The voltage at the fuse was in excess of 300V DC. As all was well during the rest of the installation checks, only the LED not lit when required, I assumed I had connected the LED in reverse. Ripped the PCB out to swap the LED connections and noted the difference in the circuit layout. The LED was probably reversed because I fitted it in relation to how I saw R2 on the Circuit Diagram - there were no Anode/Cathode markings on the PCB.
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Old 5th Feb 2017, 4:21 pm   #1373
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Default Re: The "Sussex" Homebrew Valve Tester.

Not sure what D3 -D5 are doing, but I seem to remember on TV Circuits, diodes in series caused an increase in voltage - if so, the voltage at the LED would be well in excess of 300V.
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Old 5th Feb 2017, 4:22 pm   #1374
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Default Re: The "Sussex" Homebrew Valve Tester.

In the original circuit, would the resistor R2 drop that voltage down to the LED operating voltage of 5V?
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Old 5th Feb 2017, 4:36 pm   #1375
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Default Re: The "Sussex" Homebrew Valve Tester.

Yes. If 300V is connected across a 120k resistor the current will be limited to 2.5mA.

So long as the LED and resistor are in series it doen't matter which order they're in.
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Old 5th Feb 2017, 4:43 pm   #1376
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Default Re: The "Sussex" Homebrew Valve Tester.

If the positions of the LED and resistor are swopped over on the PCB when compared to the circuit diagram, then no voltage across the LED suggests it's short circuit.

Remove it and you'll probably see 300V on a meter, but that's not what a diode would see.
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Old 5th Feb 2017, 4:44 pm   #1377
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Default Re: The "Sussex" Homebrew Valve Tester.

OK, will refit LED as per PCB layout - reconnect to panel and do functionals. Will take some time to reconnect everything and while I am doing that, I will shorten some of the wiring. So back with results sometime tomorrow.

Thanks - Charles.
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Old 6th Feb 2017, 7:28 am   #1378
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Default Re: The "Sussex" Homebrew Valve Tester.

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there were no Anode/Cathode markings on the PCB.
There is one flat side on the LED symbol on the PCB which denotes the Cathode as per standards used in PCB markings of LEDs, the other side is rounded denoting the Anode.
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Old 6th Feb 2017, 7:33 am   #1379
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Default Re: The "Sussex" Homebrew Valve Tester.

If your LED is an older type it will not light up much at all at this low current, modern LEDs will shine a lot more - there are even low current LEDs which shine a lot more at lower currents than standard types do as the standard types are mostly made to shine as much as possible whereas the low current types are made to shine at low currents.

You'll have to make sure that the 120k resistor can dissipate some 2W as it will either be destroyed or de-solder itself from the PCB if it gets too hot.
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Old 6th Feb 2017, 3:52 pm   #1380
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Again, refitted LED as per PCB layout - rewired panel and a further test gave LED1 lit when required. full test carried out on an ECC82 and all seemed to go well. The gm reading was higher than expected 3.7 instead of 2.2 approx. - don't know if too high is possible? Checked two different battery valves - 1R5 and 1T4 - both passed, again with gm readings higher than expected.

My apologies to Dekatron - my comment regarding Anode/Cathode markings was not a slight on the PCB - I was not aware of the current labelling of LEDs. He was quite correct - the panel was labelled correctly and if I had known about the Standard markings, I would have got the position right at the first attempt.

My thanks to all contributors to this forum - it would not have been possible to get this far without you.

Regards, Charles
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