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Old 5th Apr 2013, 6:06 pm   #801
Top Cap
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Default Re: The "Sussex" Homebrew Valve Tester.

Nicely spotted PCB error Mike, it might be the answer to a long standing problem with my Sussex when, after testing and setting the Function switch to a leakage position, I suddenly had a leakage warning that slowly decayed. There was me looking all around the negative supply for an answer not realising the problem may have been due to HT still being present. I will definitely do the track cut modification later and maybe that errant leakage problem will stay away. I attach an Xray view of the PCB showing what I think is the required track cuts, there is also a rather poor archive view of the PCB Track in that corner. Les
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Old 5th Apr 2013, 6:18 pm   #802
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Default Re: The "Sussex" Homebrew Valve Tester.

Yes I was getting that Leak light staying on decaying with the HT. I actually liked that visually as it felt comforting for some reason.

Attached is a pic of my modified PCB.
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Old 5th Apr 2013, 6:30 pm   #803
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Default Re: The "Sussex" Homebrew Valve Tester.

PS TopCap - I do agree with your track cut instructions.

The only problem I am having now is with my gM measurement. I have attached a scope trace as I can see some wobble on the waveform but I don't have enough experience to know if it is significant.
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Old 5th Apr 2013, 8:39 pm   #804
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Mike, did you set the grid drive to 100mV using an rms voltmeter? I found my Sussex gave sensible readings. My test valve that I keep just for that purpose is an EL86, the expected figures are almost identical to that obtained on the meters. Although it does not really prove 100% accuracy, I was happy with that and subsequent readings with other valves are, shall we say (tongue in cheek), realistic enough to be believed. I find the Sussex most useful for finding shorts/leaks and determining differences for matching purposes.
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Old 6th Apr 2013, 3:50 am   #805
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Default Re: The "Sussex" Homebrew Valve Tester.

A further thought about the discrepancy, maybe it's not a bad idea to leave the feed to D3-5, R2 and the LED permanently in circuit as a bleeder and just move R1 to share the switched side with the MOSFETs?
TR1's B-C junction should withstand it.
Also, wouldn't it be better to have RL1's contacts in series rather than parallel (2 track cuts and 1 wire link)?
Shame Mike Rowe's not still around, but could anyone else analyse & comment, please?
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Old 6th Apr 2013, 11:09 am   #806
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
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Hi Mike, did you set the grid drive to 100mV using an rms voltmeter?
TopCap, I have set my grid drive to 100mV (measured on the grid socket) although it wasn't with a true RMS meter but I am not sure if this will give enough error to be significant. The meter that I have is a Tenma 72-7740 (which is about £40 DVM from Rapid). It claims to have 1% accuracy on the mV range but I am beginning to have doubts about that as if I hold the meter in my hand whilst measuring low voltage signals the value increases e.g. measure 10mV on the bench, then 22mV in the hand. The meter has been dropped more than once I have to say. . . so I am wondering if I can rely on this.

Right now I am reconnecting my valve bases back up and will try out some other valves especially ECC83 as it will be interesting to see the results on a lower gm valve.

Will post back results as soon as

Thanks to everyone for reading and providing support on this fantastic forum.
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Old 6th Apr 2013, 5:35 pm   #807
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Default Re: The "Sussex" Homebrew Valve Tester.

This is aimed mostly at TC.
On the relay daughter board do we have to run a wire between C4 and C2 and also between C4 and B2, as there is no tracking on my PCB.
Cheers Mike
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Old 6th Apr 2013, 6:40 pm   #808
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi,
Long time since I started this but...thanks for the PCB... thought you might like to see progress...

http://m1kta-qrp.blogspot.co.uk/2013/04/sussex-valve-tester-construction-so-far.html


I had to 'adjust' the polarity of a few things as the layout was not quite right but seems to be fine so far. I used 2N3906 instead of BC307 for TR6/TR7.

C4/5/6 were very tight fit but I managed it.


72

Dom
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Old 6th Apr 2013, 7:02 pm   #809
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Mike, it has been a long time since I built mine and I may have to take my Sussex apart to confirm, but Yes I believe these links were added later. They may have been part of the change to prevent the -45v supply being shorted by a faulty valve under test. It looks as though I also broke the track that connects pin 14 of RL2 to the solder pad/pin C4. A separate wire then links pin 14 of RL2 to 0V obtained at the mother board pin AC. So the Green wires on my sketch of that board are indeed added links, an extra one also added for the Fan supply which you may/may not be using. For love nor money can I see what my note concerning breaking the track under R29 means, oh how the memory fades ever quicker as years roll on. Les
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Old 6th Apr 2013, 7:56 pm   #810
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Default Re: The "Sussex" Homebrew Valve Tester.

Many thanks TC for the confirmation on the daughter board wiring.
Mike
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Old 8th Apr 2013, 8:44 am   #811
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
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For love nor money can I see what my note concerning breaking the track under R29 means, oh how the memory fades ever quicker as years roll on. Les
See post #757 and #758 - I had the exact same question.
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Old 8th Apr 2013, 8:58 am   #812
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Default Re: The "Sussex" Homebrew Valve Tester.

Yes Mike I had seen that page earlier but had forgotten about the question you raised, so many pages to read through.
Mike
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Old 9th Apr 2013, 12:40 am   #813
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Default Re: The "Sussex" Homebrew Valve Tester.

Post 409 shows what happened to R29, it certainly was the heater continuity modification.
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Old 9th Apr 2013, 8:55 am   #814
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Default Re: The "Sussex" Homebrew Valve Tester.

What a fantastic project this is, very occasionaly I have looked in to see how things were going and might be tempted to try collecting components for this project whilst I can.

I seem to remember that someone suggested or perhaps had used cheap DVM instruments to display the various voltages. These were instruments that had been partialy disected to use just the displays.

Does anyone know of this particular posting because my memory loss has hampered me greatly in trying to find out more about these "disected instruments" so any help would be welcomed.

I have searched but ended without a trace.

Many Thanks
Tony.
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Old 12th Apr 2013, 10:27 am   #815
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi all
On post 124 there is a picture of relay RL3 that seems to have the pins marked wrong. Pins A1 and A2 seem correct but pins 12- 22, 11-21, and 14- 24 look to be reversed. This is important as the minus and plus pins to the DVM are the wrong way around. I have the plus to pin 11 and the minus to pin 21, is this correct.
Mike
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Old 12th Apr 2013, 11:59 am   #816
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Default Re: The "Sussex" Homebrew Valve Tester.

Having thought about this a bit more I suppose it does not really matter if the relay pins are reversed, it is just a switch after all. As long as the wires go to the correct locations I should be alright, yes?.
Mike
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Old 12th Apr 2013, 7:06 pm   #817
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
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I seem to remember that someone suggested or perhaps had used cheap DVM instruments to display the various voltages. These were instruments that had been partially dissected to use just the displays.
Hi Tony,

I recall that posts #687, #708 and #730 dealt with cheaper meters, but I don't recall anything about "dissected instruments."

I brought up some points questioning the accuracy of the DVMs in posts #663 and #664, but I believe that I was probably getting pick-up from long, unscreened leads which messed up my measurements. I recall that this was all put to bed eventually by more rigorous measurements.

Although "Georgio" seems not to stock the DVMs any more, they are available if you nose around. I bought a couple just recently, as the 200mV AC ones are a little delicate and easy to ruin.

I hope this is what you were looking for.

Regards, Colin.
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Old 13th Apr 2013, 4:17 pm   #818
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Default Re: The "Sussex" Homebrew Valve Tester.

Thanks Colin for the responce, much appreciated.

Sadly I suffer with short term memory loss and for the life of me cannot remember where I saw these disected DVM's I thought it a smart solution and easy to replicate in my location. The Norwegian customs and exise always seem to stiff us that order parts from abroad and the cheap "disected" dvms were a good idea.

I have a vague idea that the instruments might have been intended for a capacitor reforming project but will have to keep searching when I get time.

Again thanks Colin for the posting numbers

Regards
Tony
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Old 13th Apr 2013, 4:42 pm   #819
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
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Sadly I suffer with short term memory loss and for the life of me cannot remember where I saw these dissected DVM's
Ha! Tell me about it. At my age (66+) I sometimes have difficulty in remembering where I put a cup of tea down.
Quote:
Originally Posted by Anthony Thomas View Post
I have a vague idea that the instruments might have been intended for a capacitor reforming project but will have to keep searching when I get time.
Hi Tony,

No problem. I have now found out where I bought my DVMs from; it was "Daifengsu" and the 200mV AC meter is currently on offer at £5.39 UK Sterling. They get delivered from Hong Kong in small cardboard boxes (13 x 8 x 7.5mm) and the UK customs seem to ignore them. They do take a couple of weeks or so to arrive, however. As far as I can see, there is no declaration of the value of the enclosed items, so you might get lucky, too.

I'm sorry that I can't recall any capacitor reforming project which used anything like the DVMs you refer to. Have you tried doing a "search" on the forum? I find it works very well for things that I thought I had seen somewhere, but can't remember quite where.....

Regards, Colin.
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Old 13th Apr 2013, 5:33 pm   #820
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi all
I am just about to order my meters from Asia Engineering and I intend to install an extra meter to show the heater voltage. Could anyone else that has done this modification please give me an idea of the DC voltage I should buy.
Many thanks Mike
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