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Old 25th Oct 2019, 5:03 pm   #1521
G8UWM-MildMartin
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Default Re: The "Sussex" Homebrew Valve Tester.

PCBs arrived from China this morning. I only ordered 10 sets this time.
They work out at £7.80 a set, plus postage at 70p UK, £1.60 Europe, £2.30 rest of world.
PMs sent.
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Old 3rd Nov 2019, 7:18 pm   #1522
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Default Re: The "Sussex" Homebrew Valve Tester.

I ordered the parts for this tester when Mike had published details. For various reasons never got round to finishing it.
Problem is that the relays were only two, now three. I have been unsuccessful in locating the original part as I believe now discontinued by Finder the 41 series low profile.
Can anyone tell me if the 40.52.9.048 version will be OK, coil resistance is bit lower etc.
Or does someone know source of supply of the correct part.
Andy
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Old 3rd Nov 2019, 8:29 pm   #1523
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Default Re: The "Sussex" Homebrew Valve Tester.

Correction, it has always had three relays, as parts were ordered after the "gas" test modification, I must have lost one!!!!

Last edited by ribbonmicsrus; 3rd Nov 2019 at 8:33 pm. Reason: spelling
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Old 3rd Nov 2019, 11:36 pm   #1524
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi,

Is the BOM that is posted in the first post up to date with the PCB?
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Old 4th Nov 2019, 1:15 am   #1525
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Default Re: The "Sussex" Homebrew Valve Tester.

The latest BOM for main pcb with LR8 fitted is linked on post #1498, although it shows the extra components for LR8 circuitry under daughter board.

Andy
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Old 9th Nov 2019, 8:44 pm   #1526
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Default Re: The "Sussex" Homebrew Valve Tester.

Have received the latest PCB from Martin, super quality, and nearly finished assembly. Testing in stages, with a 9v supply the ocillator worked a treat with BC307Bs. Next thing is to power up the 48 v supply and check that is OK, then the HT supply.

Having bit of difficulty associating some of the terminals with the original wiring diagram, partly because most of the external boards are on the main PCB now.

Going to add a heater voltage meter, I was hoping to squeeze some wire in existing bobbin but no room as filled to laminations so another transformer.

Andy
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Old 9th Nov 2019, 9:56 pm   #1527
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Andy, why not use an analogue meter ?

I can do an extra meter supply on the transformers if requested when ordered.

Ed
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Old 10th Nov 2019, 12:57 am   #1528
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Ed

Yes, could do, but have a few of the digital meters, all matching as originals.

I was aware you could add an extra winding, but bought this transformer from you a few years ago before the heater discussions arose. I have a small 6VA transformer that will do the job nicely.

Andy
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Old 11th Nov 2019, 1:42 pm   #1529
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Default Re: The "Sussex" Homebrew Valve Tester.

Just noticed on new board, that "Jreg" marking is incorrect. The 2V o/p is 1.4V and vice versa. Of course you can reverse this by swapping over the resistors setting the o/p voltages to the other regulator.
And yes, did check I had fitted parts as per circuit diagram.

Also onboard LR8 regulator works well.
Andy
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Old 12th Nov 2019, 9:29 pm   #1530
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Default Re: The "Sussex" Homebrew Valve Tester.

Thanks for finding that error! I don't think anyone has approached me on that before (unless I forgot about it of course).

I can recommend you to swap the resistors to keep the text intact on the circuit board instead of swapping the wires in the contact.

I'll update the schematic (and perhaps make a better one) and also the circuit board when I have some time, can't promise anything on when that will be done though - time is one of the things I never have enough of in life it seems.

/Martin
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Old 13th Nov 2019, 3:24 pm   #1531
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Default Re: The "Sussex" Homebrew Valve Tester.

Martin

Found another small problem in that the 250mA QB fuse blows when RL1 energises. It is due to inrush current on C17, the original circuit with the current mirror did not have any decoupling on that side. Removing C17 avoids the fuse blowing. I have not noticed any instability with U1, the LR8 regulator when just relying on just the 220nF.

Andy
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Old 13th Nov 2019, 7:10 pm   #1532
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Default Re: The "Sussex" Homebrew Valve Tester.

That seems strange to me - is there any chance that you can hook up a scope to see what the current pulse looks like and measure it. Having a quick look at some fast blow 250mA fuses and their ratings I can't see how it can blow as they should withstand the current from the 4.7uF+220nF capacitors when they charge with a wide margin.

If anyone else has seen that behavior it would be good if you can leave a comment here. The small 4.7uF/400V capacitor is necessary so the LR8 doesn't start to oscillate, 220nF is to low for that.

How much of the rest of the circuit after the fuse was soldered?

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Old 13th Nov 2019, 9:19 pm   #1533
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Default Re: The "Sussex" Homebrew Valve Tester.

Yes, that's what I thought, have tried another capacitor just in case. The fuses were from RS, supplied by Taiwan company so hopefully OK. Have TR2 and TR4 wired correctly with the anode/screen switches in circuit, no other loads downstream. Circuit is working correctly as 0-300V selectable in correct sequence. Will try and scope it tomorrow if have time.

Andy
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Old 13th Nov 2019, 10:07 pm   #1534
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Default Re: The "Sussex" Homebrew Valve Tester.

I have tried a 1uF and there is no stress on the fuse, and no instability.
As I am only running short wires to anode/screen switches for test purposes have not fitted 22uf caps yet.

Andy
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Old 14th Nov 2019, 2:52 pm   #1535
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Default Re: The "Sussex" Homebrew Valve Tester.

Do you have another 4.7uF/400V to test with?

/Martin
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Old 14th Nov 2019, 4:28 pm   #1536
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Default Re: The "Sussex" Homebrew Valve Tester.

Yes Martin
As mentioned earlier did try with another, same result, possibly a duff batch, measures OK on my LCR bridge but can't test it polarised with a DC source easily.

I do have a large 4.7uf 500v polyester somewhere, if can find that will try.

Can't finish it all yet as other half told me you can have your case at Christmas, not before, although the Electrode and Function switches are assembled as well, those small switch PCBs are great.

Andy
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Old 14th Nov 2019, 5:01 pm   #1537
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Default Re: The "Sussex" Homebrew Valve Tester.

Sorry, missed that you had already tried a second one.

I re-read the thread snd saw that you wrote QB fuse, is that something quicker than Fast Blow? Iím only used to three types in Swedish, so I donít know the proper English words for them - but they are: Slow, Normal and Fast. Is QB faster than Fast?

What happens if you try a Normal fuse?

/Martin
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Old 14th Nov 2019, 6:41 pm   #1538
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Default Re: The "Sussex" Homebrew Valve Tester.

Martin

I think it is a standard fuse, my terminology was QB. The ones I acquired from RS were either anti surge (T) or normal (F), the type I am using. These were the only types listed.

I assume the LR8 regulator would be OK with around 45uF decoupling on its output when I have finished building or would you say not necessary or something like 1-4.7uF instead on each switch. I would imagine only effect would be to put the device into current limit for a short period.

Andy
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Old 14th Nov 2019, 7:16 pm   #1539
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Default Re: The "Sussex" Homebrew Valve Tester.

The datasheet says a minimum of 1uF on the output of the LR8 and a minimum current draw of 500uA on the output.

The input capacitance value is from my own experience with the LR8, you can use higher values but with the reservoir capacitor after the rectifier that is more than enough. The minimum current draw requirement is met by the voltage divider chain for the LR8 with the addition of the two switches with their resistor chains (close to 1mA).

The output capacitance of the LR8 doesn't need to be big, I've used anything from the recommended 1uF up to 10uF with perfectly good results in circuits like this where you draw very little current from the LR8.

You will probably only see oscillations if the valve oscillates or at turn on/off situations.
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Old 15th Nov 2019, 11:01 am   #1540
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Default Re: The "Sussex" Homebrew Valve Tester.

Thanks to ribbonmicsrus I have just obtained a version 9 board (ver4 + LR8 bd) and am building my own Sussex.
However I intend somewhat modifying it, the principle change being to not use a single transformer but use what is in the junk box, viz a Gardner oil filled transformer for HT and the meter supplies (3X6.3V windings), a second transformer for the 35V, grid supply and a DC SMPSU for the heaters.

I see from the schematic that the heater supply is floating, except for directly heated valves when the heater is linked to Cathode, which is held at 0V.
Is there any reason why the heater supply cannot also be referenced to 0V rather than floating?

Peter
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