The "Sussex" Homebrew Valve Tester.

[Station X]

I've edited the link so it works.

[Mike Brett]

Andy
I built my case from 3 mm aluminium sheet for the top, front and back,and used perforated for the two side panels. Fixed to a simple frame it makes a very neat strong case. The biggest advantage is you can make it to what size and shape you want. I ordered the aluminium already cut to the exact sizes from eBay, this makes it very easy to do a good job.
Mike

[mole42uk]

Originally Posted by ribbonmicsrus

I am looking for the front panel print

I bought some waterslide printer paper off eBay. It's about £1 per A4 sheet, and works really quite well.

The only thing you have to ensure is that you spray a clear lacquer onto the surface after its been through the ink-jet printer and before you put the transfer into water to remove the backing. Otherwise the ink runs. Guess how I know?

Best regards,
Richard

[real2real]

Thanks Graham, Mike and Ricahrd for info, most helpful, I have an aluminium flight case that I will use with the panel fitted on top.
Regards
Andy

[crackle]

Hi
Regarding the “Sussex” valve tester;
I have a question regarding ratings of the high voltage transistors TR1, TR3 and TR5.
These have a voltage rating of 300v. I wanted to use an HT transformer which supplies 300v, which when rectified is slightly over 420v.

Would it be a matter of adding more zener diodes to take the ZD1 to ZD7 chain up to 375v and changing the original TR1 (MPSA92) to a 2SA1625.
Would I need to change TR3 and TR5 (MPSA42) and replace them with BF844.
The BUZ80A FET’s should be OK.
Thanks
Mike

[crackle]

I also have a problem with the bias supply, the voltage will not adjust to 0v.
I have tried various pots and checked the resistance of the pot at the low end and it is 0.5 ohms.
Has any one had this before and got a solution.
Thanks
Mike

[crackle]

Hi
Bias supply problem is sorted, I had left out R24 during some previous tests, the voltage which I saw at minimum setting was in fact the charge on the capacitor. The clue to the omission was, when I went back to try again the bias voltage was at 0v because the charge had decayed.
Has any one got advice to help me re the HV transistors.
Thanks
Mike

[mole42uk]

Mine is nearly running now. Got the oscillator working this morning.....so far, so good!

Most of the parts came from my scrap bin, which is why it looks a little agricultural, but here's some photos:

[mole42uk]

I powered up the tester again today to do some more commissioning. All is well, all voltages as expected, relays open and close as expected.....

But, the 200mV AC meter has died. No illumination, no display.

The meter supply voltage is correct, there's about 5mV on the data terminals.

Has anyone had any similar experience with the ebay DVMs?

I suppose I'll have to contact the vendor for a replacement.

Richard

[MrElectronicman]

I have a several of those meters, mine are ones with a built in range selector, check the solder straps as I have had some problems.

I just put a blob of solder across them, but I have tried adding header pins in an attempt to make the ranges easier to change. If yours are single range I think there are still a couple of straps you might check first.

[Mike Brett]

Hi all
I am in the process of commissioning my Sussex and have come up against my first problem. All was well until I got to test 16. This is apply mains to the valve tester and verify that the grid voltage control can be set to provide 0 to -45 v . My panel meter remained at -00.0 as I advanced the voltage control until the very last couple of turns then the meter read -00.7 but that is as far as it went. I have tried it with a multi-meter but got the same result. Anybody had this problem or could think of what would cause this.
Cheers Mike

[crackle]

I found more than one mistake in my original assembly, mainly complicated by the fact I designed mine around veroboard.
Double check the connections to the MJE350.
I don’t know if this is all taken care of in the pre-made printed circuit board, but have you connected the +ve rail of the bias circuit to the –ve “0 volts” ground.

Mike

[Mike Brett]

Thanks for reply.
Yes the plus ve rail is connected to the 0 volts ground via the circuit board. I have checked the orientation of the MJE350 TR8 which seems correct but the voltages might indicate a fault.
With respect to ground I have 0 volt on the emitter, minus 44 volt on the collector and 0 volt on the base, is this correct or has it gone legs up.
Mike

[Mike Brett]

Another observation. With the Grid Bias 35v wires disconnected from TB-1 10 and 11 all my heater voltages are correct . But if I connect the Bias wires 40 volts appears on the heater pins and altering the heater switch makes no difference, still 40 volts there.
Mike

[Mike Brett]

I really need some help with this guys.
I have been trying to find out how I am getting 40 volts on the heater pins.
As there is 40 volts on the middle pin of TR8 and this is hard wired to C2 and then C4 on relay RL2 when the relay operates there will be 40 volts on the heater pins, why is this.
Can anyone confirm the wiring around RL2 please.
Mike

[mole42uk]

Originally Posted by Mike Brett

Can anyone confirm the wiring around RL2 please.

I did not use the PCB because I have a different relay which is secured to the chassis and wired with discrete cables. I wonder if there's something about connection C4? The 50V supply is there only to operate the relay coil, and doesn't connect to any of the relay changeover contacts at all.

Hope this helps,
Richard

[Mike Brett]

Hi Richard.

That's interesting, only I have 44 volts DC on the relay coil, but also 44 volts DC on pin 14 and 11. Pin 14 is connected to pin AC which is the OV pin, this also has 44 VDC on it.

Mike

[mole42uk]

Hi Mike,

Where is the 44v you measure referenced to?
It is a negative voltage on the relay?

You mentioned earlier that the variable bias wasn't working - have you sorted this out? If the ground of the negative supply is not connected to the ground of the 300v supply, you might find there's -44 on the GND side of the 300v.

HTH
Richard

[mole42uk]

I have started compiling a Switch Setting Table for the Sussex. I have attached a zip file.

Has anyone any ideas for improvement? Please feel free to comment or edit the file.....

Richard

[Mike Brett]

Richard
That looks a great piece of work, will make life simpler if and when I get my Sussex working.
Mike