The "Sussex" Homebrew Valve Tester.

[hughtmccullough]

I am thinking of making a valve tester based on this design and I have a couple of questions:

Does anyone know if there are any PCBs still available? I can always get some made but I thought I would ask first.

I have been studying the design and I am wondering why RL1 is needed. When the function switch is in any position other then "Test", the Va supply and G2 supply outputs are not connected to anything. So, all the relay does is remove the input to the power supply. In the "Test" position, two things happen: the relay RL1 closes and the Va and G2 supplies are connected to their respective bases. Yet, I think some people reported odd results if the relay becomes bypassed. Is this just belt and braces or am I missing something (very possible)? How would replacing RL1 with a link cause problems?

[jackrae]

My ha'-pennies worth :
Because up to 350v DC is being switched, it is a simple safety device on two counts A) it aleviates the need for a selector switch rated for at least 350v switching (both on and off-load) and B) it provides isolation of the selector switch wiring and contacts (plus dabbling fingers) from the stored energy of the smoothing capacitors.

[hughtmccullough]

Jack,
Thanks. Yes that makes perfect sense and it does also emphasise the need to follow precisely the operating procedure. I'll continue reading a bit before I pick up the soldering iron!

[vidjoman]

The only mod I did with mine was to fit a set of 12 volt relays with contacts rated at 10 amps to supply the heater voltages as getting a suitable high current switch was difficult, so I used a standard switch rated at about 1 amp and that switched the relays. They were for use in a car and only about the size of an OXO cube. Stuck to the front panel with double sided adhesive foam tape. I fitted a small extra power supply to feed them.

[Diabolical Artificer]

I recently built a homebrew valve tester and faced similar issues switching HV etc. My first tester I think switched HV anode & g2 by switching the AC supply to the power supplys. The last iteration I went for switching/connecting HT by switching the grounds on/off, however I experienced odd issues which I couldn't resolve.

In some of my amps I've used Omron 3 x DPST relays to shunt out a resistor as in a soft start circuit. I parallel all three sw's, so far I've had no failures, this is with HT of 400v & up.

Andy.

[Urbanus]

Hi All,
Just posting a quick note to wish everyone still watching this thread a very Merry Christmas and a Happy New Year.
I discovered the "Sussex" whilst researching information for an old AVO valve tester I was considering buying but which had the valve panel missing. After reading through all 87 pages of the thread I decided my time might be better spent building the Sussex rather than faffing about with the AVO (although I might still buy it if I can get it down to a reasonable price!)
After contacting Martin and Ed I now have the starting materials for my job bin - a set of PCB's and a Transformer so now the search for the remaining components begins.

All the best
David