The "Sussex" Homebrew Valve Tester.

[Ed_Dinning]

Hi Tony, The transformer is designed with some compensation so its open circuit voltage is above nominal, falling to the correct value on load. This will also depend on mains input voltage.
If you are looking to compensate for switch drop without using an external supply, simply use the next voltage up and connect a low value high current variable resistor in series with the common lead of the heater supply. It should then be possible to set the heater voltage very accurately with an AC voltmeter.
If you are going for this accuracy I suggest you monitor it during the testing as in some areas the mains voltage will vary with time quite a bit.

Ed

[Tony Jaques]

Hello Ed,
Thank you for that, but I did not use your transformer.
However my 4 and 5 Volt winding is my own addition to a transformer that I was given, (see piccy on an earlier post). I did aim for 5.3V without considering the switches at the time. If I have reason to break it all down for some reason I will add a couple more turns to the winding, but it is not important enough in practice to take it all apart to do just that.

A note about the GZ32:
I was mislead by its indirect heater. What I missed is that the cathode is internally strapped to the heater and not brought out to its own pin.
So my earlier post on the subject is not just limited to obviously directly heated valves!

Tony...

[George G4EUF]

Originally Posted by G8UWM-MildMartin

I still have (28) PCBs for sale at cost (8.12 GBP).
Plus, maybe, the cost of a padded envelope, depending on whether any suitable used ones are being thrown away at work, plus the ever-increasing Royal Mail postage cost, minus the discount from using the franking machine at work, plus any applicable curency transfer or exchange fees.

Hello Martin,
Do you still have any PCBs available for the valve tester?
Regards.
George G4EUF.

[gmonno64]

Hi, if PCB were available I'd like to have one too.

Thanks and best regards

[George G4EUF]

Hello all,
Has anyone as yet produced a PCB for the daughter board, I no longer have the facilities for producing PCBs?
George.

[George G4EUF]

Hello to Tony Jaques,
Tony, like you I have considered using decade switches instead of the wafer switches, I have not as yet started construction so I am interested as to how you have got on with them for your project?
Regards.
George.

[George G4EUF]

Hello Tony,
I have now answered my own question by looking back through your previous threads having spent an hour or so looking at all the relevant threads with regard to the "Sussex", as a result there is no need for you to reply. Many thanks.
George.

[George G4EUF]

So far, so good.

[George G4EUF]

Les,
Hope you don't mind my asking? however, where did you get hold of the rather nice numbered knobs for your version of the "Sussex"
George.

[Top Cap]

Hi George, the knobs and accessories were Sifam except for the figure dial which are an RS item. I have checked RS for availability as I did not think the knobs would be available now, Sifam having moved production to China and may have stopped producing these items. However they are still available from RS as a quantity of 10, well it gives you some spares
The 15mm collet knob is RS 225-704 made for 1/4" switch spindles and priced at £1.40 each. The Sifam Part is S150 250-BLK.
The cap for these, to cover the fixing nut, is RS 225-899 and priced at 11p each. The Sifam Part is C150-BLK
The figure dial is not Sifam but fits reasonably well, is is numbered 0 to 11 with 30 deg indexing. RS Part is 468-0644 and priced at 55p each.
It all adds up to £20.60 to which P&P and VAT have to be added.
Not a cheap option but I preferred them to thumb wheel and a defective switch is easier to replace. So far I have had no failure of the LORLIN rotary switches, NEVER move them when they are under load, which should not be necessary in the Sussex application.
For tightening the collet knob slotted ring nuts, I found an old wide flat bladed screwdriver and cut a centre square section out using a dremmel grinder attachment.
Those of us you used to change elements in the basic Morphy Richards Irons will no doubt have done this before.

oh nearly forgot - the Black stator labels with the white section for showing the number, these I made in MS Paint to a size when printed that matches the diameter of the figure dial. In the print option set size to 100%. I then covered them with thin self adhesive clear film and applied double sided tape to the back of the paper sheet. A sharp craft knife and a good pair of scissors should enable you to make a fairly decent stator label.

One more thing! - I find using these figure dials is of great benefit where panel space is tight. There is no need to mark around all 12 positions of the switch, in fact you don't do any marking at all! A simple table close by gives the switch position information.

[George G4EUF]

Hello Les,
Many thanks for the info, very much appreciated, my main board is now nearly completed, you may have noticed on the above thumbnail?
You mentioning Morphy Richards irons takes me back a long time, I was apprenticed with Midlands Electricity Board back in the mid nineteen fifties and our small repair workshop had a technician repairing the above and adjusting the "stats" on a Morphy Richards test unit, after getting the correct temp he would cut off the surplus amount of thread on top of the adjusting nut, occasionally I would get to help, O happy days!!!
Again Les, many thanks for the information, I will try and duplicate something very similar to your nice design.
Kind regards.
George.

[George G4EUF]

Hello again Les,
I would be grateful if you could put me right regarding the circuit diagram in the manual for the -bias supply and the 1kHz oscillator.
I have now powered the bias supply and have control of the O/P, however, I have no 1kHz oscillator O/P? Do I assume that the circuit diagram is correct in the manual as I have noticed there is a number of mods involving cutting PCB tracks and putting in links, this I want to avoid at all costs if it is not necessary.
I would have thought that by now that any PCB errors would have been corrected and the version of the PCB that have is now correct??
Kind Regards.
George.

[Top Cap]

Hi George, the original circuit diagram is correct and so is the board. I use the original circuit and very happy with it though some constructors reported drift in amplitude of the 1kHz signal. Someone posted a new oscillator circuit with less drift with temperature and I had a try at re-working the present circuit board to accept this new circuit. However, it was just a concept and I have never tried actually fitting the new circuit to the original board. Mikes original instructions for setting up the 1kHz oscillator are:-
VR1 sets the reliability of the audio oscillator and is adjusted for consistant starting with a good waveform
VR2 sets the amplitude applied to the grid (about 105mV)
VR3 sets the grid voltage (read on the grid DVM).
Have you tried this? Ideally you really need a scope for checking this but you may be able to feed the output into a small amplifier or high impedance head phones for test purposes.
Les

[George G4EUF]

Hello Les,
Thank you again for your reply, yes I do have a 60mHz scope and monitoring the o/p pin I do get a very brief oscillation for about half a second when I tweak VR1, but then it disappears?
Bye the way, my negative supply voltage is 36 volts as I am using a transformer from the junk box.
Will take a look again to see if I have made a stupid mistake and look at the voltages around the circuit.
Again thank you Les.
George.

[George G4EUF]

Hello All,
Has anyone else had a problem with the 1kHz oscillator for the "Sussex" valve tester? no matter where I set VR1, there is no 1kHz o/p at the S pin on the board, anybody got any suggestions please.?
George.

[Top Cap]

Is the -8.2V supply ok derived from the zener diode?
The only voltages I have for this circuit were given to me by Mike.
Check for any solder bridges, we have all been there

[mole42uk]

Originally Posted by George G4EUF

no matter where I set VR1, there is no 1kHz o/p at the S pin on the board, anybody got any suggestions please.?

I'm sorry George, I have no ideas, mine worked first time. I can only echo Les's suggestion about checking the voltages. If it squeaks briefly, there can't be too much wrong with it, maybe a component with the wrong marking?

[George G4EUF]

Hello Les and Richard,
Thank you both for your replies, the voltage on the neg supply rail is only 5.3 volts, however, with removal of TR7 the supply rail goes to 8.2 volts.
The voltage across R21 with TR7 in place is around 5volts which suggests to me that TR7 is turned very hard on and is drawing quite a lot of current.
With TR7 removed, as I said the neg rail is normal at 8.2 volts.
If the oscillator was running and with TR7 removed I would have expected to see a trace on the scope at the collector of TR6?
I have studied under a magnifier to make sure I have no solder bridges, I have also tried replacing both TR7 and TR6 and again with no response.
No other part of the board is powered except the 36 volt input to the grid supply part of the circuit and I have complete control of the o/p for the neg grid supply.
Thank you Les for the enlarged diagram of the oscillator part of the circuit, can I trust the voltage reading printed on the diagram as these do not entirely agree with what I am seeing on the board?
Thank you both once again.
George.

[mole42uk]

Hi George, if you remove TR7 and connect the 'scope to the output of TR6, do you still see a brief oscillation when you first apply power?
Is R17 actually 300k?

[KeithsTV]

If the supply rail drops when TR7 is fitted check the value of R27, the feed resistor for the 8.2V supply. If this is too high the extra current when TR7 is fitted will cause the 8.2V supply to drop as there would be insufficient current through the zener for it to regulate correctly. R27 should be 2.7k.

Keith