The "Sussex" Homebrew Valve Tester.

[jakamp58]

How about part number. 815820 - 89 or similar toolcase at http://www1.conrad-uk.com/scripts/wg...max_results=20

for a case? You have them with plywood at the inside, so you can glue supports into the case to mount all the hardware.

Jan

[Guitarist28]

Hi all,
Please note that D6 & C8 are orientated the wrong way aound in my xray diagram that I posted from an earlier post to this thread (thanks Andymic for spotting D6)

Regards

Rob

[Guitarist28]

I've lost the will to live.
I've swapped D6 around and its still not right - the values for TR6 and 7 are still low! Am I measuring from the correct place (0V at AB)??

Rob

[FRANK.C]

Hi Rob
If your using a 9V battery to test the oscillator it might be best to lift one leg of ZD10 to take it out of circuit. Then apply the battery directly across C3. You can then take measurements with the negative lead of your meter. The positive lead clipped to the positive of the battery. The readings that you will get will be slightly different to Mikes because of the higher supply voltage from the battery.

Frank

EDIT:
Sorry should have said take measurements with the positive lead of the meter and connect the negative lead to the battery positive

Frank

[Guitarist28]

Hi Frank,
Thanks for the advice - I'll try this tomorrow and post results accordingly.

Regards

Rob

[Guitarist28]

I followed Franks advice and removed a leg from ZD10. The readings seen were as follows:

TR6 - Coll -3.16, Base -0.65 & Coll -0.05
TR7 - Coll -OL, Base -OL and Coll -2.43

Is TR7 getting to much of a wallop from the 9v battery or do I have another problem in the circuit??

Regards

Rob

[FRANK.C]

Hi Rob
I'm not sure about your readings as you have 2 coll. for each transistor and no emitt. Each base and emitter should about .6V apart if they are substantially more than that the transistor may be open circuit. Although looking at the one reading that you have for TR7 it appears to be passing near the right amount of current (assuming the second coll. is actually the emitt). Are you sure the probes are making good contact when measuring TR7 coll. and base.
The voltage measured at TR7 coll. should be equal to the voltage across the battery.

TR6 voltages looks OK

Frank

[Guitarist28]

Hi Frank,
The figures should read coll/base/emit and coll/base/coll (I was in rush to go out when I posted!!).
I'll have a go at TR7 again

Rob

[Station X]

According to your last post you still have a transistor with two collectors.

[Guitarist28]

Sorry Graham et al.
I must learn not to post whilst I am about to leave the house to go to the doctors/physio/swim in future.

What I should have written was as follows:

TR6 - Coll -3.16, Base -0.65 & Emit -0.05
TR7 - Coll -OL, Base -OL and Emit -2.43

I am going to take the readings of TR7 again.

Regards

Rob

[Guitarist28]

I finally managed to get of reasonable readings from TR6 & 7

TR6 E -0.06, B -0.68 & C -1.64
TR7 E -1.04, B -1.56 & C -9.24

I assume the results will vary depending how good a connection can be achieved on C8 which not easy as I trimmed the leads really short. I really need to get to grips with some basic circuitry understanding so I think that a lot more reading will be in order.

Regards

Rob

[julie_m]

(I was going to ask this in a PM, but I thought it relevant and interesting enough to post openly.)

I note you say that your selector switches are set up "the same as the AVO CT160". What exactly does that mean? I'm taking it that there is one switch per valveholder pin, and each numbered position is one of the test voltages; but what is the meaning of each numbered position?

I ask because I'm building my own valve tester, not quite to your design (diversity is A Good Thing™) but some measure of compatibility is A Good Thing too. I'm thinking the easier it is to adapt a test schedule written up with one model of valve tester in mind for another tester, the better.

[Top Cap]

Attached a rough and ready copy from the AVO manual which may be of help.
Les

[julie_m]

Thanks; that makes perfect sense!

[Guitarist28]

At last, my circuit board is indeed oscillating (see attached) although needs a little tweaking to be perfect.

The case now to be built......

Rob

[thor1961]

Are "US" transformers still available if so what is the cost and how can I purchase one?

[Ed_Dinning]

Hi Thor, I've wound some for the US market, cost is exactly the same at £50.
Primary is 115, 120, 125 and an extra 2.5V tap is added in the heater winding to cater for the audio triodes.
Postage costs are typically about £40 for surface freight and £70 for cheapest airfreight.
It may be cheaper to have 2 or more wound and reduce the cost that way. PM me if you need more details.

I will keep these transformers available for the foreseable future

Ed

[Top Cap]

This is my effort so far, still waiting for my bonus at work to invest in a case and meters . I decided to use fan assisted cooling to keep the heat sink smaller, this being run from the 12V heater supply. You can see the additional rectifier and capacitor mounted between the relays on the piggy back board. I might fit a thermostat to the sink wired to the HT relay so if the fan fails and the sink over heats then the HT will be cut off. I also considered servicing if any of the devices fail so decided to modularise the whole thing, interfaced with a 50 way D connector. The photos show the whole prior to wiring, just hope it looks just as neat when it is fully wired up.
When full construction takes place I am considering wiring all G1 wiring with single core screened cable. Also using 9 separate screened wires between the pin selector switches and the valve holders. The latter I hope to wire with spaced standard single wire but I happen to have a bag of ferrite beads so may be tempted to fit one at each valve socket connection. Hopefully this may stop any tendency for parasitic oscillations, or am I going a bit OTT?
Les

[Andymic]

what a damn fine bit of construction.
Well done!

[MichaelR]

Les ,

You Have done the design justice with that neat construction, very professional.

For the sake of minimising parasitics I am going to use screened cable as well, there is nothing worse than trying to cure parasitics when you have them in circuit.

Mike