The "Sussex" Homebrew Valve Tester.

[George G4EUF]

Hello Richard and Keith.
Yes, R27 is definitely 2.7k and R17 300k, with TR7 removed and the scope connected to the collector of TR6 and tweaking VR1 from one end to the other I do get an occasional osc but does not continue to run
I have very carefully checked the values of all the components in the circuit and I am somewhat at a loss to know where to go now?
George

[mole42uk]

That is odd.
I'd need to probe around mine to get any useful clues, but it's at work and I'll not be there until Tuesday.

[George G4EUF]

Thank you Richard.
Regards.
George.

[George G4EUF]

Hello Richard, Les and Keith,
Success!!!! having gone round the circuit board AGAIN! checking the value of components, I found that R18 was 221 ohms and not 10k, these were bought from Maplins and of course they have the 4 band colour coding which I hate and no one as yet has explained to me why manufactures have done it.
I am really kicking myself for nine times out of ten I always check the value on a meter before fitting in the board, but having trusted Maplin I thought these were the correct value and did not bother to read the colour code as a result I am really angry with myself. You live and Learn.
Thank you all again for your help, really appreciate it.
George.

[KeithsTV]

Well done.

I often check the values of resistors before fitting them as the colour bands on modern parts tend to look similar especially brown and red!

Keith

[Top Cap]

Well done George, I was thinking it had to be something like a wrong value somewhere, like Richards oscillator, mine worked first time too. A little rule I apply to myself with 4 band colours is to mentally add the next colour up on the 4th ring. Thus a Brown ring will indicate that the value is in the Red range i.e. 1 to 9.9k, likewise an Orange ring indicates that the value is in the Yellow range i.e. 100k to 990k. Sounds crazy but it works for me .
It's all part of an extended range so you can have such things as 1.52k, sometime I think HP and Tektronix started all this, just look at some of their circuit diagrams
Les

[mole42uk]

Excellent news! I have to say that, these days, I check every resistor before fitting with one of those cheap digital LCR meters - it saves such a lot of hassle especially since my eyes are nowhere near as good as they used to be.

[ribbonmicsrus]

I was looking through the build instructions and at the end there were case styles from various members. One I particularly like is by David Benson, is he still on this forum or does anyone know the manufacturer / part number if still available.
Andy

[vidjoman]

I mentioned the details in the Sussex main discussion. Think it was around post 1000. Also showed some pictures of the construction and the time when the glass roof of my conservatory was smashed in the storms of 2013.

[ribbonmicsrus]

Thanks for that, found details, not in stock till around middle of April

[vidjoman]

The parts will need to be very carefully arranged to fit into this case. There's not a lot of space,but it can be done.

[G8UWM-MildMartin]

Gentlemen and Ladies,
I'm embarrassed, pleased, surprised, and relieved to have sold the last of the batch of 15 PCBs to the late Mike Rowe's original design ordered in June last year.
They cost me £7.07each + £15 post +VAT= £9.684 each.
If I order another 30, they would come out at about £5.76 nett (£7.52 gross)
Again, before ordering them, I would really like someone to offer an improved version and either arrange for its production and sales, or contact me to fund it for production by P&M Services and for that person to either handle sales or negotiate a royalty from me.

I'm also considering offering them as part-built PCBs with all components fitted except the MOSFETs, and the oscillator tested, as I like building things and the components are probably cheaper in quantity than just the postage for small quantities from the different suppliers.

Coments welcome.

Thanks,
Martin.

[George G4EUF]

Hello Les,
Either I am going potty but is there a mistake in the diagram on page 29 of the manual, fig 31, which shows heater line + going to pin 4 of all the selector switches, surely it should be 2 for + and 3 for - also cathode is connected to pin 2 and it should be pin 1?
Would appreciate your views?
Regards George.
Will upload a picture of my version of the tester so far.

[mole42uk]

Hi George.

I'm not sure here, it's a year or three since I built mine, but the wiring to the switches is dependent on matching the AVO layout so that the AVO charts work. Don't forget that the valveholder pins are connected to each switch pole, so that, for example, if switch three is turned to '4' then pin 3 of the valveholdes are connected to the H+ line.

Hope this helps,
Richard

[George G4EUF]

Hello Richard,
Thank you for your response, yes I am to following the AVO listing, ie: the settings for the EL91 show, 412 360 500 and if you follow this thru you find switch 1 position 4 is connected to the grid which is pin 1 of the valve in question, switch 2 position 1, is connected to pin 2 of the valve which is cathode, etc.
Not sure if I have got it all wrong, but await your advice, many thanks Richard.
Regards George.

[G8UWM-MildMartin]

Hello George,
I can't see anything wrong:
Knob marking 0 = pole (contact) 1 of switch = o/c
Knob marking 1= pole 2 of switch = cathode,
Knob marking 2 = pole 3 of switch = H-
Knob marking 3= pole 4 of switch = H+ , etc.
Regards,
Martin.

[mole42uk]

Yes, I think Martin has it! I'd forgotten about the "0" position which shifts all the switch contact numbers around by 1.

[George G4EUF]

Hello again Richard and Martin,
Yes, I totally agree with the switching diagram on page 19, fig 22 and is exactly what you say Martin, however, my query was with regard to the circuit diagram on page 29, fig 31 which shows the + heater line going to tag 4 of all the selector switches and the cathode line to tag 2 of all the selector switches, surely, unless I am going daft but should it not be tag 1 for cathode and 2 and 3 for heater?
Regards George.

[Top Cap]

Hi George, I believe the Page 29 drawing is correct, tag 1 of each switch is not used as it is an open circuit position. So from then on each tag will be numbered +1 and remember that position 1 of each switch will be shown as 0 on the front panel. So switch position 1 (Cathode) will be connecting to switch tag 2, switch position 2 (Heater -) will be connecting to switch tag 3. Hope this helps. Les

[George G4EUF]

Hello Les,
Thank you for your reply, my confusion has come about because I simply chose to ignore the 0 position as there is no connection, however, it is still counted despite there being no connection to tag zero, my mistake, it did not make any sense to me looking at the diagram on page 19, fig 22 which having taken look at the AVO switch settings for the EL91 which shows, 412 360 500 which I found to be correct on that diagram and my confusion occurred with the diagram on page 29, fig 31 which shows the heater + connection going to pin 4 on the selector switch.
However I think I have now got the drift of it.
Many thanks Les for your help and encouragement, incidentally, I have tried to upload a picture of my version of the tester, somewhat similar to yours, however, for some unknown reason it does not appear on the site?
Again my thanks Les.
Regards.
George.