The "Sussex" Homebrew Valve Tester.

[vidjoman]

R6 mystery component. On the original PCB layout shown in manual page 26 R6 is not fitted. I can not see it fitted anywhere else. It is shown on the circuit diagram and parts list and also mentioned in conjunction with the 5/50 ma switch calculations but not shown fitted on the switch.
I notice that it is shown on the latest PCB design by Decatron so I'm thinking it should be there and not missing from the original board.
I now have my "Sussex" basically working and testing an ECC83 shows the anode current correctly but no Gm reading. Am I right in thinking this might be a non-working oscillator?
Any thought on the above gratefully received.

[mole42uk]

R6 sets the current limit for the MosFET TR2. If the volt drop across R6 rises enough to switch on TR3 the FET will turn off. It isn't really necessary because the resistors associated with the Electrode switch are effectively replacing it. R6 does set the maximum current if the switch becomes disconnected for some reason.

If the oscillator isn't working you won't get a gm reading. But I had a faulty-from-new AC meter which stumped me for a while. Measure across your AC (gm) meter with your multimeter set to 200 or higher millivolts and see if there's a reading.

You could also probe the output of the oscillator at C8 to see the waveform on your oscilloscope.

[vidjoman]

Thanks for the reply Richard.
I will fit R6 even though it's in parallel with the other parts on the switch.
Hadn't thought of a dud meter so I'll try your suggestion. Thanks.
Unfortunately my scope hasn't seen light of day since we moved 7 years ago so it'll probably need a good going over before use.

The only other fault I had was the diode across Relay 1 coil is shown the wrong way round in the layout diagram. Quickly sorted that one out.

[vidjoman]

Working now, thanks for guidance. Found the problem with the oscillator to be the two transistors. List shows BC307 but I didn't have those so looked at my books of transistor listings to find a BC 207 listed as equivalent. I've got about 20 of those so fitted them instead. When I checked today I find the ones listed are PNP but metering the ones I have they are NPN. Double checked and the book is wrong. Fitting another type cured my problem. Only other adjustment was to trim the anode current reading by fitting another 1 ohm resistor that is point one of an ohm higher. Now the reading matches 2 multimeters.
Only other thing to do is change the 1.4 volt stabiliser for the LM317. I'll post pictures later.

[vidjoman]

Couple of pictures - you may notice that I have used a lot of heatshrink and that is for two reasons. 1, It adds mechanical strength to the joints especially as this is a hinged case. 2, It holds in place the ferrite beads that are fitted to each switch tag and each valve holder pin. Also added is a bank of small relays to switch the heater voltages, rated to handle 10 amps it saves the possibility of wear or overheating on the switch contacts. These relays are powered by a small transformer (the blue one in the base) which also powers the cooling fan. I could have used the existing transformer but decided to not add extra load on that one.

[Top Cap]

Looking Good!

[vidjoman]

Question on valve readings obtained on my Sussex Tester.
If I look at the spec given in the Avo valve data manual and follow the settings, with known good new valves I get similar Gm and A current readings to the book +/- about 20%. I assume this is probably normal production spread. What I want to know is at what point do I discard the valve as dud ? +/- 40%, +/- 50% perhaps?

In the past my access to testers were of the simple kind that gave pass/fail without any form of reasoning.
Thanks for any input.

[Top Cap]

See post 1319

[vidjoman]

Thanks Top Cap. Missed that one somehow.

[Chicoull]

Hi all.

I was looking for a Valve Tester, found this link and was instantly hooked! I have started ordering component parts - PCB and transformer already organised.

Tried to source the meters using the info in the manual, but no joy. I would appreciate a working link to a source if possible. The ones I have found on eBay are all from China and require a DC Power Supply. Given that I will be using the recommended transformer with three 6V outputs, I am looking for AC powered meters. The alternative I suppose would be to introduce a bridge rectifier circuit, but I want to stay as true to the original as possible. Any hints would be most welcome.

Regards, Charles.

[David G4EBT]

Originally Posted by Chicoull

Tried to source the meters using the info in the manual, but no joy. I would appreciate a working link to a source if possible. The ones I have found on eBay are all from China and require a DC Power Supply. Given that I will be using the recommended transformer with three 6V outputs, I am looking for AC powered meters. The alternative I suppose would be to introduce a bridge rectifier circuit, but I want to stay as true to the original as possible.

Welcome to the forum Charles. When you say 'true to the original' the original 'Sussex' as it's become known, designed by the late Mike Rowe, has been considerably modified and refined based on the experiences of those who have built it, as you will discover if you read some of the posts along the way. I don't think any two Sussex's will be identical, so 'originality' doesn't really enter into it.

As to digital panel meters, there are three basic types:

1) Two wire meters: These take their power from the voltage being measure, and don't need a separate voltage source to operate.

2) Three wire meters. These do need a supply voltage in addition to the voltage/current being measured, but will happily share a common ground.
This link shows the wiring arrangements:

https://www.bing.com/images/search?q...ao0&ajaxhist=0

3) Four wire meters: These need a separate power supply to operate, which is quite broad - from about 4.5V - 30V, but must not share a common ground with the circuit being measured.

The challenge is to find three meters which are identical in appearance and colour of digits to measure 200Volts DC; 200mV DC & 200mV AC.

Hope that helps clarify a few points.

I'm sure many other Sussex builders will have come up against this and found a source, so good luck in your quest and every success with the project.

(I haven't built a Sussex - I have a Taylor 45D, so don't need to. (It's illustrated on page iv of the manual).

[mole42uk]

Originally Posted by Chicoull

Tried to source the meters using the info in the manual, but no joy. I would appreciate a working link to a source if possible.

I think all of us used Chinese meters - this is an example: http://www.ebay.co.uk/itm/3-1-2-Blue...QAAOxyVPJSKblY and the others all conform more or less to the same basic specification.
I think if you look carefully at the ebay offerings you will find meters that fit the bill.

Keep posting as you go on, we are a lively bunch who have all built a 'Sussex" valve tester and have many stories to tell!

[Top Cap]

Mods: Can you change the link on post 1 :-
A handbook for this tester can be found here:-
http://homepage.ntlworld.com/lez/Sus...%20version.doc

to:-
A handbook for this tester can be found here:-
http://g4cnh.com/public/Using_the_Sussex_VT1.pdf

ntlworld suddenly took away private work space so I had to find another ISP.

With respect to the panel meters, these can all be found on Ebay but they are advertised as having a 9-12V AC or DC input. I suspect they will also work OK with the 6V AC available from the custom transformer but worth a punt considering the very low cost of these items. They do have to be run from a floating independent supply, especially measuring current or they will fail. I once thought the 200V DC meter would be OK but then realised it is working in reverse to measure the Negative Grid Volts so once again this would need to be isolated. All to do with a voltage limitation between the input -ve terminal and the actual meter supply -ve. When I had these problems before I used to use DC-DC converters for isolation but the noise on the supplies would always present another challenge. Adding more capacitance on the output only caused failure of the converter so chokes had to be used to augment the lower acceptable capacitance values. Give the cheap 9V AC/DC meters a go, the other way is to use some of the cheap multi-meters.

This link will help you find the 200mV AC meter, the supplier also does the others if you search.
http://www.ebay.co.uk/itm/LCD-AC-200...1%26rkt%3D1%26
Les

[Station X]

Originally Posted by Top Cap

Mods: Can you change the link on post 1 :-
A handbook for this tester can be found here:-
http://homepage.ntlworld.com/lez/Sus...%20version.doc

to:-
A handbook for this tester can be found here:-
http://g4cnh.com/public/Using_the_Sussex_VT1.pdf

ntlworld suddenly took away private work space so I had to find another ISP.

Link changed as requested.

[Ed_Dinning]

Hi Gents, the isolated supplies on my Sussex transformer typically give out 7.5v when run on nominal mains voltage and usually operate those meters rated at 9v AC.
If the meter is rated at 12v Dc it could be powered from a rectifier and cap arrangement or even a simple voltage doubler as the current is small.

Ed

[vidjoman]

I've powered mine with a rectifier and 100mfd cap. Inspection of the modules (mine at least) shows a bridge rec on the input and a voltage regulator that probably gives a5 volt supply - I haven't checked it as it all works properly.

[Chicoull]

Thanks for the comments regarding the meter power supplies. I have taken them on board and ordered the Chinese versions. Ed is providing the Transformer and it sounds as if the outputs will be sufficient to power 9V AC. Just a case of waiting for the components to arrive. In the meantime I will get on with the PCB's and panel cutouts.

Charles

[Chicoull]

Hi All, I have been going through the list of components for the PCB to order them and have hit a stumbling block. Capacitors C103, C104 and C105, which are on the board are listed as 100nF, but no voltage value - I have searched the circuit for them and no luck. C106 is not on the list, but is on the board - again no luck with the circuit. Any ideas where these four are located in the circuit and if so, the values?

Regards, Charles

[Top Cap]

My original circuit only used components with a 100 prefix for the additional low voltage heater strip-board e.g. C101, to separate it from the main board components. It did not use anything higher so C103 to C106 is a mystery. However, though the original low voltage heater circuit was OK for me, I remember a much improved low voltage heater circuit being mentioned which probably used those components and is incorporated in the new boards. Its circuit and description may be among the many posts somewhere.

[Station X]

I just had a look at the manual and could only find C100 and C101.

However the voltages for these caps differ depending on whether you look at page 47 or page 50