The "Sussex" Homebrew Valve Tester.

[Top Cap]

Hi Graham, I originally used 16V as the circuit runs from the 5V tap on the transformer.
No harm in using higher voltage ones except for physical size. There were various BOM recommendations and this is probably how the two voltage ratings became stated.
Still think 16V is fine. I have looked over the majority of the 1300 posts :-( but have not managed to find the LM317 circuit for Chicoull if indeed that is the circuit using the unknown C103-C106.

[Top Cap]

Just found a pdf of a re-drawn Sussex circuit using two LM317 for heater supply, located on right hand side. I believe this circuit is now embodied on the latest batch of circuit boards. This was done after the Sussex Manual was produced hence why it is not shown.

[vidjoman]

I think those parts (C103-106) might from the NEW PCB listing or part of the modified heater regulator. This may cause some confusion if that is the case.

[Chicoull]

Hi Top Cap,

Thanks for the link to the schematic. I looked back thru the posts and see that Martin from Sweden submitted it when posting drawings of the new PCB. I have sent him a PM, requesting some guidance on the values. I will update if I get a reply.

[Chicoull]

Hi all,

Got a very prompt reply from Martin. He tells me that the values of C103 to C106 on the new PCB are all 100nF and at least 25V.

[marty_ell]

Hi Forum

I've been studying the Sussex V. T. circuit with a view to building one of these as a winter project.

I'm having difficulty understanding how a directly heated rectifier such as 5U4 is tested - what would normally be the cathode connection on pin 8 is one of the heater connections. But Sussex's heater supply is floating wrt. system 0V. So there is no 0V connection to the valve - how do the anode currents flow?

I'm probably just being thick; please can someone put me right.

Cheers, Marty

[vidjoman]

Marty - I fitted a small switch, shown in photo on post #1020, which operates a relay with high current contacts to select direct/indirect heater use. Also required for some low voltage battery valves.

[David G4EBT]

I get a '404' error message when I try the websites in posts #198/199 above.

[marty_ell]

Thanks vidjoman!

With pencil, paper and a lot of coffee I've figured out a directly heated valve's anode current flows through the heater-cathode insulation LED (the Construction and User manual comment 'LED will light when directly heated valves are tested' should have given me a clue!).

As I'm planning a higher spec tester, with higher current tests for rectifiers, your relay suggestion is appreciated.

Cheers, Marty

[ColinTheAmpMan1]

Originally Posted by David G4EBT

I get a '404' error message when I try the websites in posts #198/199 above.

Try this URL. It is for the pot mentioned in message #200.

https://www.rapidonline.com/vishay-5...ometer-65-1060

Colin

[Chicoull]

Hi all, Latest PCB has been built (see pic). Starting to cut metal, so soon to begin internal wiring. Ferrite Beads have been recommended in past posts. Given the 1.2mm size recommended on the BOM, I assume that they are fitted to the stripped wire and heatshrunk? Is it only the Pin Selector Switches and Valve Holders which require them? If so, would that be every single daisy chained wire - approx. 250 beads?

Regards, Charles.

[vidjoman]

I fitted ferrite beads to each valve holder pin and each tag on the pin switches. The daisy chained wires only getting 1 bead, mostly with 2 stripped wires running through and held by heat shrink. The heat shrink also acts as an extra insulator to stop the possibility of wires touching. I think it was a good idea as I have not had any instability experienced by others. Worth doing as you go as it'll be difficult later and they are very cheap - got mine from Rapid. You can just see the beads and heat shrink in my picture on post #1325

[mole42uk]

Absolutely, the ferrite beads are a good idea if not essential. You need to loop the valveholder pins, in other words, make a connection to the first valveholder pin 1, then the next pin 1 etc etc and at the last valveholder, take the connection back to the origin to make ring. One ferrite bead is all you need on the ring.

You also will probably need a grid stopper resistor close to the Octal valveholder, mine used to oscillate when an EL34 was tested until I did that. Can't remember if that is on the circuit diagram or not.

[vidjoman]

I've not had any problem with EL34, 6L6 and similar. I did use a ferrite bead on each pin of each holder not just one per per pin number.
For ease of following - I used wires that follow the resistor code - pin 1 = brown etc.

[Bobdger]

I always use the resistor colours for cable / pin numbers. It works for me..
Bob

[Jon_Hols91]

Hi All,
Been studying the thread and circuit for a little while now but just recently joined. I have contacted Martin for the PCB's and Ed for the transformer and am really excited to start my build. I'm sure I will be posting questions once the components start arriving.

Anyways, just want to introduce myself and share my enthusiasm and gratitude toward those who have put so much effort to developing the Sussex VT. Such a great project and no doubt a very useful tool!

Thanks,
Jon

[Chicoull]

Hi all, thanks for the inputs. great idea to use colour coding on cable. have finished cutting the panel and have created a face template for the switches etc. Was checking I have labelled correctly and came across the following in the user guide:

19. Cathode/Heater biased toggle switch (SW17) used to check the insulation between Cathode and Heater. The switch is normally biased OFF to remove the -40V test voltage from the heater circuits, especially important when testing directly heated valves.
20. CAL Switch (SW18), used to set up the gm meter. In its CAL position the test signal from the oscillator board is set, using VR2 to give 100mV on the meter. The switch is then set to its Normal position for measuring the signal present on the Anode of the valve under test. As the same meter is used for both measurements then the results are relative to each other and negate the requirement for using an additional Voltmeter.

These switches do not seem to appear in the circuit diagrams or panel drawings. Have I missed something?

Charles.

[Chicoull]

Further to my last post...when my template is fitted to the face panel, I will be able to start installing switches, valve holders etc. Looking at the wiring between the pin switches and valve holders, it appears that the nine cables are screened - is that correct? if so, will standard microphone wire do, or more heavy duty satellite cable? The screens are all linked together and output to "a" - is that the board earth connection?

Charles

[Top Cap]

I think these items were a suggestion from other builders, I did do some sketches of possible implementation but were never tried by myself.
I will append the sketches I have, you should be able to see where they fit on the main circuit diagram. Maybe others can comment on these two changes.
If implemented, the signal amplitude control VR2 would ideally have to be re positioned so that it was easily accessed from outside.

[vidjoman]

Where in the manual are the instructions you mention above. Can't find them in my version. The cables between the switches and valve holders should be screened so as to reduce and stray crosswalk. Microphone cable will be suitable if adequately voltage rated, remember that there will be up to 300 volts used.