The "Sussex" Homebrew Valve Tester.

[Jeffreyabb]

Martin
Thank you. That's quite clear. I'm looking forward to that post.
Jeff

[Andymic]

Originally Posted by G8UWM-MildMartin

I'm going to wait until I have received and inspected the PCBs.
Should be in a couple of weeks, but I haven't had the final invoice promised this week yet...

Martin,

For the PCB, did you do the bridge rectifier mod for D1 / D2 ?

[swordholder]

Hello Guys
I have made a small modification to the Sussex valve tester in order to check for gas current.
No modifications are required to the PCB or power supplies.
Basically all I have done is to include a 1k resistor in series with the grid voltage supply to the top panel.
As can be seen from the attached circuit, a relay switches the anode current DVM between measuring the voltage across the 1R in the anode circuit and the voltage across the added 1K in the grid circuit.
1uA of grid current will generate 1mV across the 1k, the grid current can be read with a resolution of 0.1uA.
I have mounted the relay "dead bug style" using double sided tape to the bottom of the case.
Thanks for all the interest shown in the project.
Regards
Mike

[Andymic]

Mike

Can you give me details of the pushbutton used.
I'll add it and the 1K resistor to the BOM

Andy

[swordholder]

Andy,
The switch is Rapid part no 78-0186 push button.
Add an extra 48v dpdt relay to the list

Regards
Mike

[Andymic]

Mike

Added to the BOM.

BTW, I sent a couple of emails to you for some clarification on valve bases and heatsinks.

Do you think it might be useful to update the schematic with the Bridge rectifier mod and this Gas I test?

Andy

Andy

[swordholder]

Andy,
I haven't received any mails, please resend.
There is a circuit already posted for the Gas I addition.
I will do one for the bridge rectifier if anyone is stumped, all that is needed is a couple of additional rectifiers on the underside of the board,
Regards
Mike

[Guitarist28]

Mike (swordholder),
just to clarify, is C2 definitely 630v polyprop?

thanks

Rob

[swordholder]

Rob,

Without stripping out the PCB to check, as I recall this was the case, although in retrospect, I think any plastic type with a sufficient voltage rating should do the trick, it's really a belt and braces component to filter any high frequency rubbish.

Regards
Mike

[Guitarist28]

Thanks Mike,
I have ordered almost all compoments less pcb, transformer and parts for your new mod

Rob

[ahjohn002]

Dear all,
This thread seems to have quieten down quite a bit.
Has anyone managed to complete one tester? Grateful if you can share your experience with me.
Regards,
John

[Guitarist28]

I think that some of us are awating parts hence the lack of activity.


Rob

[David G4EBT]

Originally Posted by ahjohn002

Grateful if you can share your experience with me.

I guess that as soon as all the bits are together, there will be a snowstorm of postings on progress, pitfalls, hints and tips. I've lost track of how many are building the Sussex, but it was clear from the outset that this was going to be a hugely popular project - not simply the utility value of a valve-tester, but such an excellent well thought out and highly repeatable home-brew design in the best traditions of the pre "plug 'n play era".

Already there have been 132 postings and 7,913 viewings of this thread, and I think it's destined to have a longer run then The Mousetrap in the West End. Just another example of what a wonderful forum this is, for which Paul and the moderators deserve much credit.

(The Avometer survey is now up to 509 postings and 48,194 viewings!).

Every success to those who are building the Sussex - I wounder who will be first past the post?


David,
G4EBT

[swordholder]

David,
I'll claim first place !!
Seriously though, I think it should be easlily replicated given that a PCB and Mains Transformer are about to be made available.

Mike
PS I wonder what the most viewings is for a construction project?

[dwhitf47]

Newbie here!

Just wondering if the design can be built to provide a little more current (160ma) without a redesign. I would like to test 6c33c tubes.

Thanks
Darrell

[swordholder]

Darrell,
The Sussex will not test 6C33 without major modifications. The heater supply alone takes 6.6A so neither the power transformer or the switches used will carry that current.
I used to test these when I was working and I used a separate heater supply on the VCM163 and NEVER used the functions switch to switch the heater as even on that tester, the switch contacts are pretty puny.

Regards

Mike

[swordholder]

Hi All,
I have had chance to evaluate Ed's mains transformer, all seems OK
I am attaching a revised circuit diagram to take into account the bridge rectifier and additional heater voltages.
Extra parts required are:-
2 x 1N4007 rectifiers.
1 x 2P 6W MBB switch
Only 5 ways are used. I have included an external heater volts position which isolates the transformer winding and will allow an external heater voltage to be applied via a couple of extra sockets on the case.
I hope this makes sense

Regards
Mike

[Radio_ham]

Hi Mike,

I'm new to this forum and I am personally highly interested in building the VT1. However, unlike many in this forum, I am not too familiar with tube tester circuitry. Thus, may I ask you please some additional explanations on the following topics:
* some details on the role of the FUNCTION SWITCH in particular with respect to its positions 2 (ANODE S/C) & 3 (GRID2 S/C ),
* the role of the BC237 transistor circuit,
* the VR1, VR2 & VR3 settings to be made,

Hoping not to have abused your kindness- Many thanks es vy 73.

Dan

[swordholder]

Hi Dan,
First let me explain the BC237 circuit. The emitter is at -ve voltage, and the base is tied to -ve. The transistor is cut off and the LED is off.
If either the anode or G2 has a leak to ground, (+ve with respect to emitter & base) a positive voltage will appear at the base and the transistor will conduct lighting the LED. The higher the +ve voltage (the lower the leakage resistance) the brighter the LED.
The leak to ground will be either through the grid or suppressor grid.
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).
Hope this answers your question

Mike

[Radio_ham]

Hi Mike,

I wish to thank you for the rapidity and the clarity of your response.

I am going to gather the components (some of which are not available on the local market ) and I will begin the construction soon after.

All the vy best.

Dan