The "Sussex" Homebrew Valve Tester.

[Doris The Diode]

Originally Posted by Ramonthebiker

Hi Berni - I am very interested in your 'Junior' - I started out on this project some years ago and now with the COVID19 lockdown it seems as good a time as any to get back into it! Have you a slimmed down circuit diagram you could share? best regards and stay safe, Ramon

Hi Ramon,

Sorry for the delay, I occasionally pop in here to have a look.

Regarding the circuit, I can dig up the diagram and post it here, not sure if I will be going off topic. If I am then we can get in touch via PM or email.

Basically I bought the transformer off Ed who is on this forum and in this thread, he makes the transformer for the Sussex and I highly recommend buying this from him as I searched hi ans low to find something similar and could not. You can use other transformers but you will end up perhaps with a few to do the whole job, good if you have space, I didn't.

Circuit - The Junior has the transformer and both circuits for HT and Screen, the grid circuit but no oscillator. I do not have any relays and use a switch in the HT to turn on and off the HT. I also do not use all the heater voltage outputs as I did not have space to put extra banana plugs but you might be able to. I use only 6.3v and 5v as these are the main valve heater supplies I use, so it is specific to my requirements but you could drill a few more holes and have the lot.

I'll try and draw something up and post it.

All the best,
Berni

[nemo1956]

Hi there. I'm very interested in this project.
I was wondering if there is a kit.
The other problem is I live in Thailand.
De HS0ZLQ /G0MIH

[Richardgr]

I am planning on using an external PSU for heater supplies, and I have small PCB transformers for the meter supplies.
Can I have a single supply for bias, screen and plate? I am considering a 200 VA torpid, with a 33-0-33 secondary, with a voltage quadrupler.

[alexander-fa]

Hi everyone.

I bought last year the PCB's (one main and four small for selector switches).
I think it is the last version, on the back says: Sussex valve tester by Martin Forsberg Sweden
I am very confused with the component list, no correct BOM found,
Does anyone can help?
I'll appreciated
Best regards
Alex

[Radio Wrangler]

Hi Alex, and welcome!

Just look back in this thread for member "Dekatron" - the member's name in this case not the number of posts indication, which is also Dekatron for some people. This is Martin Forsberg's user name.

Click on his name and you'll get a drop-down menu, and from here you can send him a personal message. The forum will send him an alert email if he has the facility turned on.

You could also click "find all posts by...." and then scroll through that list and you'll likely find one with the BOM attached.

David

[Dekatron]

In post #1477 you'll find most files for the CB, including a schematic with all component values bythe components: https://www.vintage-radio.net/forum/...postcount=1477

In this post I've included a PDF-file with just the BOM taken from the schematic in post #1477. Now, I've never built a Sussex myself so I can't say if it is correct or not but it was exported from the Designspark file.

Forum user G8UWM-MildMartin sold the PCBs, maybe he is still selling them, and he should have a BOM too.

[Radio Wrangler]

Thanks, Martin

David

[alexander-fa]

Thanks a lot! Now thinks are more easy..
I have one more question, I've noticed there are same parts in main PCB and selector PCBs, for example C1, R3, R5, R6, R7...
Should I use both or only one of them?
May be silly question, but I think is better asking
Best Regards
Alex

[Dekatron]

The BOM in post #1586 is only for the main PCB, there are no BOM files for the switches, all component values for the switches are in the files in post #1477 in the circuit diagrams.

[alexander-fa]

Thanks Martin, I've noticed that after posting.
Best regards
Alex

[Dekatron]

The reason why I didn't adjust the component numbering was due to the version of Designspark that I made these PCBs on didn't work with multi-sheet schematics with component numbering streching over deiffernt sheets. I discussed it with some people here on the forum and decided to keep as much as possible original when it cam to numbering, but the switch PCBs were also added after the main PCB was finished.

In the future anyone who wants can convert them to a modern version of Designspark if they want and then change the numbering while using multi-page schematics that are connected.

[Chris55000]

Hi!

I've been thinking about the construction of this unit, and the fact that the power input and the sense input of the original LCD panel meters shares one connector suggests to me that terminating the four 6V mains transformer meter supply secondaries and the meter connections in in a simple "junction box" connector PCB will allow simple 4 way leads and plugs to run up to each meter module, with additional 2 way leads and plugs to carry the meter inputs to the main Valve Tester PCB – the design I suggest is intended for Martin's PCB that carries 2–pin connections for the meter output connections!

I thought of this as a way of making the interconnecting wiring a little simpler and neater, that's all!

I'll get this drawn up & design files with Gerber's posted in a day or two!

Chris Williams

[ColinTheAmpMan1]

Originally Posted by Chris55000

Hi!

I've been thinking about the construction of this unit, and the fact that the power input and the sense input of the original LCD panel meters shares one connector suggests to me that terminating the four 6V mains transformer meter supply secondaries and the meter connections in in a simple "junction box" connector PCB will allow simple 4 way leads and plugs to run up to each meter module, with additional 2 way leads and plugs to carry the meter inputs to the main Valve Tester PCB – the design I suggest is intended for Martin's PCB that carries 2–pin connections for the meter output connections!

I thought of this as a way of making the interconnecting wiring a little simpler and neater, that's all!

I'll get this drawn up & design files with Gerber's posted in a day or two!

Chris Williams

I think I may be reading this incorrectly, but please bear in mind that the supplies to the meters must be independent, as stated on P14 of the manual.

I might well get around to some construction of mine, but there is so much on the "round-to-it" pile that I can't make any predictions. Perhaps lockdown for a few more years? (only joking!).

Colin.

[marcoamf]

Hi!
I have built the tester and I was able to correctly test 12AX7s (dual triode).
However, all tests with power tubes (tetrodes and pentodes) presented weird results that I'm questioning (especially because some of these tubes are being used in amps with no problems at all; no identifiable noise, pops or anything).
None of them present any shorts.
When in test mode, plate current and transconductance numbers increase gradually (but faster than when measuring triodes) up to around spec numbers and then grow faster. Current stays quite unstable, varying between 1.5x to 3x spec plate current.
Transconductance also gets unstable, varying from 5x to 10x spec transconductance.
Tubes warm up really fast and I can assume they're hotter than they should (no red plating, though. I didn't wait too long, however, hoping I don't blow these working tubes).
All of them fail GAS test (numbers very different from zero). In most cases, display shows 1 (above meter range).
I have tested 4 different (but old) EL84s. These are quite old, so I expected something wrong, but more on the low current/transconductance side, even though I use two of them in an amp.
2 different KT77s. JJs, were working fine until about 5 years ago.
1 6L6gc (JJ).

A friend had tested my tester and said it was working fine.
Would anyone have a guess about what could have happened and what kind of issue I should try to look for to troubleshoot? (and how to check)

I would guess it's something related to the screen part of the circuit (since 12ax7s are testing fine), maybe a zener that is not limiting what it should limit...

any help is much appreciated.
Thank you!

[Ed_Dinning]

Hi, try checking the heater voltage applied to the valve is correct with a good meter. This can vary a lot if your mains is also varying. The transformer I designed for the Sussex has multiple primary taps to get over this problem, but will not compensate if the voltage is varying rapidly, or if the mains waveform is poor (not sinusoidal) as can happen with heavily loaded power systems.
For accurate results a true RMS meter is needed.

Ed

[Dekatron]

Did you use ferrite beads on all wiring for the valve sockets?

Have you tested with a grid stopper resistor?

It could be that the valve under test is oscillating which can result in strange behaviour when measured, it can even affect the tube tester so that it doesn't regulate the voltages correctly and even affect the oscillator used to drive the grid.

[Top Cap]

Originally Posted by Dekatron

Did you use ferrite beads on all wiring for the valve sockets?

Have you tested with a grid stopper resistor?

It could be that the valve under test is oscillating which can result in strange behaviour when measured, it can even affect the tube tester so that it doesn't regulate the voltages correctly and even affect the oscillator used to drive the grid.

I second that, whilst testing the valve and getting strange results, try placing your hand around the glass envelope. If it causes changes then the valve is oscillating. In the past I have used a few turns of Grounded wire wrapped around the envelope and moved this loop up and down to stop the oscillation. This is only a problem I find with valves like EL34 and some KT88's. I may try fitting a grid stopper in just the octal base for these valves and hope that other valves tested in the socket are not affected by the resistor.
Les

[marcoamf]

Originally Posted by Ed_Dinning

Hi, try checking the heater voltage applied to the valve is correct with a good meter. This can vary a lot if your mains is also varying. The transformer I designed for the Sussex has multiple primary taps to get over this problem, but will not compensate if the voltage is varying rapidly, or if the mains waveform is poor (not sinusoidal) as can happen with heavily loaded power systems.
For accurate results a true RMS meter is needed.

Ed

All voltages (including heater) are correct (at least when no tubes loaded). I'll test voltages on other socket with tube loaded. I assume I should always measure voltages in "Test" mode.

[marcoamf]

Originally Posted by Dekatron

Did you use ferrite beads on all wiring for the valve sockets?

Have you tested with a grid stopper resistor?

It could be that the valve under test is oscillating which can result in strange behaviour when measured, it can even affect the tube tester so that it doesn't regulate the voltages correctly and even affect the oscillator used to drive the grid.

Hi,

No, I'm not using ferrite beads.
Your hypothesis makes sense to me. How can I use a grid stopper resistor? Just in series with the grid connector or should there be a grid leak to ground?
I assume the grid stopper resistor value would be tube-specific. So, how to determine the value for each?

[Dekatron]

I'd start with using ferrites on all wires, it has been discussed here in this thread and it was AVO who patented the meathod in their valve testers a long time ago.

Grid stopper resistor comes second after ferrites, from a few kiloohms up to tens of kiloohms is usually enough and in series with the grid wire close to the socket.