The "Sussex" Homebrew Valve Tester.

[ricothebrol]

Hi,
That tube tester is an amazing project !
I have two question, please forgive me if it has already been answered (I didn't go through the whole 60 pages thread and didn't find a "search within thread" function) :
- is the 300V/95mA plate supply high enough to correctly test high voltage tubes like 6550, that are generally used at twice that voltage (600V is pretty common in big bass amps like Ampegs and so). I guess some tubes pass at 300V but fail at 600V...
- can someone explain why there's this note at the trafo specs : "not for burning in tubes, duty cycle limited to approx 20%". If the trafo is solid enough to power the tube then it should be solid enough to let the tube like this a few hour, isn't it ? I might be missing something here.
Thanx in advance for your help, and for sharing this great project !
Best regards.
Eric

[mole42uk]

Hi Eric,
There's a "Search this thread" bar at the top of each thread window - on the right next to the Rating stars.

The transformer will warm up if running at full power for a long time. The 'Sussex' is a valve tester, not a burn-in tool. Ed Dinning will be able to expand on this answer.

As far as the anode voltage is concerned, I doubt it is high enough for valves like the 6550 but you could try and let us know!

[n_r_muir]

Hi,

The transformer for the Sussex valve tested is only rated for intermittent use i.e. adequate for the few minutes or so that it normally takes to test a valve. Similarly the maximum available anode voltage is set by the transformer.

The Sussex was intended to test small signal valves and is just not suited to soak testing of high power valves.

[Ed_Dinning]

Hi Eric, the transformer was designed with an intermittent duty cycle in mind as a means of keeping the cost down. A transformer to allow soak tests over a long period would be at least twice the size (and cost). The heatsinking of the power supply regulators would also need to be increased

For a similar reason I did not add heater windings to cover the multitude of voltages and currents that are used on the full range of valves that could be encountered.

In terms of higher voltages for the valves you would like to test, you may again need to look at the Sussex regulator circuits, as well as the switching, as it may not be suitable for these higher voltages.

Feel free to mail me if you need to discuss any of these points.

Ed

[ricothebrol]

Hi,

Thanks for your answers !

Then what about increasing the power rating of the circuit ? I'll order a custum made trafo anyway (I have already some trafos I have to order there so I'll buy this one in a row).

I'm not that interested in burning in tubes one by one (but still interested in understanding things), but I often need to test high power tubes like 6550 or KT88.

So I'll think about modding the circuit :
- increase the voltage and current capabilities of the trafo
- find some transistors that can replace the MPSA92, BUZ80/IRF830, MPSA42
- deport them outside the PCB and stick them on huge radiators
- use higher voltage rating caps in the B+/screen circuit
- replace the ZD1-7 zeners to get 550-600V at the HV regulator
- check if the available BIAS voltage is low enough for those power tubes
- check if the heater current capacity is high enough
- etc.

That'll take quite a lot of time

I'll come back here with a mod proposal, to get some opinions and share it, because I think I'm not the only guitar amp tech interested in that circuit !

To be continued.

Best regards.

Eric

[Little City]

Originally Posted by Ed_Dinning

Hi Folks, Sussex transformers are still available and are wound to order. PM me if you need one and I'll get it wound on my return.

Hi, fellow Ed,

I'm very interested in attempting this build. Just trying to cost it out. Are these still available? And, if so: how much does it cost to get one wound?

Thanks, Ed (Little City Repairs).

Originally Posted by G8UWM-MildMartin

I still have (28) PCBs for sale at cost (8.12 GBP).
Plus, maybe, the cost of a padded envelope, depending on whether any suitable used ones are being thrown away at work, plus the ever-increasing Royal Mail postage cost, minus the discount from using the franking machine at work, plus any applicable curency transfer or exchange fees.

Hi, Martin,

I'm very interested in trying this as a project. Are these PCB's still available?

Thanks, Ed (Little City Repairs)

[ricothebrol]

Hi,

I finally drawed my own modded version of the Sussex. I increased the current capacity, but didn't increase the voltage supply, mainly for switching reasons : it's very hard to find switches and relays that stand voltages up to 600VDC...

I chose to couple the sussex with another very nice project, that competes it very well : the uTracer. I'll put those two in a same box.

So here are the main mod :

- Oscillator replaced by an XR2206, more stable and easer to change the frequency. I added a switch to do so, as I think it can be interresting to have a rough check of the frequency response. XR2206 is now out of production, but can be easily found on evilbay for a few euros.

- The leakage test is extended to all electrodes against all the others (the tested electrode connected to the leakage test circuit, all the others are grounded)

- Anode current increased to 150mA, with a switchable 30mA limit as a security for small tubes

- Mosfet replaced by a bigger, most of all, with lower case-to-sink thermal resistance, like Vishay Siliconix IRFP460 (Farnell), coupled with a big heatsink, like this one for example :
http://be.farnell.com/fischer-elektr...c-w/dp/4621980
The max thermal resistance is : (150-35)/(300*0.150) = 2,56°C/W, and with this transistor/heatsink combination we are at 1,14°C/W.

- I also wanted to replace all the wires with Molex 0.1" connectors, for easier build and maintenance. Those can still be replaced with regular wires.

- I added one extra meter for the anode or screen voltage (switchable), to make sure the current limiter isn't lowering the voltage during the mearurement.

There are 2 boards : one main board with all functions, and one board for the rectifiers, PSU filter caps and XR2206 circuit. This choice was made to keep the ircuit on a standard 100x160mm board, and to be able to keep those noisy circuits away. The Anode and screen volate switches are shown "routed" for esthetics purposes, but the resistors are best soldered directly to the switches.

The "classic" Sussex mains transformer can be used, but then the current limit will be 100mA, and 24V and 6V trafos must be added. I will order my trafo here :
http://www.audiophonics.fr/fr/electr...es-p-3675.html
I've already ordered some there, those are good and pretty cheap. I'll post the specs after testing the circuit.

Here are the files :
https://drive.google.com/file/d/0B6K...ew?usp=sharing
https://drive.google.com/file/d/0B6K...ew?usp=sharing

I don't give the copper layout for now, I'll build it first to make sure there are no errors.

Any comments and opinions will be very appreciated !

Best regards.

Eric

[Ed_Dinning]

Hi Gents, a larger current transformer could be provided offer this design, it will of course be larger and more expensive.
A larger transformer may also be able to accommodate additional heater windings and the additional supply for another meter.

Ed

[ricothebrol]

Thanx for the info, Ed !
Best regards.
Eric

[brianf7408]

I have finally finished my Sussex build and you guys have done a wonderful job with the documentation. The Manual made life so much easier by having all the information - theory, BOM, Schematic in one place. Well done.

Now that I have it built I have a few questions I need some clarification on. I went back and re-read the manual and the entire 60 pages of this thread but still am not clear.

- What is the process for testing rectifiers such as a GZ34? I assume I set the correct heater voltage, set the anode and screen voltages to 0, set to D1/D2, set to TEST and I should get a reading of 5ma anode current... pressing the 50ma diode button I should get a reading of something near 50 ma? I am a bit confused as you can probably tell. I have tested several different rectifiers and never get past 4 ma even with the 50 ma button pressed. Before I go troubleshooting I thought I should get the process confirmed.

- This exact question was asked in post 1042 but never answered, is the Gas Test done in the TEST position? I ask because in the commissioning steps it is done in the Leakage 1 position if you follow the steps.

- Finally, I notice in many of the photos of completed testers the Grid Voltage meter shows a '-' sign in front of the voltage reading which makes sense since the grid voltage is negative. My Grid meter does not. However, if you look at figure 13 in the manual, it shows the connection of the positive lead of the meter to the positive side of the 45v supply - which of course will NOT result in a negative reading on the meter as in my case. I know this is not a big deal but for some reason I am having difficulty with this negative supply concept as I initially wired LED's 2 and 4 in backwards so if someone could just confirm that so I don't have to worry that I have messed something else up.

Aside form those questions, I have been testing a bunch of tubes I have in my collection and the results are well within expectations. This was a really fun project.

[KeithsTV]

I can't answer your GZ34 question but the Gas test is done in the test position.

As to the Grid Voltage meter reading it is a matter of personal preference whether the meter reads positive or negative. Connecting it as shown in figure 13 it will display a positive reading. Reversing the input connections to the meter will show a negative reading. It won't affect the voltage at the grid.

Keith

[brianf7408]

Thanks Keith. That may sound like a complete novice question but my thought process was...I built the unit per the schema, but everyone else's meter shows a neg sign....did i miss something? But you've cleared that up.

I still am not sure how to test a rectifier so if anyone cares to chime in, it would be appreciated.

Brian

[Top Cap]

Brian, the diode & rectifier tests were added later even though a lot of testers do not cater for these tests as it is often considered as being not reliable enough. I put the circuitry in so that I could at least get some idea of the workings of a diode/rectifier rather than none at all. For small signal diodes like the EB91, the pin switch positions would be 192310800 with 6.3V heaters selected and the Anode Voltage set to 50V. This 50V setting was added to the original Anode voltage selector switch specifically for testing small diodes. You must use D1 and D2 on the Electrode Selector switch as this brings in the lower mA current limit circuitry, the EB91 is rated for 9mA. The Sussex circuitry will be limiting this current to 5mA which should be sufficient to prove the diode is actually working. When testing a Rectifier, say the UU9 with a switch setting of 290008130, You could set the Anode voltage to the same 50V and of course use D1 and/or D2 to provide current limiting for the tests. However the UU9 has a maximum anode current of 30mA so whilst testing this valve, briefly press the 50mA button and check that 30mA is reached. If not then advance the Anode Voltage a step at a time to see if 30mA can be achieved. These measurements should be taken briefly. Diodes do not have a grid to control Anode current which is why it is important to use D1 and/or D2 which will bring in the required current limiting. Only Anode voltages are required as this circuit is used for D1 and D2, the Screen voltages can be left at zero.

[brianf7408]

Thanks Top Cap. I understand now.

[Ramonthebiker]

It's been quite some time since anyone commented on this - I would like to build the Homebrew Valve Tester - is it still possible to obtain the parts specified? Particularly the PCB and transformer?
Thanks, Ramon

[Ed_Dinning]

Hi Ramon, yes I still do the transformers and I believe one of the other forum members had some more PCB's run off a while ago.

Email me through the PM system and I'll give you full details.

Ed

[Goldentone]

Hi Ed

I am interested in the transformer and the PCB.

Could you please give me some costs on both or who I need to talk to regarding these parts.

Regards

Mark

[Ed_Dinning]

Hi Mark, you have a PM.
Can any members highlight who has the PCB's these days please?

Ed

[G8UWM-MildMartin]

I have 2 tinned and one untinned (both types with holes pierced about 0.8mm) to Mike Rowe's original design left. Prices £8.12 or £7.40 plus post, respectively.
These are from the second batch of 30.
I might order a few more (maybe 10) unless anyone has an alternative to offer (please!), but I don't think current sales would justify ordering enough to get a decent price break.
Best regards,
Martin.

[Ed_Dinning]

Hi Gents, I now have some more transformers wound for those who have been asking for them recently.
PM or e-mail me for more details.

Thanks, Ed