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Old 13th Mar 2010, 10:29 pm   #221
Guitarist28
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Andy,
Looks very good - great job.

Rob
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Old 13th Mar 2010, 11:19 pm   #222
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Default Re: The "Sussex" Homebrew Valve Tester.

Thanks Rob.

I'm happy to release the .fpd files for anyone using front panel designer although it's looking like about €275 at the moment for schaeffer-ag to make and etch the complete case (using housing profile 1, inc front, back, top, bottom and side panels and fixing kit).

See http://www.schaeffer-ag.de/index.php?id=75&L=1 for the free design software.


Andy
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Old 14th Mar 2010, 5:16 pm   #223
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Default Re: The "Sussex" Homebrew Valve Tester.

Where I have to connect D1 and D2, pin switch 8 and 9? I think, they are needed when testing diodes??

Vesa
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Old 14th Mar 2010, 6:41 pm   #224
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Default Re: The "Sussex" Homebrew Valve Tester.

vesa,

I believe this feature is for future development
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Old 14th Mar 2010, 10:31 pm   #225
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Default Re: The "Sussex" Homebrew Valve Tester.

Vesa & Andy.
There is no provision for testing diodes and rectifiers on the Sussex.
When doing some research during the design stage, it appeared to me that to include this test would inordinately increase the switching complexity to the point where readily available switches could not be used. I may of course overlooked an easy solution, if anyone else wants to go down this path they are welcome to carry out any improvements and share their ideas with the forum.
My experience with AVO testers shows that they tend to test rectifiers with about 100v. Talking to a couple of friends who are Audio repair specialists and designers came up with the opinions that whilst rectifiers work perfectly with 100v, when subjected to the 3-400v normal in amplifiers, many flash over. With this in mind, I then stopped, and decided that rectifiers wouldn't be given a real test without designing a specific rectifier tester.
Mike
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Old 16th Mar 2010, 12:07 am   #226
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Default Re: The "Sussex" Homebrew Valve Tester.

One idea I have is to make a simple current limiter set to give 5mA (small diodes) but with a push button switch that increases the current to 50mA (power rectifiers). The A1/A2 switch would be a 3 Pole 4 Way for selecting A1,A2,D1 and D2. The first pole removes screen voltage when set to D1 and D2. The second pole connects the metered anode supply to either A1, A2 or to the special current limiter in the D1 and D2 positions. The third pole selects D1 or D2 as the output for the current limiter but is open circuit in the A1 and A2 positions. The Anode mA meter would provide indication of the rectifier or diode current. The 50mA test would have to be of short duration unless the pass transistor was given an adequate heat sink.
I had also considered fitting a 'Push to Test' switch in the TEST relay line so that all HT was removed until everything was set-up and ready to go, especially when switching the A1,A2,D1 and D2 selector switch. However, if you remember to set the Function switch away from TEST during switching then this will be OK.

One query, this and the original design shows screen supply to be available in both A1 and A2 positions. This means that while testing for example a triode/pentode, you could finish up with the pentode half losing its anode supply leaving the screen to take all the current while you are testing the triode half i.e. A2. You could of course open circuit the screen supply when in the A2 position, assuming the pin switch settings given by AVO would, in our example valve, place the Pentode in the A1 position and the Triode in A2.
Of course testing a double pentode would then be a problem or am I missing something here with the overall perceived problem?
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Old 16th Mar 2010, 9:28 am   #227
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi,
Thanks for the suggestion, will look into it. What do other members think?
Regarding testing dual valves,if you are testing for rxample an ECL82, the AVO book shows that when testing the triode, no screen voltage is given, I always set G2 to 0V, so the screen dissipation problem doesnt arise.
Regarding double pentodes, I agree this could be a problem, but in all my years testing valves, the only one I came across was the ELL80, and they're as rare as hens teeth so I dont really feel too worried about it.
Any other members to improve the Sussex are very welcome. This is what the forum is so good at.

Regards

Mike
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Old 16th Mar 2010, 2:04 pm   #228
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Top Cap/Swordholder,
This addition sounds good - how much modification would this mean to the current design/layout though?

Regards

Rob
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Old 16th Mar 2010, 2:35 pm   #229
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Mike
My understanding of the AVO book is the same as yours and I would leave the screen control at 0V when testing triode sections..

Les
Why not use the current pass transistor (TR2) and use a switch to change the value of R6 and R7 to control the current limit.

Frank
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Old 16th Mar 2010, 3:22 pm   #230
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Frank, yes I thought of doing this and it would work OK. I went for a dedicated low current supply so that accidental zapping of a signal diode with something around 100mA could be avoided. So I think it would be mandatory to have the switching done when D1/D2 are selected and warms me once again to the idea of having a separate TEST switch, with the present one on the Function switch acting as a safety interlock. I am now thinking along the lines of one of those miniature toggle switches which is biased one way or permanently the other with centre OFF. This would allow a quick tentative HT ON Test or alternatively turned on permanent for soak testing. Call me a coward but I like the idea of HT OFF whilst switching the electrodes about
Les
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Old 16th Mar 2010, 4:51 pm   #231
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by Andymic View Post
See http://www.schaeffer-ag.de/index.php?id=75&L=1 for the free design software.
Thanks for the info Andy
I might be able to use that program to do the front panels for my KW77 receivers.
Andy
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Old 16th Mar 2010, 5:22 pm   #232
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Default Re: The "Sussex" Homebrew Valve Tester.

You're welcome


Last edited by Dave Moll; 16th Mar 2010 at 5:59 pm. Reason: unnecessary quote of preceding post removed
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Old 16th Mar 2010, 6:36 pm   #233
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Default Re: The "Sussex" Homebrew Valve Tester.

Good points Les
I was thinking of trying to mimicking the way the VCM Mk IV tests diodes and rectifiers so as I could get an indication from the AVO book of what they should read.
This will require switching of the current limit and anode voltage, which as Mike has pointed out will complicate the switching greatly.

Frank
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Old 16th Mar 2010, 11:31 pm   #234
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Frank, well the anode volts switch will certainly give voltage selection control for the diode voltage. I find that many diodes, even though shown in the data books as operating with just a few mA's can actually handle quite a bit more in their maximum ratings. I just chose 5mA as a reasonable figure for most and good enough for example to reveal an open circuit connection to the anode. Power rectifiers are more likely to go low on emission I think due to the heavier work they constantly do.
So I just wanted the extra facility to be able to shove a lot more through them though I do heed Mike's warning about the effectiveness of testing HV diodes.

I think the biggest confusion I have suffered from is the two valves in one envelope situation and how AVO testers handle them. I was under the impression that an A1/A2 switch allowed you to select for example, in an ECL82, either Pentode or Triode with ease. I now realise I may have understood it wrong and that the A1/A2 switch should be used mostly for switching between Triodes in something like an ECC83.
In the case of the ECL82, I guess that each half is tested separately in the A1 position, setting the voltage controls as required and so the problem of screen voltage is taken care of in the settings rather than switching.
I am perhaps straying away a little from the AVO technique in trying to do both halves of an ECL82 using A1 for the Pentode half and A2 for the Triode. Its been well over 40 years since I used a valve tester and I had formed this crazy belief that the A1/A2 switch was for this function.
I need to have another read of the AVO instructions and LEARN! .
Les
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Old 16th Mar 2010, 11:58 pm   #235
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Default Re: The "Sussex" Homebrew Valve Tester.

Guys,

I've just found a problem with the BOM during construction.
The 6n8 caps (C4, C5 & C6) are too fat!!!!
I'll have a look for something more suitable
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Old 17th Mar 2010, 12:10 am   #236
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by Top Cap View Post
I was under the impression that an A1/A2 switch allowed you to select for example, in an ECL82, either Pentode or Triode with ease.
Hi Les
I think you're right in saying this. I have an older Taylor valve tester it wont test the more modern valves. If I remember right it's a 47A.

To test a dual valve in it there is two sets of settings of the selector switches given in the valve data for that valve, one for each side of the valve. Apart from the heater setting you have to set up the tester from the start to test each side.

My understanding of the AVO is that the selectors are set at the beginning and the second half of the valve can be tested just by moving the switch from A1 to A2 and resetting the anode, screen and grid voltages.

An emission test is the most thing that I would be interested in for rectifiers. For testing such ones as PZ30's where one half can have a much harder life than the other.

Frank
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Old 17th Mar 2010, 12:37 am   #237
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Default

Top Cap,

Your layout shows incorrect polarity for TR8

It should be B C E from top down, so you've transposed B & C.

Odd orientation that MJE 350 but it checks with the Circuit Diagram

Andy
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Old 17th Mar 2010, 12:54 am   #238
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Default Re: The "Sussex" Homebrew Valve Tester.

Mike,

A couple of questions if you don't mind....

How critical are TR6 & TR7?
I have about 150 BC307A's. The difference appears to be hfe. Iv'e tested a batch and have consistently about 175 to 180 hfe. Will these be OK?

Also, C4, C5 & C6. Is 10n okay instead of 6n8?

Regards

Andy
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Old 17th Mar 2010, 8:48 am   #239
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Default Re: The "Sussex" Homebrew Valve Tester.

Andy,
The BC307's should be OK, adjust VR1 for consistant and lowest distortion oscillation.
10n will lower the frequency, but I don't see any problems with that. Try 4n7 as well, as it will raise the frequency further away from the mains frquency which may be beneficial.
Either way I dont think it will be critical.

Mike
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Old 17th Mar 2010, 1:05 pm   #240
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Andy (Andymic)
The BOM appears to have an error and I am unable to view it anymore. Is it me or is there an error in the viewer?

Thanks

Rob
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