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Old 11th Dec 2019, 6:48 pm   #1
juanafati
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Default Some help for Precision series 920 valve tester.

Hi everyone,

I have recently bought a Series 920. As an American tester, it is mainly intended to check american tubes because the charts found, and rolling data tubes in the device, list american tubes.
I found a chart with some European tube data at the end, but I have quite a few European ones which I need to test and they are not listed there. The oldest and most recent ones.
I can't find the data of the position of the controls in the tester for them.

I would be pleased if anyone can tell me the exact use of the controls lettered C and D of the tester. I mean, if they control the voltage and/or the current to the anode, how can I know the values they give in each position?
If I knew those values, I could possibly use the information of those tubes datasheets to place the controls in the correct position and, so, be able to test my European tubes with the tester.
I also suppose controls lettered E and F give the "real" position of the pin tube for the screen grid and filament respectively.

I'd be grateful for any information you can give me, so to make my purchase useful and not nearly useless as it is now.

Thanks for reading.
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Old 12th Dec 2019, 6:44 am   #2
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Default Re: Some help for Precision series 920 valve tester.

Hola, welcome to the forum. There's schematics and operating instructions here - http://oldradios.50webs.com/precision/ . If you search for Precision etc tube tester you'll get more results.
Lastly a lot of American tubes have Euro equivalent's, EG EL84 = 6BQ5, a good place to start de-coding valve numbers here - http://www.tubedata.org/

Hope that helps, Andy.
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Old 12th Dec 2019, 1:43 pm   #3
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Default Re: Some help for Precision series 920 valve tester.

Hi Andy,

Thank you for your welcome and for the first word of your message.
I already have all that information. I have read it several times (and translated the instructions into Spanish, in case anyone needs it) but I don't get a clear idea enough to try to test an unlisted tube, setting the controls with a personal accurate criteria which could give me a correct unrisky test result.
Perhaps the message should have included the question:
"Can anyone tell me how to use the tester for new or old unlisted tubes? and how can its controls be set having the tubes data-sheets as reference?"

I have not found equivalents for my old tubes (i.e. Radio-Micro, B406, B405, A410, ...) and some equivalents for others are not in the charts lists (EM84, ...). That's my problem.
I would need to get other testers and it is not worth the use I would do of them.

Thanks for your help.

NOTE: I would like to change some details on my first message. They are badly expressed. Is it possible?
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Old 12th Dec 2019, 1:59 pm   #4
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Default Re: Some help for Precision series 920 valve tester.

Quote:
Originally Posted by juanafati View Post
NOTE: I would like to change some details on my first message. They are badly expressed. Is it possible?
Sorry, but it's not possible for you to edit your post. Just post a correction in this thread.
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Old 12th Dec 2019, 3:02 pm   #5
juanafati
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Default Re: Some help for Precision series 920 valve tester.

Some corrections to my first message:

Quote:
As an American tester, it is mainly intended to check american tubes because the charts found, and rolling data tubes in the device, list american tubes.
As an American tester, the data charts I have found for it, and the roll chart in the device, list mainly American tubes.

Quote:
I mean, if they control the voltage and/or the current to the anode
I mean, if they control the voltage and/or the current to the control grid and/or screen grid.
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Old 12th Dec 2019, 3:26 pm   #6
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Default Re: Some help for Precision series 920 valve tester.

I've looked at the manual for the 920 and I think the instructions are perfectly clear with the function of each knob being defined.

You need to look at the pin out and characteristics of the valve you want to test and set the controls accordingly.

This is my favourite port of call when it comes to valve characteristics:-

http://www.r-type.org/

As an example an EL84 pentode:-

http://www.r-type.org/exhib/aaa0028.htm

The information you need is at the bottom of the page.

You can't expect to use a valve tester such as this without some knowledge of pin outs and characteristics
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Old 12th Dec 2019, 5:10 pm   #7
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Default Re: Some help for Precision series 920 valve tester.

Station X,

Thank you for the links suggested. I have not asked anything related to tubes/lamps characteristics because I do not need them, by now.

Up till now, apart from your link, I usually visit the following ones to get information for my needs -related to tubes-:
- https://www.radiomuseum.org/
- http://www.hupse.eu/radio/tubes/IndexValves.htm
- https://frank.pocnet.net/sheetsB.html
- ...and some others.
And, of course, the pages from my country for a more local or regional info.

I have dared to look for help here after having obtained and analysed as much information I could afford, about the posed message information, and which leads me to no final satisfying conclusion.

Quote:
You can't expect to use a valve tester such as this without some knowledge of pin outs and characteristics
Your last comment is, from my point of view, out of place.

Besides, I like to obtain the most from each device I have, and that is what I am looking for from this tester and that is the reason of my posted message.

In my opinion, If I can obtain what I seek, It would be of interest for quite a few of us, users of Precision 9xx Series.
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Old 12th Dec 2019, 5:16 pm   #8
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Default Re: Some help for Precision series 920 valve tester.

As Graham says you should be able to work it out by looking at a valves datasheet. All valve testers work in pretty much the same way. They will have several voltage sources inside, one or two low voltage for the heaters/filaments and control grids and one or two for the anodes/screen grids. Cathode is nearly always grounded. Next there will be either switches or a patch bay so you can send the correct voltage to the correct pins. Lastly either an AC source is sent to the control grid and/or the current is monitored and read off on a meter.

So, say you have a valve not listed for your tester, there are two ways to go about it. Either set voltages etc as in the Avo valve data manual (available as free download), see attached for the EL84. As you see its says Neg grid volts 7.3v, Anode and screen 250v, that will give you 48mA of emmision or 11.3mA/v. You could check everything is set right by using a voltmeter to probe each pin before testing. The B406 is listed in it.

Another way to set up your tester is by using a valves mutual characteristics graph, see attached for the EL84. The graph is telling us the screen is at 250v, making sure to keep to the left of the curved line which is maximum dissapation limit, look for a place where lines cross and are easily read, EG anode voltage 200v, grid volts 8v, this gives you 40mA. Hope that makes sense. You can calculate gm from the graph, as well as Ra etc, but this takes some practice.

Andy.
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Old 12th Dec 2019, 5:54 pm   #9
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Default Re: Some help for Precision series 920 valve tester.

Quote:
Originally Posted by juanafati View Post
I would be pleased if anyone can tell me the exact use of the controls lettered C and D of the tester.
That's explained in the manual from which I've posted an extract. However you'll need to read the whole manual, in particular the testing procedure, in order to understand exactly what these controls do.

I don't have one of these testers (I'm an AVO man) so I can only give you general advice based on what's in the Precision manual.

Have you tried testing valves for which the tester has settings in order to get an understanding of how the tester works?

I sometimes have to determine settings for valves which aren't in the AVO data book, but I can only do so as I've previously tested valves for which settings are available.

This will be my last contribution to this thread.
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