Amplitrex AT1000 Software Error

The Amplitrex AT1000 computer controlled tester

Amplitrex AT1000 Software Error

Postby stern71 » Sun Jan 22, 2012 11:55 pm

Hello,
my name is Heiko and I am 40 years old. 
My hobbies are tube technology, photography, travel and table tennis.  
Tube technology is my favorite.
 
To test my tubes I had decided me to buy a good tube tester. 
My dream was a Amplitrex AT-1000.  So far  the Amplitrex worked fine. 
I  tested tubes as normal ly, like  ECC81, ECC82, ECC83, E88CC, EL84 and EL34. 
The tube tester worked without problems.

Today I got from a friend a couple 6B4. 
This is a  directly heated triode, similar to a 2A3, but with 6.3 Volt heater. 
The measured values were very bad.  Since I also have some 6B4, I've also tested those. 
The result was clear:  All tubes had very poor emission values!

Then I happened to find the information on the site: www.jacmusic.com  
He had the same problem with directly heated tubes. 
It seems the Amplitrex has an  issue with the bias voltage being wrong for DHT.  
I am disappointed and hope to find help.

I use the Amplitrex currently without a computer because I have an Apple and has programmed the software for Windows only.
 
Who can help me? 
How can I eliminate the error? 
Is there a software update from Amplitrex?

 
Thank you for your help!
Heiko
stern71
 
Posts: 3
Joined: Sun Jan 22, 2012 11:52 pm

Re: Amplitrex AT1000 Software Error

Postby Admin19 » Mon Jan 23, 2012 11:06 am

Hello Heiko,

this going to be a very long answer, but it's a confusing problem we have here. Pleas take your time and read it in detail. Also you should draw on a piece of paper a Directly heated Tube (DHT) and apply the test voltages to it, with the heater connected to ground with one end. This is how the AT1000 works.

We use three Amplitrex AT1000. One here in Germany at jacmusic, one in the factory in the Czech Republic, and we have one as a spare. Let me say the spare we never needed.

A major issue is to my personal opinion the grid voltage of DHT is represented wrong by the tester. This issue is only for Directly heated tubes (DHT) and for indirectly heated tube it doesn't matter. Reason is simple: The tester's hardware by definition connects one end of the heater to ground, the other to the heater DC voltage. However, by definition the grid voltage of DHT is defined to the CENTER of the filament. This definition can not be changed. If you would do so, you get test results deviating from the real values the tube has.

Let's describe the problem by using the 6B4 tubes as you had. (This is a 2A3 version with 6.3 Volt heater). So curves and operating points are the same as with 2A3. That is: At 250V Plate, and -45V grid, a bogey tube draws 60mA. You can look this up in the 2A3 or 6B4 datasheet. (Bogey tube is a word for a tube that has exactly the data sheet values).

So this means if I have such a tube here, and I put in in a circuit with 250V, -45V, it will draw exactly 60mA. When I put that tube on a tester like Metrix U61B or Russian L3-3, or any other tester of this kind, that data will reproduce, meaning these read 60mA and nothing else. Besides we need to understand, this 60mA is not a result of a test method, it is an Inner value of that tube. This tube is 60mA, at 250V /-45V and nothing else. Any tube tester that tells you another value than 60mA is making a mistake. For instance of you test the tube with 5% too low heater voltage, you sure will not get 60mA any more, but perhaps 55mA. It would be wrong calling this a tolerance problem of the tube.

The problem with the AT1000 is the grid voltage. WIth the 6B4 tube, that we take as example here, the heater CENTER is at +3,15 Volts. (So that is half the heater voltage). Then the grid gets supplied by the tester with -45V. So the resulting voltage between grid and the heater center is -48.15 Volts, and not -45 Volts. So we are -3.15 Volts off specs. Now with the transconductance of 5.5mA/V this would roughly result in 3.15 x 5.5 = 17.3mA less plate current. So instead of 60mA you get 42,7mA only, and the tester would say this tube is at 71% only. Though in fact this is a 60mA tube and it is at 100%.

This problem gets less with tubes that have lower heater voltage. So when doing the same exercise with a 2A3 bogey tube, you would get 53mA instead of 60mA. So I think nobody ever noticed this!

To my personal understanding this is an error with the tester's software, and should not be called an alternative test method. Interesting, this test method DID excist with some of the very old tubes from the days before we had AC mains voltage, and tube equipment ran only on batteries. Some specific receiver tubes were defined with the heater grounded on one end, because that's the way you were supposed to use them. But I must say these were extremely rare tubes already by then, and all later DHT tubes were defined by the manufactorer with the heater center being the reference for the grid voltage.

The sofware correction for the AT1000 is very easy to do. Just subtract in software half the filament voltage from the grid voltage. That is only for DHT tubes of course. So if the user want to apply -45V to the grid of a 6B4, and the tester lifts up the heater center 3.15V, the tester must output -41.9V to the grid, the tube will read 60mA as it should.

I understand from Chris Terraneau (Amplitrex company owner) this is what he has is mind. Only my objection is with the way it is done. When I understand it correct, the tube test data table is adapted simply for the higher grid voltage. The first problem is the way this is displayed on the test results. So the tester is going to come up with a tube that tests 60mA at 250V -41.9V. What is right is the 60mA. What is wrong is the -41.9V. This is in reality -45V. It may appear not so bad in the stand alone mode, since users are likely focussed on the plate current adn transconductance they get, and these values are displayed correct. However the TEST CONDITIONS are now displayed with an error in the grid voltage. This gets visible more clearer when you create a printed test result. If anyone tries to verify those test results with another tester (which has no such error) he would set his tester for those conditions. If he uses -41.9V, he finds 77,3mA instead of 60mA as on the test report, and I get a complaint.

Another issue is when somebody sets up new tubes with the editor program, and also the tube curves are plotted with all grid voltages wrong. This doesn't get solved this way.

So all in all, the proposed solution is very unsatisfactory. To my understanding the only realy good way it to correct the grid voltage in software. That would remain the tube data tables unchanged too.

To have no misunderstandings, I LOVE the AT1000 for it's realiable and well thought of hardware. It is definitely worth it' price, and much recommended. Also the Email support with technical questions is just excellent. The weak point from my view is the software, which doesn't get out of this product what could be in it. I send several proposals to Chris Terraneau before which would greatly improve the User's value of the tester, but so far only one was realised. (This was the a loud clack noise with Audio output when using a headphone).

Generally I would say, we need not always a "work around" for a problem. There comes a time where the software needs a general update, and all known issues get covered. Well I hope Chris reads this :)

Jac
User avatar
Admin19
Site Admin
 
Posts: 65
Joined: Sun Dec 11, 2011 1:55 pm

Re: Amplitrex AT1000 Software Error

Postby stern71 » Mon Jan 23, 2012 10:57 pm

Good evening,
I have also sent an email Amplitrex and described the error.
Chris Terraneau responded quickly and offered the following solution.

Regards, Heiko

[i]With filamentary type tubes, the grid bias voltage should be reduced from specification, by one-half the heater voltage.
Here is the existing test setup for the 6B4:
6B4,G,D,P,250,000,0600,000,450,052,3,0,5,000,1
The grid voltage setting is the "450" which means 45.0 volts. Since the heater is 6.3V we should subtract 3.2V (rounded to nearest tenth-volt).
So the corrected test is:
6B4,G,D,P,250,000,0600,000,418,052,3,0,5,000,1
The above has changed the grid bias voltage to 41.8 volts.
Thank you for bringing this to my attention. It will be changed in the next release of tube data.
You can change it yourself, use Notepad to alter the tubedata file, and then upload the modified file using the Tubedata Editor program, supplied on CD-ROM.
This has been corrected for other filament-type tubes, such as the 300B, 2A3, etc.
[/i]
stern71
 
Posts: 3
Joined: Sun Jan 22, 2012 11:52 pm

Re: Amplitrex AT1000 Software Error

Postby Admin19 » Tue Jan 24, 2012 11:25 am

Hello Heiko,

this solution is only working for the stand alone mode. So Emission will be reported at 100% now for a bogey tube. (A bogey tube is a tube exactly at the data sheet value). So now the tube gets tested it at the "wrong" grid voltage, just to get the "right" plate current. You wouldn't see that in the "test results" display, on the tester itself.

In the PC mode however, the error will stay! The plate current is now correct, but the grid voltage is now wrong. Just make a print from a test report, and do exactly those settings as you see there, on your Neuberger 375. You will see the Amplitrex produces wrong data still. Besides the problem stays with the tube curves, all plate currents are dead wrong (or all grid voltages are wrong, depending how you want to see it). This is a real bad issue, it needs a software repair, and it can't be patched by changing the data in the file tubedata.csv
User avatar
Admin19
Site Admin
 
Posts: 65
Joined: Sun Dec 11, 2011 1:55 pm

Re: Amplitrex AT1000 Software Error

Postby stern71 » Fri Jan 27, 2012 8:28 pm

Hello,

Amplitrex answered me.
Amplitrex will seek an optimal solution for the problem to find.
Presumably there will be a software update.

I am pleased that Amplitrex has responded so quickly and trying to fix the problem quickly.

regards,
Heiko
stern71
 
Posts: 3
Joined: Sun Jan 22, 2012 11:52 pm


Return to AMPLITREX

Who is online

Users browsing this forum: No registered users and 1 guest

cron