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Old 18th Aug 2017, 8:54 am   #101
David Simpson
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Default Re: Free Standardised Valves

Folks, I've now lost track of who has which valve. This is inevitable, and not a worry, seeing as I recommended folk to just contact each other by PM.
There is no time limit on using the valves, as long as inaccuracies highlighted are able to be remedied.
Another recap :- 6AU5GT's nos. 1 & 2 should be in circulation, as should nos. 4 & 5. No 3, which went to Dekatron in Sweden, is u/s, so is out of the loop. No 6 will head home with Mark James this weekend for him to use then pass on to others(possibly at the next Goldborne meet). Also heading down to Lancashire with him will be some 6AQ5's - again for him to pass on.
Hopefully, Dekatron will be sending me a couple of 6AU5GT's, which he has tested on his Roetest & 163. I'll have a graphing session with them, then they(nos. 7 & 8), too will be released into the fray. The 6AQ5's will be given the suffix a), b), c) etc., to avoid confusion.
Please, please post pictures of your results, added to my graphs - just for info. Especially if you add 'before & after' recalibration. Then tell us what needed doing. Once again, I reiterate - don't be shy - this isn't some public toilet where you don't want some big fella next to you to get a glimpse of your thingy.
If folk want to use Exel software, feel free, amongst yourselves. Me - I'm just a vintage fella(who doesn't loiter in public toilets), who built his DC Tester out of other vintage test equipment, and who draws up graphs in a vintage manner.

Regards, David
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Old 18th Aug 2017, 4:55 pm   #102
David Simpson
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Default Re: Free Standardised Valves

Right - three 6AQ5's have been tested & graphed, ready for Mark to take away. That's definitely it for a week or two. DIY, Windows, Garden, etc. beckon.
Keep testing, & graphing please.

Regards, David
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Old 18th Aug 2017, 7:01 pm   #103
mole42uk
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Default Re: Free Standardised Valves

Here's my plot of Valve No.5 on my Sussex. The plot follows the curve, but the numbers are slightly higher throughout which might mean an adjustment error on my machine.
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Old 18th Aug 2017, 7:27 pm   #104
David Simpson
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Default Re: Free Standardised Valves

Many thanks Richard,
It'll be really interesting to other Sussex folk, when you tell us what needed doing on your Sussex to re-calibrate.

Regards, David
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Old Yesterday, 5:05 am   #105
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Default Re: Free Standardised Valves

Quote:
It'll be really interesting to other Sussex folk, when you tell us what needed doing on your Sussex to re-calibrate.
Looking at the circuit diagram, the anode current is measured across a 1Ω resistor. The resistor in the Sussex is likely to be a 'commercial' tolerance component (I don't remember buying anything special at the time), I will look and see if I can find a close tolerance component.

The other thing I want to check is the accuracy of the anode and g2 voltages since both are set using rotary switches on resistive divider networks. I'm not sure how much effect these voltages have on the Vg/Ia curve.

If those investigations don't bring the anode current measurement into line, I may have to simply add an adjuster at the measurement point to reduce the value shown on the Ia meter.
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Old Yesterday, 5:48 am   #106
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Default Re: Free Standardised Valves

David,

Just a question. When testing the 6AU5GT Nos. 1 and 5, I followed your lead and used Va=250v, Vs=150v and Vh=6.3v. The AVO book gives Va=200v for this valve and I wondered why you chose 250v.

regards, Nick
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Old Yesterday, 5:58 am   #107
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Default Re: Free Standardised Valves

This might be interesting, I used the 'book' value of 200V. I might re-test using 250 and see what happens.

I have to go to work first, though. :-(
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Old Yesterday, 8:52 am   #108
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Default Re: Free Standardised Valves

I guess the Va=250v will take your graph line further north but at least then it will be on the same anode voltage as David and me and so will be directly comparable to our readings which yours isn't at the moment with Va=200v.

regards, Nick
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Old Yesterday, 8:52 am   #109
David Simpson
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Default Re: Free Standardised Valves

Richard & Nick, I remember mentioning this choice of 250V Va back at the beginning - 'twas to obtain a steeper curve & drive the valve a bit harder. The valve is max rated a fair bit higher than 250V. Running at 60 - 70mA, it also lends itself as a substitute in the AVO VCM's manuals recommendation of a KT33c for final calibration testing.
In a Sussex is it just the Vg pot which controls Ia ?

Regards, David
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Old Yesterday, 10:55 am   #110
Fourlegsgood
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Default Re: Free Standardised Valves

David,

Thanks for the response re the 250V Va. I must have forgotten your earlier note but it is worth emphasising that we are using 250V for the 6AU5GT to ensure all plots are on the same basis.

regards. Nick
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Old Yesterday, 11:20 am   #111
mole42uk
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Default Re: Free Standardised Valves

Quote:
Originally Posted by David Simpson View Post
In a Sussex is it just the Vg pot which controls Ia ?
Yes. Mine has a 10-turn Vg pot, seems to work well.
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Old Today, 9:24 am   #112
mole42uk
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Default Re: Free Standardised Valves

An update on Valve No.5 tested on my "Sussex". After I'd adjusted the anode volts to 245 (the closest I could switch to 250) and the screen volts to 135 (again, the closest I could switch to 150) I connected my Keithley 175 DVM to check the anode current meter on the "Sussex". The DVM matched the "Sussex" Ia meter all the way.

I wonder if the deviation at the lower Vg is due to the lower Vs that I'm applying? I might run the test again with a higher Vs and see what happens.

I re-checked the valve. The graph is here:


The Exel file is here:
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Old Today, 9:42 am   #113
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Default Re: Free Standardised Valves

And this, boys and girls, is what happens when you increase the screen supply to 160V:
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