18th Sep 2017, 8:11 pm | #121 |
Octode
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Re: Free Standardised Valves
As Richard said I now have valve 5, some initial test showed up a problem with my CT160 so I am about calibrate it, I will give an update shortly.
Regards Chris Last edited by chriswood1900; 18th Sep 2017 at 8:11 pm. Reason: Typo |
19th Sep 2017, 9:55 am | #122 |
Tetrode
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Re: Free Standardised Valves
Chris
Having had Valve 5 pass through my hands I will be interested to see your additional measurements added to it's history. Nick |
19th Sep 2017, 11:45 am | #123 |
Nonode
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Re: Free Standardised Valves
It strikes me that having the same valve tested on a variety of testers is actually a more interesting excercise. So far, the first three showed remarkably similar results from testers with similar parameters but once my "Sussex" got in there, we see some results which are a little different and I think might be more educational. I'd like to see results from other "Sussex" testers, maybe some American testers as well just to see how much the characteristics of the tester influence the results.
Will we see more results out soon?
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19th Sep 2017, 2:07 pm | #124 |
Nonode
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Re: Free Standardised Valves
Once again, I'll echo Richard's request about more folk posting their graphed results. Just a knowledge sharing exercise, not a competition between different testers. We've had a DC tester, Roetest, 163's & so on, but I would like to see more Sussex. And please - some Taylor & Mullard " coloured zone" results as opposed to graphs. Also, recent posts about Hickoks has inspired my interest in these American testers. So come on, Hickok owners, please join in.
Regards, David |
22nd Sep 2017, 4:52 pm | #125 |
Octode
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Re: Free Standardised Valves
I have been having an interesting time with valve number 5 with some strange results which I have been unable to work out. I have attached the result as an Excel file plus as a PDF graph.
The Ia results have been much higher than expected and higher than Richards results which were higher than David's original standardising. I first tried the Valve in my CT 160 and got results very different from what I expected, so I did a complete Re calibration of the CT160 other DC standardised valves check out fine but Valve 5 the 6AU5GT was producing much higher results. I rechecked my CT160 and could find nothing wrong so in order to stop myself going completely round the bend set up a DC rig using PSUs feeding an Octal holder again the results with No 5 were much higher i.e. at -15 grid voltage it was drawing 25mA and at -30v it was 101mA similar to the CT160 but lower at the top end. I then put in a 6AU5GT I purchased recently and have called CW 6AU5GT No1, with this I got virtually identical results from David's original standardised results. So can anyone please explain this mystery, I can't see how the valve characteristics could change so much or am I making some mistakes somewhere! |
22nd Sep 2017, 5:20 pm | #126 |
Octode
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Re: Free Standardised Valves
chriswood1900, could it be a problem with the valve oscillating? If it oscillates the grid voltage will swing a lot and you will get higher readings in some circumstances. This will affect your DC setup too as the oscillations can occur there too, you will need ferrite beads even in a DC tester. Try with some ferrite beads and perhaps also a grid stopper resistor and see if you get the same behaviour.
In the 6AU5GT that David sent me the cathode had fallen down into the valve itself and in some cases it shorted to the grid which made for some strange readings until I spotted what had happened, so you might have to check your valve to see if you have some mechanical problem. Banging the valve in my palm made the cathode move enough so that I could make some readings that were in line with Davids.
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22nd Sep 2017, 7:08 pm | #127 |
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Re: Free Standardised Valves
Martin thanks
I checked the valve No5 with mine and the cathode has moved down about 3mm bending the tag and leaving the heater sticking out the top, will review again in a few days as I have put my rig away. I did add beads for my DC test but not a grid stopper, my valve behaved OK in the same setup. If David is happy for me to try I will try to move the cathode back up. The 1st Picture is the No5 the Second is My 6AU5GT. I suppose GE didn't design these for handling by postal services! Regards Chris |
22nd Sep 2017, 7:33 pm | #128 |
Octode
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Re: Free Standardised Valves
I do have other valves where the heater wires are sticking out of the top and they were like that when I got them and they work just fine, but on the valve from David the heater sheath had moved down under the top mica so it was swinging from side to side shorting against the grid when the valve was handled.
You can see that the sheath is below the mica sheet in the photos. Did you use the screen voltage that David used or did you use a higher or lower screen voltage, that affects the readings too as was discussed earlier in the thread. If you have a scope that is isolated (so you don't make a ground loop or short it otherwise) you could try to measure the voltages on the anode, screen and grid to see how they behave.
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22nd Sep 2017, 8:55 pm | #129 |
Octode
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Re: Free Standardised Valves
Martin
I used the same voltages as David Va 250, Vs 150, Vh 6.3. Grid -15 to -30V Regards Chris |
23rd Sep 2017, 11:32 am | #130 |
Nonode
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Re: Free Standardised Valves
Right enough Guys, it would seem that these 6AU5GT's are prone to travel sickness. No3 which I sent to Martin in Sweden, suffered electrode damage, and now No5.
Hopefully the mixture of makes of the five Martin has sent me will be OK. They are numbered Nos 72 to 76 So far I've tested just no 72 on my Mk3 & DC Tester, and achieved a jolly good closeness to Martin's RoeTest's Gm Graph(See scanned copy). The RoeTest certainly has some wonderous software graphics. Must admit - I struggled with the non square millimetric graphing. Don't forget folks - I'll get these 5 valves down to Mark James for handing out to valve tester owners at BVWS Swap Meets, if required. Martin has also kindly sent me a Zip file of the RoeTest results for all five valves. Regards, David |
23rd Sep 2017, 7:47 pm | #131 |
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Re: Free Standardised Valves
I now have this mental picture of somewhere in a bunker under UKVRR HQ, a group of re-enactment people in RAF uniforms pushing marker pucks around on a map table of Europe representing the movement of David's standardised valves.
David
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23rd Sep 2017, 8:14 pm | #132 |
Nonode
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Re: Free Standardised Valves
Right enough, back in the day, Sgt Simpson would've had a big card index system, and every valve would have had an accurate traceability. Woe betide any airman who failed to log his results.
I must be a realist though. I appreciate that not every Forum guy is as daft about valve testing as I am. And I know that many guys have other interests apart from forum involvement. As I do, in fact. Smallholding duties, & DIY cupboard building, and decoration - all take priority just now. I don't mind these st'd valves wandering hither & thither around the UK, but I would like to see more results posted. Even if it was just a mA/V reading off someone's tester. I appreciate that drawing up graphs is not everyone's cup of tea. One of my moans is about the advent of CAD back in the 70's/80's. Penmanship or draughtsmanship has probably not been taught in schools, colleges, or the military for many a year. Regards, David |
24th Sep 2017, 6:33 am | #133 |
Nonode
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Re: Free Standardised Valves
Shhhh - Official Secrets y'know.
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26th Sep 2017, 12:07 pm | #134 |
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Re: Free Standardised Valves
After Harpenden I stayed over and popped in to see another forum member who has a VCM163 and asked him to test Valve 5 for me and my valve CW 1
The AVO test criteria 200Va/150Vs/-20Vg produced a current of 80mA and a GM of 5.2. Using David's original test criteria 250Va/150Vs/it drew 100ma at a Vg of -17V. very similar to my results. On testing my 6AU5GT at 200/150/-20 it gave 41mA with a GM of 4.3 very much in line with the original No5 valve that David tested on his AVO MK3. So an interesting change still not fully understood but at least I know my testing was valid, I suppose I should send the valve back to David so he can take a look. Chris |
26th Sep 2017, 2:59 pm | #135 |
Nonode
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Re: Free Standardised Valves
Chris I suspect that if 6AU5GT No5 draws 90 odd mA at approx. -16.5 or -17V Vg, its singing to harmonics. That's 20mA or so higher than any of the rest of us have achieved with different testers & different 6AU5GT's.
Past experience with CT160's & harmonics led me, some years back, to building several ferrite beaded adaptors for IO's, B8B's, MO's, Loctals, & so on. These I also now use with my DC Tester with any O/P B/Tet or Pentode. My Mk3 never sings, but then its not working in full high slope DC conditions. CT160's, although being much a clam-shelled Mk3, "don't like it up em". Probably because they have more cramped circuitry. Regards, David Last edited by David Simpson; 26th Sep 2017 at 3:05 pm. Reason: Ad'l info |
26th Sep 2017, 7:59 pm | #136 |
Tetrode
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Re: Free Standardised Valves
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27th Sep 2017, 10:27 am | #137 |
Nonode
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Re: Free Standardised Valves
By all means Chris, send the valve back up to me. Maybe all this travelling around the UK has miss-aligned some internal electrodes & hence altered inter-electrode capacitance, thus making it prone to a parasitic oscillation & subsequent harmonics. Who knows.
In turn, I'll send you back "Dekatron's" 6AU5GT no 72 for you to try. So far its survived the trip over from Sweden, as you can see from my post back on the 23rd. My most cursed valve, parasitics-wise is a VT136(Americanised 807). The two CT160's I once owned didn't like them, and even in my DC tester they oscillated unless I used my ferrite beaded extension box & anode lead. An EL37, however, was once tested up to 117mA DC, and behaved itself. I'm sure investigations into certain O/P valves in certain valve testers, and the production of parasitic oscillations would be an interesting separate subject. I've a lovely diddy hand held frequency counter called a "Watson Super Hunter" which has a stubby BNC aerial attachment. Rated up to 1GHz. Moving it around a valve under test which is oscillating, like a wand, reveals fundamental frequencies from around 40MHz up to approx. 150MHz. But I've never investigated the phenomenon further. Just haven't had the time nor the equipment.. Perhaps someone with sophisticated frequency counters & high freq oscilloscopes might consider having a go ? Regards, David |
15th Oct 2017, 5:29 pm | #138 |
Nonode
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Re: Free Standardised Valves
Martin & Chris, I've attached a copy of Martin's 6AU5GT No 72's RoeTest Graph - with my tabulated results added from my Mk3 & DC Tester. Obviously, my tabulations are just taken over the normal range either side of the -20V Vg. Jolly close, I reckon, for a 60 year old AVO Mk3, & a DC tester made up of parts of other vintage test equipment from the 50's & 60's(which I'm guessing cost me about £150).
I'll get this valve sent off to Chris asap. Remember folks, Mark James has a couple of spare std' 6AU5GT's of mine, and I've another 4 of Martin's remaining. Regards, David |
15th Oct 2017, 7:00 pm | #139 |
Hexode
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Re: Free Standardised Valves
As David says ... I still have two 6AU5GT's for collection at Goldborne. PM me if you would like one.
Mark |
16th Oct 2017, 7:43 am | #140 |
Octode
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Re: Free Standardised Valves
Mark,
I've sent you a PM regards our Golborne meet up. John |