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Old 4th Aug 2017, 9:58 pm   #21
David Simpson
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Default Re: Free Standardised Valves

6AU5GT Valve No3 has now been tested & graphed, and will be mailed off to "Dekatron" in Sweden. Hopefully he'll post results on the Forum, and no doubt contribute some technical advice.
More folk are asking for a st'd valve, so I'm hoping that someone will find some surplus ones in a gash box.

Regards, David
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Old 5th Aug 2017, 7:39 pm   #22
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Default Re: Free Standardised Valves

I received the valve from David this morning and have tested it on my VCM163 (Va 250, Vs 150V). All of the data now available for this valve is shown (I think) in the the attached figure.

This shows;
> David's original data measured by hand
> My data, obtained by twiddling the Vg knob on my 163
> My data, taking the Gm from the Gm meter with Vg set at -20V.

As you can see, the Gm's "range" from 4.7 to 4.8. For Ia, I'm reading about 4% higher than David's hand data. Seems quite good I think .

B
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Old 5th Aug 2017, 8:32 pm   #23
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Default Re: Free Standardised Valves

That's great Bazz. I like the software produced graph. Any chance that you could do a quick hand graph superimposed on my original A4. It'll keep us old fashioned folk on track when comparing results meantime.
Someone else has also proposed software results, but with a different program - might be a bit confusing. However, plaudits to all software aware folk. Perhaps as this project progresses or comes to an end sometime, then hopefully someone will volunteer to correlate all the results in a "flip-over" software format. Not to show who is "King of the Castle", but to set a benchmark that all us valve tester & VCM folk can aspire to.
To continue - Jeffreyabb has also asked for a st'd valve, but I've run out of 6AU5GT's for a few days. So will send him a Osram KTW63 meantime. See attached graph results.

Regards, David
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Old 6th Aug 2017, 1:12 am   #24
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Default Re: Free Standardised Valves

David, attached is an updated version of your original datasheet for SNo.2, with my 5 points added for comparison. May not be perfectly accurate as the printed graphing lines on the copy I was working from were almost invisible, so I was struggling a bit.

B
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Old 6th Aug 2017, 10:07 am   #25
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Default Re: Free Standardised Valves

Thanks Bazz. Did you not fancy plotting the full tabulation ? Bit of fannying about I know, but I'd like to see the whole torso, knobbly knees & all. Valves do exhibit "kinks", some slight, some larger, over the characteristic curve. I actually avoid "averaging" them out graph-wise, hence the reason for my resultant exponential curves being made up of linear tabulated plots.
Your software produced graph actually almost follows the mathematics of the curve, similar to the design spec used by AVO engineers back in the 50's. My basic graph just gives an approximate DIa/Dvg(Delta Ia/Delta Vg), say - between -19V & -21V. Whearas your plot is closer to the much smaller delta Ia/delta Vg which, for instance, the CT160 exhibits when RV1((Ia/Vg Dialled pot) is wound up. Actually, if folk want to use "Zoom" on their computer, they could almost get the centimetric A4 graphing down to millimetric for an accurate dIa/dVg.
Delving into the maths of exponential curves,using calculus, to determine the profile of the curve in terms of x squared, I'll leave to others.
I've just used a basic graph for all to follow, but its great if enhanced software can be added by others.
If I could get someone to come and mow nearly an acre of grass every week or ten days, pick bucket loads of soft fruit, heaps of weeding, sacks of tatties to dig out, bush & tree pruning, Labrador gundog training - - - I could spend hours every day at my drawing board & computer. "Poke that" as the actress said to the bishop.

Regards, - a weary David
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Old 6th Aug 2017, 3:48 pm   #26
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Default Re: Free Standardised Valves

Hi David, yes I can do the full plot if that's of interest.

Here, I am (as ever) "working towards" putting the house on the market, which can consume every minute. The endless stash of ham radio junk and car-related junk fits badly in to the dream-home pictures which estate agents want to put on the net; maybe I could put some of it under the floorboards .

B
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Old 6th Aug 2017, 8:54 pm   #27
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Default Re: Free Standardised Valves

Hi, David,

here are the results of the 6AU5 No.1 from my AVO VCM Mk.IV. I have to say its somewhat disappointing - and perhaps puzzling too. It shows my VCM is now quite out of cal at the lower values of Vg, between about -30 and -17V. Strangely the error drops dramatically above -17V, getting to agree well with your Mk.III.

Again, strangely, the gm value is pretty close to what you measured on your DC test set up.

My VCM was thoroughly gone through to weed out all out of tolerance resistors, check transformers and adjust cal about 4 - 5 years ago. Its possible I suppose that some resistors have subsequently drifted out of tolerance since then (I only replaced the out of tolerance ones). I will need to go through the process again I think.

Richard
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Old 6th Aug 2017, 8:58 pm   #28
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Default Re: Free Standardised Valves

Sorry, I had to re-optimise the PDF file before I could upload it to the forum - here it is.

Richard
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Old 7th Aug 2017, 4:27 pm   #29
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Default Re: Free Standardised Valves

Can I ask whether the valves are being sent back to David after use or are they available to be sent on in a sort or 'round robin' fashion. If the latter I would be interested in paying for someone to send on to me to try in my VCM163.

Nick
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Old 7th Aug 2017, 5:09 pm   #30
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Default Re: Free Standardised Valves

Nick - Round Robin -Once I've posted them initially, I'm not wanting them back. Give it a couple of weeks or so - then get in touch with one of the first few participants who lives nearest to you, or is likely to be attending a mutual BVWS swapmeet. As long as folk post their graphed results - on an original graph(6AU5GT No1, No2, No3 - & so on), I'll be happy.
Richard, your graph looks not bad. Only start swopping high spec calibration resistors as a last resort. Might just be something simple such as a dial on a pot shaft loose or requires a wee alteration.

Regards, David
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Old 7th Aug 2017, 7:51 pm   #31
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Default Re: Free Standardised Valves

David,

Thanks,

Nick
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Old 7th Aug 2017, 8:50 pm   #32
David Simpson
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Default Re: Free Standardised Valves

Just a reminder, folks - if anyone just has a non AVO tester which doesn't indicate changes of Ia, please just post a picture of your GOOD/ REPLACE or GREEN/ RED meter indications. They are just as important.

Regards, David
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Old 8th Aug 2017, 6:11 pm   #33
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Default Re: Free Standardised Valves

Right folk, I've now three other free 6AU5GT valves to standardise & graph. But I think that's it. I've had a kind offer of some similar "beam pentodes" and might use them if the demand is there.
If Nick or one or two other folk want a 6AU5GT just get in touch. But now that valves are in circulation, future prospective folk should contact the original participants who could pass the valves on after a few weeks adjusting/calibrating, if necessary, their testers & VCM's.

Regards, David
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Old 8th Aug 2017, 9:11 pm   #34
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Default Re: Free Standardised Valves

David, I will PM you.

regards, Nick.
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Old 9th Aug 2017, 10:48 am   #35
David Simpson
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Default Re: Free Standardised Valves

Well, I reckon that's just about the 6AU5's all bewked. Six in all, plus one KTW61.
As I said in my last post on Monday - - A simple picture of your meter indication would do for non - AVO testers/VCM's, where Ia cannot be read of &/or tabulated for a graph.
I've attached an idealised display of a 6AU5GT, and would expect just about all tester's meters to be within ten mm either side of "Central Green". 5mm would be pretty spot-on. For instance those markings on my meter on the mA/V scale are approx. 5mm apart. Anything more than 10mm out, or down into the "White" or "Red" l/h zones, would require calibration &/or repair.
I keep reiterating - this isn't a "someone's willie is bigger than someone else's" project. Just a project to raise awareness amongst friendly participants & Forum members, of a general worry about just how accurate one's valve tester/VCm is. These testers are what ? - 50/60 or more years old. Many have had a hard life - such as the military versions of the CT160's. So there is no shame if an old tester is a bit out of cal. & needs some TLC.
Hopefully, if half a dozen or more of these valve float about amongst Forum folk for a year or so - one or two experience electronics guys with spot-on VCM's in different localities in the UK - will offer to recalibrate folk's machines, or have a look at them at Swapmeets. Just a thought.

Regards, David

Regards, David
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Old 9th Aug 2017, 11:10 am   #36
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Default Re: Free Standardised Valves

David,

based on the results from my own VCM Mk.IV, which I would call unacceptably inaccurate - I would say the need for checking is obvious.

Mine was restored and thoroughly checked about 4 to 5 years ago - but is now inaccurate in this specific test. Its rather rare that I test valves much below -15V for Vg, and it may be since the inaccuracy in mine appears to start below -17V I haven't noticed it to date.

If there is a flaw in your approach it is that you assume checking over one set of Va, Vs and a limited range of Vg is sufficient to find problems. I now need another standardised valve to do the Vg range 0 to -15V. I can make my own given time.


Richard
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Old 9th Aug 2017, 11:28 am   #37
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Quote:
Originally Posted by Fourlegsgood View Post
Can I ask whether the valves are being sent back to David after use or are they available to be sent on in a sort or 'round robin' fashion. If the latter I would be interested in paying for someone to send on to me to try in my VCM163.

Nick

Nick,

as you can see from tests on my VCM I need to do a certain amount of fault finding and repair. So I will need to re-run the tests at some point in the future. However that is going to take me a while, and I am very happy to pass on the 6AU5 No.1 to you for you to test yourself. When you are done with it, I may ask for it back again.

You will need to pay me the postage as I did David initially. If you want to take me up on this send me a PM.

Richard

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Old 9th Aug 2017, 12:43 pm   #38
David Simpson
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Default Re: Free Standardised Valves

Right enough, Richard you might well need a smaller valve for testing the lower ranges of your Vg pot. That's where a CV455 or CV491(or their ECC equivalents) would come in. But as I said originally - I've non available. Perhaps someone out there with a few, and a spot-on VCM, might be magnanimous enough to offer them as Standards, as I have offered 6AU5GT's.These yanky 6A*5GT range of "Beam Pentodes just seemed to me to be a robust sort of valve for folk to use.
Experience with CT160's has told me that the first quadrant winding (0 - 5V) of the Grid pot RV2's three segment winding is susceptible to cooking. But I'm sure there is heaps of info on "Search" about all the different pots in use for Vg.
If Nick & Richard come to a P & P arrangement, please let me know, and it'll free up one of these recently acquired 6AU5GT's I have left.

Regards, David
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Old 9th Aug 2017, 2:04 pm   #39
David Simpson
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Default Re: Free Standardised Valves

Folks - have a lewk at the picture :- Just arrived in the post - Twelve 6AQ5's very kindly sent, bucksheesh, by "neil24-7" ! Very generous indeed. So once all the 6AU5's of mine are out there in Forum circulation, as I'm not wanting them back, these will be used if the demand continues.

Regards, David
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Old 9th Aug 2017, 4:02 pm   #40
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Default Re: Free Standardised Valves

Quote:
Originally Posted by David Simpson View Post
If Nick & Richard come to a P & P arrangement, please let me know, and it'll free up one of these recently acquired 6AU5GT's I have left.
Regards, David
Richard is sending me his valve and then I will send it back to him so I am sorted and will add my results to that valve's graph.

Nick
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