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Old 9th Aug 2017, 4:09 pm   #41
trh01uk
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Default Re: Free Standardised Valves

Quote:
Originally Posted by David Simpson View Post
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
David,

yes, I need to make myself a standardised CV455. I've bucket loads of those ECC81/82 types. The problem is more setting up a DC test system to make the measurements, and be sure that all the meters are accurately in cal.

I am just going to post your 6AU5 off to Nick - so thanks very much for putting that into circulation.

Richard
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Old 9th Aug 2017, 6:38 pm   #42
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Default Re: Free Standardised Valves

Belatedly, I'd like to join in this valve-tester jamboree!

David did kindly send me a characterised valve a long time ago when I'd just finished my Sussex, but it would be good to compare it now against a valve that has already been characterised by some other testers.

If anyone has finished with a valve and would care to post it on, please PM!
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Old 9th Aug 2017, 10:14 pm   #43
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Default Re: Free Standardised Valves

About 12 months ago, I sold on a few ECC8x valves. I tested them by making up a simple tester (wander leads to suit base, and 6 or 12v to suit filament) and connected then to my Telequipment CT71 curve tracer. This gave me proper DC characteristic curves.
Les.
edit. I used a digital camera to show the full family of curves.

Last edited by MotorBikeLes; 9th Aug 2017 at 10:16 pm. Reason: Additional info
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Old 10th Aug 2017, 9:59 am   #44
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Default Re: Free Standardised Valves

Thanks for your post Les. If you've digital photos of the curves, I'm sure folk would like to see them. I'm sure trh01uk - Richard would be interested.

Regards, David
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Old 10th Aug 2017, 5:20 pm   #45
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Default Re: Free Standardised Valves

Dave,

yes, I would like to see the curves. The CT71 is an impressive machine. According to its spec it can produce voltage up to 1kV, and current up to 2A - limited to a max power of 10W. Its aimed at semiconductors, but plainly is fine for lowish power valves too.

The only thing I wonder is how accurate it is - given that we are on about accuracy in this thread?

Richard
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Old 10th Aug 2017, 5:42 pm   #46
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Default Re: Free Standardised Valves

Next 6AU5GT(No4) will be off to Neil24-7, along with one of the 12 6AQ5's which he very kindly donated to the project.

So to recap :-
6AU5GT No.1 went to trh01uk(Richard), who is sending it on to Fourlegsgood (Nick)

6AU5GT No.2 went off to Bazz4CQ(Barry)

6AU5GT No.3 went over to Dekatron(Martin) in Sweden

A KTW61 went to Jeffreyabb(Jeff)

6AU5GT No4 is off to Neil24-7(Neil) shortly

6AU5GT No.5 has also been booked by Fourlegsgood(Nick), for
more in depth calibration. Then he'll pass on Nos. 1 & 5
to whoever contacts him by PM

There is just one 6AU5GT left, which I'm waiting confirmation of another Forum participant. That's it.
Lets see how this "Round - Robin" system works out for a week or two with the 6AU5GT's. I'm not wanting them returned, but nor am I wanting folk to hang on to them for long periods. All I'm doing is generating dosh for Royal Mail!
Then I've 11 6AQ5's to test over the coming weeks.

Regards, David
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Old 10th Aug 2017, 5:44 pm   #47
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Default Re: Free Standardised Valves

Whoops - forgot to attach No.4's graphs. D
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Old 10th Aug 2017, 8:12 pm   #48
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Default Re: Free Standardised Valves

Hi David
Here are the results from my AVO MkII for the KTW61 valve.
Higher but close to David's results down to a -Vg of 9, but then the difference gets progressively greater. (Nearly 10% at -2V.) Quite a tricky job to set the Grid volts pot on the MkII. - I had to change the knob on the Grid volts because the index line on the pot didn't line up to zero when turned fully anticlockwise.
I will see what I can do with my other testers before I pass the valve on.
Jeff
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Old 10th Aug 2017, 8:14 pm   #49
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Default Re: Free Standardised Valves

Sorry about that. Picture now right side up.
Jeff
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Old 10th Aug 2017, 8:33 pm   #50
David Simpson
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Default Re: Free Standardised Valves

Jeff, I reckon your Mk2 has done jolly well. I'd be happy with that. Don't forget, AVO VCM's have a 10% margin in their nominal unloaded Va
servicing manual measurements. We'll look forward to seeing your other tester's results. No rush, just hang on to it till you're completely happy with all your testers, then pass it on if someone PM's you.

Regards, David
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Old 10th Aug 2017, 11:17 pm   #51
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Default Re: Free Standardised Valves

David, here are
(a) my notes (aide memoire for future testing) which I prepared at the time (Jan 2015, how time flies) and to be honest I would need to read them along with the CT71 manual to be sure it all makes sense.
(b) photo of the CT71 displaying test result, I think the correct one.
(c) Test equipment. Transformer in box (6V only, not 6v and 12v as I think I mentioned earlier). Small box contains valve base, "testing card" on top has connections for ECC88, ECC81 on obverse side, and card in foreground has ECC82 and ECC83 on its sides. The two yellow leads and one black are for 6V filament supply. The remaining 6 wires to LH and RH inputs of CT71.
Hope you can work it all out.
Cheers, Les.
ps, I will only post text now, photos need reducing first. Will follow shortly
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Old 10th Aug 2017, 11:29 pm   #52
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Default Re: Free Standardised Valves

I seems I lost all attachments. Try again.
Les
(And out of order.)
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Old 11th Aug 2017, 12:27 pm   #53
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Default Re: Free Standardised Valves

Les, a great set up. As you say - ideal for the ECC types. Did you strap the two internal triode halves together ?
"Dekatron" raised the question of the suitability of supplying St'd valves with either AC or DC heater voltages. Both the AVO CT160 & the Mk3's Manuals just say "L.T. Supply" on the diagram, then later say "The heater supply for the valve may be ac or dc". Me - I've always used DC, spot-on 6.3V.
AVO also say for a St'd ECC82(CV491) to draw 16mA, strapped as a single triode, when the VDM quotes 10.5mA per triode half. Obviously, AVO VCM's can obtain the Anode strapping together conditions via the top wee socket(for top cap connections) board's A1 & A2,(Pins 5 & 1). Or alter the Thumbwheel Switch code. Obviously Taylor & Mullard owners would need a totally different procedure.
Frankly, all this could be done with a decent old 6C5 or similar big single Triode. But they're getting rather rare & expensive these days for a good one. Saves all this fannying about with "Strapping together".
However, & its a big however, almost any amplifying valve could be "Standardised" on a DC Tester. Hence my choice of a 6AU5GT Pentode. I had a handful, & there are plenty of them(or similar) about still.
As I've said, hopefully in the future, some fancy curve tracing software could give a super-duper family of all the curves, mine & everyone else's, which will identify ideal standard curves with an acceptable % margin, before folk need to get their Testers & VCM's calibrated.
Hopefully, once this round-robin project has been on the go for a wee while, it will attract Sussex, Hickok, Taylor, Mullard, etc. owners to participate.
Les - if you want some spare ECC88's - PM me.

Regards, David
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Old 11th Aug 2017, 5:55 pm   #54
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Default Re: Free Standardised Valves

Right, 6AU5GT No 5 is ready to enter the fray. Will go off to "Fourlegsgood" (Nick). Hopefully tomorrow.
That leaves, lastly, 6AU5GT No 6 - which will head off to Chorley in Lancashire, when "Mark James" pops up for a visit next weekend. That's it.

Regards, David
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Old 11th Aug 2017, 6:46 pm   #55
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Default Re: Free Standardised Valves

If anyone would like to send a valve on to try out my Sussex, I'd be happy.
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Old 11th Aug 2017, 8:32 pm   #56
David Simpson
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Richard - just contact by PM - one of the other 6AU5GT participants, and arrange Postage, after they've finished with their valve. Then someone can contact you - and so on. I'm sure we're all waiting to see what a Sussex throws up - Ia/Gm/Graph - wise.
Hey there Hickok owners - come on - give it a try. Or perhaps there is an owner of one of those big Russian testers willing to give it a go, please.

Regards, David
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Old 11th Aug 2017, 9:53 pm   #57
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Default Re: Free Standardised Valves

David, in the photo showing the screen you will see a three position toggle switch just below the position knob. It is pointing to RHS. one half of triode is connected there, the other half on the other side, so switching to LHS tests the second half.
In the white box is a TQ D52 mains transformer from which the 6.3V AC heater supply is derived. It has an HT winding which, if I recall, gave 146v for HT, or could be doubled with 100UFD caps and selenium rod diodes. In my mind that could have been available for a screen supply if I moved onto pentodes.
I always had a VCM (Avo Mk2, Mk 3 then Mk 4) the last of which I sold rather too cheaply about 4 years ago. Should perhaps have kept it. 30-35 years ago, I repaired and sold quite a few valved TQ scopes, so I tested all valves to help prevent bouncers.
I read here about very low emission valves still performing well in old radios, but I found Ia and Gm really did matter in the front end of some scopes. The first little TQ scopes used ECF804, then with a redesign, ECC88s. With the earlier ones, selection was important, anything a bit low could move into the timebase. I later bought a large batch of E88CCs, so I could reject anything a bit low, and sell off cheaply as tested at R.rallies.
The recent exercise was because I had a few ECC8x valves I wished to sell. I have a folder containing 16 screen shots, so I assume I sold all the good valves. There were quite a few with quite low emissions, so I probably still have those somewhere.
I am sure if I had the need or inclination, I could do a lot with the CT71 and my little white box, but too busy with my JCB in bits right now to even think of it.
Les.

Last edited by MotorBikeLes; 11th Aug 2017 at 9:55 pm. Reason: Correct errors
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Old 11th Aug 2017, 10:17 pm   #58
David Simpson
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Default Re: Free Standardised Valves

Hello again Les,
Right enough, you should've held on to one of your AVO VCM's. They're worth an arm & a leg these days. Mind you those Tel. CT71's are jolly expensive now, and the later generation ones are going for thousands, such as the Agilent.
Me - I'll just continue with vintage interests, and a DC valve tester built with parts from other redundant vintage test equipment.
A JCB eh ? Lucky you. Pity you couldn't drive it up here. I've always wanted one, but will just have to make do with my small Yanmar 4WD tractor & its front loader.

Regards, David
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Old 12th Aug 2017, 2:24 pm   #59
David Simpson
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Default Re: Free Standardised Valves

Calling anyone called "Lee Sanderson" who has sent me a "myHermes" courier postage label. Are they wanting a valve ?

Regards, David
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Old 12th Aug 2017, 3:12 pm   #60
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Default Re: Free Standardised Valves

I received 6AU5GT (nr 1) today from Richard (trh01UK).

The lawn cutting can wait so I got stuck into doing a set of measurements after just checking the calibration of my VCM163 against the AVO manual. Luckily nothing had changed after my last calibration.

My figures are pretty much the same as David's DC tester and are shown on the attached pdf in red.

I will now send 6AU5GT (nr 1) back to Richard as I think he wants to run the tests again after having a fiddle with his tester.

Nick
6AU5GT (No 1) Fourlegsgood.pdf
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