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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 14th Aug 2017, 3:53 pm   #81
David Simpson
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Default Re: Free Standardised Valves

Nick, actually both Valve no5 & no6 exhibit quite a kink in the -20 to -15 Vg area. Both were tabulated in the late afternoons of Sat & Sun, approaching 5pm. I do recall having to monitor & adjust Vh & Va more often than normal on my DC tester set-up. No way am I making excuses, but I usually try & avoid testing near mealtimes. As the rural mains tends to fluctuate a bit. However, it just fitted in with my painting jobs this weekend. I'll repeat the tabulations on those two valves in morningtime later in the week & let you know.
I did read about it some time ago - but how exactly does the 163 measure Gm ? Doesn't it superimpose a signal of a few KHz on to the basic 50Hz grid -ve half wave pulses, then demodulate it again on the anode. I've never owned or worked on a 163.

Isn't valve testing fun? Regards, David
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Old 15th Aug 2017, 5:17 pm   #82
David Simpson
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Default Re: Free Standardised Valves

Ah - sorted - found out, I think, why Nos 5 & 6 had those kinks. Mild Parasitic Oscillation! Obviously I can only retest No6, but it went well, and a revised tabulation & a decent Gm curve was achieved. Tested the valve using my extra ferrite beaded extension box. I never expected 6AU5GT's to be bothered with P.O. And anyway, all the valve pin leads on my LMA have beads. The first three valves were fine, but the second three are a different make & valve base construction, perhaps they are more prone to P.O.
Anyway, its a lesson learnt for all of us.
The retest also included re-arranging my angle-poise fl. lamp closer to the Vg meter, to avoid the slightest parallax error.
Worth mentioning - I've always externally monitored the heater supply where it enters the DC tester with valves drawing high heater current. The O/P from the DC PSU needs to be higher than 6.3V to give 6.3V at the valve holder. Due to voltage drop over a couple of feet of cable. These valves draw over 1A. I'll need to change my 0.75mm sq. flex to 1.5 or 2.5mm sq. to be on the safe side.
Another plea to Taylor & Mullard owners - if you don't want to get drawn into all this hoo harr about graphs & Exel software, or suspect that AVO VCM owners might look down upon your tester's results - just PM me & I'll supply a St'd valve without making it public, so to speak.

Regards, David
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File Type: pdf 6AU5GT No 6(Rev)(a).pdf (635.7 KB, 9 views)
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Old 15th Aug 2017, 6:38 pm   #83
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Default Re: Free Standardised Valves

David,

I am glad you got to the bottom of it. I thought it was strange. Your DC tester and my VCM163 followed almost identical curves for Valve 1 with no kinks but there was a variation on Valve 5 and it was the DC tester curve that had a kink and so was perhaps why it was prime suspect.

Regarding the heater voltage drop, I have always wondered about this on my VCM163 because the heater voltage with no load is accurate but when the test is underway and the heater is drawing current the heater voltage can drop considerably. I noticed this when testing some 2A3 valves. My inclination was to ignore the dial setting and keep winding the heater voltage it up until I got the correct voltage under load (as measured on a MM). I did post a question in the AVO163 sticky about this but it went unanswered.

ANYWAY, I am sending 6AU5GT Nr 1 back to Richard and 6AU5GT Nr 5 is available to be sent on. Just send me a PM with your address and I will respond with a PayPal address for postage payment and then send the valve on.

Thank you again to David for initiating this fun and useful exercise.

regards, Nick
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Old 15th Aug 2017, 7:12 pm   #84
David Simpson
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Default Re: Free Standardised Valves

Thanks Nick for your participation. Hopefully another valve testing fella will get in touch with you.
Just noticed - the picture labelled "monitoring grid voltage" should read - monitoring heater voltage. By the way - it shows my NEWLEC(AVO) DMM, I love it.
On all VCM's & testers I suspect that the Heater transformer windings do load up, resulting in possibly lower than expected heater AC voltages under high heater current conditions. On AVO valve holder panels - H+ & H- can be read off the wee Top Cap connector panel, or off any unused valve holder. Remember - whatever code is set to say an IO valve holder - the same connections are made to any other 8 pin, or 9 pin, valve holder. Folks - if a B9 valve breaks down - don't throw it away - gently break the glass & remove the gubbins inside, then connect leads to all the 9 pins for connection to a banana plug socket box, or whatever. If you're making a B9 ext box - fit ferrite beads while you're at it, and fill the valve base with araldite - should last a lifetime.

Regards, David
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Old 15th Aug 2017, 8:36 pm   #85
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Default Re: Free Standardised Valves

Y' mean a bit like this one, David?

I was lucky enough to score a few B9 Cinch plugs!

Found a McMurdo octal plug as well, so an octal break-out box will be next when I get a few minutes spare. Don't know whether to scratch my watch or wind my ass at the moment...

Cheers,

Frank
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Old 15th Aug 2017, 9:29 pm   #86
David Simpson
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Default Re: Free Standardised Valves

Frank, that's just the ticket. Folks - take note how close to the pins Frank has fitted the ferrite beads. Very neat job.

Regards, David
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Old 15th Aug 2017, 10:36 pm   #87
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Default Re: Free Standardised Valves

Frank (frankmcvey), I hope the comments on your tube adapter below will help as I have had these problems myself when making tube adapters.

If you make small kink in the wire right beside the ferrite bead it will stay in place and not move around.

You can also use shrink tubing covering the bead and the tube pin plus the wire to make sure that it stays in place close to the tube pin.

One more benefit from using shrink tubing is that you protect the bead and also make sure that it doesn't come in contact with other parts like screws or other beads which in some cases affects the measurements and also affects the dampening that you are trying to achieve to stop oscillations.
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Old Yesterday, 5:23 am   #88
Fourlegsgood
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Default Re: Free Standardised Valves

Quote:
Originally Posted by frankmcvey View Post
Y' mean a bit like this one, David?

I was lucky enough to score a few B9 Cinch plugs!

Found a McMurdo octal plug as well, so an octal break-out box will be next when I get a few minutes spare. Don't know whether to scratch my watch or wind my ass at the moment...

Cheers,

Frank
Good man for lining up the grooves in the screw heads. That's always nice to see. Whether true or not I was told that the 'good practice' was to line them up vertically in locations which would be painted so that the paint flowed out of the groove. That might just be the equivalent of an old wives tale though. (Are we allowed to say old wives tale in these pc times?)

Nick
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Old Yesterday, 5:43 am   #89
mole42uk
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Default Re: Free Standardised Valves

Is there anyone who would care to send me a valve to test on my Sussex?
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Old Yesterday, 5:53 am   #90
Fourlegsgood
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Default Re: Free Standardised Valves

Quote:
Originally Posted by mole42uk View Post
Is there anyone who would care to send me a valve to test on my Sussex?
I have valve 6AU5GT Number 5 and it is available. PM your name and address address and I will message you with my PayPal details for you to pay postage. It seems to be about £4.40 for signed for 1st Class delivery.

Nick
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Old Yesterday, 9:23 am   #91
David Simpson
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Default Re: Free Standardised Valves

I actually used h/shrink sleeving, but kinking the wire or a wee blob of superglue would do.
I agree with Nick, I always try & line up screw slots on just about anything. Frank has set us a good example.
Hopefully, Nick & mole42uk have sorted out postage. I guess I'm out of the loop now regarding who has what 6AU5GT valve, but please keep posting graph pictures on the thread.
I'll let folk know when I have some of those 6AQ5's available.
There is a picture attached showing more B9 adaptors. a B9D magnoval(PL500's etc.) & a B7A(QQV06-40's etc.). Both have ferrite beads inside & are fully encapsulated in araldite. (My macro photography are skills are still lacking).

Regards, David
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Old Today, 12:33 am   #92
frankmcvey
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Default Re: Free Standardised Valves

Thanks for the comments, Martin. It's always good to get feedback, even after 55 years in the trade. As David mentioned, a wee dab of superglue works fine to prevent the ferrite bead moving around. I'm not that worried about the bead's proximity to the valve base securing bolt: it's brass and won't affect anything at all. Bästa hälsningar, och lär inte en mormor att suga ägg!

Nick - lining up screw slots. Yup - as a young apprentice, I had a workshops instructor in the mid-to-late 60's who must have seen a spark and he took me under his wing. I turned in a test job and his comments were that it was fine, but I should line up my screw slots. I asked him why, and all he said was "It's the difference between a tradesman and a craftsman, boy." I've never forgotten it, and it's second nature now to do it.

David, thanks for your comments as well. We came up through the same hawse-pipe and training regime; I've seen photos of your own outstanding workmanship, and I count any accolade from you as praise indeed.

Nick, yes - please send me the 6AU5GT and I'll run it through my Taylor 45C and DC valve testing regime. PM me with your PayPal email, please.

Awra best,

Frank

Last edited by frankmcvey; Today at 12:48 am.
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