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16th Jul 2006, 1:44 pm | #1 |
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Testing PL509s on an Avo mk3
(...not sure if this should go in components, test gear or in the TV section - I've gone with the latter as it's the Tv folks who are most likely to have tried, sorry moderators; please move as required...)
I've been going through some of my valves of late and have a number of PL509 / 19s I'd like to test. I know some are especially tired (they got a bit cooked in a driveless G6) and it would be good to sort the wheat from the chaff ready for the next battle! As my Avo Characteristic meter (mk3) is on the bench I'm wondering if I can use that? My data books for it are too early to mention theses valves so I'm not too sure? Has anyone ever tried these on an Avo, and if so, do they have the set up details? I know some maintain that the best valve tester is the circuit the valve came from, (fair enough), but with the set up details this would be much more straightforward....maybe! |
18th Jul 2006, 8:51 pm | #2 |
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Re: Testing PL509s on an Avo mk3
Hello Stewart,
I felt guilty leaving out in the cold with no answers to your query! To be honest I never found valve testers of any kind capable of reliably testing line output, boost diodes or heavy current rectifiers. You need to slap' em in an old Decca Bradford for at least an hour and hope there are no fireworks... Regards John. |
18th Jul 2006, 11:11 pm | #3 |
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Re: Testing PL509s on an Avo mk3
There's no need to feel guilty about it, as a Valve Tester does not show up all the faults in a valve, especially one that works at 15khz and under such pressure.
I have been fixing old tellies and some which are now considered old, for over 20yrs, mainly as a hobby. And I have never used a tester once. The best way to test a valve properly is to put it in a set and see what it does. This is better than any valve tester. In fact, in some cases, a valve which shows up at faulty due to low emission is perfectly OK. EF80's, for example, will work down to 30%. Have a look, stick on Ohmeter across the heater pins, give a shake, if there's nothing obviously wrong, stick it in and try it! One other thing - avoid the imported line o/p valves.... Cheers, Steve P
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18th Jul 2006, 11:56 pm | #4 |
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Re: Testing PL509s on an Avo mk3
Many thanks for your thoughts gents...I somehow knew testing in circuit was what was going to be suggested...hard to argue against really, but I was hoping to spare undue stress on my sets. OK...I was being lazy!
No Bradfords here to try them in (oddly I've never even had one pass through my hands), and I don't dare breathe on the G6 lest something goes wrong (and it's hot enough already in the workshop without 21 valves throbbing away) ...so I can see one of my trusty (well they were once) ITT cvc8s being wheeled out. I have quite a few "pulls" here from sets that I've had (if only I still did - better examples than I have now!) so will work my way through them - thankfully all Mullard save a couple of Pinnacle...and oddly a Thorn one! (Why did they do a valve when nothing they made needed it?) Stew |
19th Jul 2006, 7:19 am | #5 |
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Re: Testing PL509s on an Avo mk3
Hello,
I have come across "Thorn" branded valves and suspect they were produced by Thorn Radio Valves and Tubes Ltd for use by their sister companies Thorn Television Rentals Ltd (Radio Rentals, DER & Multibroadcast) and Rumbelows Ltd. Some of these Thorn branded valves were actually made in the Mazda/Brimar factories, whilst others were imported, including Japanese made versions. Both of these Thorn rental/retail companies rented and sold TVs other than "Ferguson" sets, so they needed PL509s and PY500As, etc. Radio Rentals, for example, bought in a large number of Korting 90 degree hybrid colour sets in the early 1970s, to cope with phenomenal demand. Before the takeover of Radio Rentals by Thorn in 1968, they produced a hybrid dual standard Baird colour chassis and bought Baird badged dual standard CTVs from GEC Radio & Television Ltd. The purpose of branding them Thorn, rather than Mazda, was to immediately identify them as the property of TTR and Rumbelows! Needless to say, lots of Thorn valves found their way into sets not sold or rented by Thorn companies. I'll leave you to work out how! Regards, Dazzlevision |
19th Jul 2006, 9:39 am | #6 |
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Re: Testing PL509s on an Avo mk3
You are right, DV - the master parts list used by Thorn that we ordered from included nearly all TV valves - when delivered weekly, they were usually branded "Thorn" and came in plain white boxes with just the number on them. (you forgot about Focus and Easiview)
You'll be glad of the G6s in winter. Regarding testing, one place I worked at, the boss rooted through the bins at night and dragged out any valves, testing them on his Mullard one-arm bandit. If they "passed", back on the shelf they went - you could not reason with him. PL, PY, EY, PCL85 generated repeat calls like it was going out of fashion. Not much better, either, when the new ones were Zaerix or RETRA, complete with brown skid-marks inside the envelopes.
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19th Jul 2006, 8:45 pm | #7 |
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Re: Testing PL509s on an Avo mk3
I agree with Steve, the best way to test PL509's ( and other line output valves) is to put them in a working set. On a PL509 I always check the screen grid voltage (on my Bradford its about 250v) and the - line drive on the control grid which should be at least -70v.
As Steve says its probably best to leave well alone until this heatwave is over. I certainly won't be running my Decca Bradford until the temperatures return to more normal values.
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19th Jul 2006, 9:36 pm | #8 |
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Re: Testing PL509s on an Avo mk3
Hi,
When testing LOP and Boost valves in TVs, I would also give them a gentle tap on the glass envelope with a screwdriver, which can initiate internal flashover or other spurious effects. Any valves that fail this test I consign to the bin. Regards, Dazzlevision |
19th Jul 2006, 9:44 pm | #9 |
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Re: Testing PL509s on an Avo mk3
I suspect that the only reason for testing a PL509 on a valve tester is if you want matched pairs for audio amplifiers. There is no way that a valve tester can come anywhere near simulating the harsh conditions of a line output stage. ISTR that a PL509 can run up to 1.4A peak cathode current which must be rather beyond any valve tester.
I looked in a box the other day and found some NOS EL509 and EL504. I suspect they were used in European rather than UK sets. Maybe I should flog them to audiophools. Do I need to test them first |
20th Jul 2006, 12:36 am | #10 |
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Re: Testing PL509s on an Avo mk3
Only the heaters!!!
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20th Jul 2006, 8:15 am | #11 | |
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Re: Testing PL509s on an Avo mk3
Quote:
No need to test them for the 'phools - just say something about the shape of the anode, and make up a bit of gubbish about the colour of the writing.
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20th Jul 2006, 8:41 am | #12 |
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Re: Testing PL509s on an Avo mk3
I will indeed be waiting for cooler days before running up any of my hybrids to try out my bottles - I'm hot and bothered... and there is a fair chance the sets would be too!
The comments about information on testing these in a characteristic meter only being of use to audiophools is a fair point - so I'm now glad no-one came forth with how to do it! We don't want to encourage that kind of thing! My heart sank when a recent search on a well known auction site for PL509s showed that it may already be too late: The 509 is it seems a highly regarded output pentode with Telefunken branded ones commanding £40! On the one hand I could cry, on the other my retirement fund has never looked better! |
20th Jul 2006, 8:57 am | #13 |
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Re: Testing PL509s on an Avo mk3
I didn't realise that PL509s had such profound implications
http://library.kent.ac.uk/library/ex...p?course=PL509 It's definitely the heat. |
20th Jul 2006, 9:58 pm | #14 |
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Re: Testing PL509s on an Avo mk3
Hi Gents, a quick idea, not fully thought through yet (further thoughts invited), for a cheap and cheerful LOPT valve tester.
1 Dropper or transformer for heaters 2 rectified (1/2 wave?) or straight AC to anode via 250W bulb as load 3 screen supply 250V dc or strap to anode 4 neg supply to grid Plug in and allow to heat up, reduce neg grid volts to get 200mA in anode, reduce 1 or 2 volts further and use current change to find mutual conductance. Even simpler if we have a fixed bias that gives say 200mA with a good valve and read current at fixed bias for other valves. The set is still the ultimate check, but useful if you are not certain of the set.. HTH Ed |
20th Jul 2006, 10:18 pm | #15 | |
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Re: Testing PL509s on an Avo mk3
Quote:
The difference between peak and average currents, the maximum peak anode voltage a valve will withstand etc., means that for power valves not running in class A you really have to test them under maximum operating conditions. This also goes for things like transmitter valves. I have a bunch of 'good' yet used 807s, but only one of them is strong enough for real world class C transmitter duty. Along the same line of thought it might also be worth noting that well used E/PL50x specimens, which fails in line deflection duty, may have sufficient life and emission left in them for light audiophool class A duty. Frank N. |
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