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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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4th Mar 2021, 7:08 pm | #21 |
Octode
Join Date: May 2016
Location: Oxfordshire/Bucks borders, UK.
Posts: 1,604
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Re: Is Shed Storage Detrimental To Valves?
Almost certainly the main issue with shed storage, if it's typically cold and damp, can be tarnishing of any contacts/switches in the entire set. Possibly moisture intake from paper caps etc.
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4th Mar 2021, 7:43 pm | #22 |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,573
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Re: Is Shed Storage Detrimental To Valves?
Hi.
Over a decade ago I put a 6F23 valve out in the garden to see how the pins corroded. I was quite surprised to see hardly any tarnishing of the pins despite the valve being out in the open for around 10 years. Also, back in the mid 1990s I bought a large box of valves at our local boot sale. The box was the type TV service engineers carried in their vehicles. It had many dividers so generally protected the valves quite well. What did surprise me was that some of the valves had a severe amount of green corrosion on the pins. I thought that it must have been something more significant than just high humidity to cause that level of corrosion. Maybe the valves were stored with something likely to cause corrosion? I read somewhere that some Mullard Kradlepak valve boxes which contain a blow moulded plastic tray can be responsible. Outgassing from the plastic perhaps? OT, but most sheds have tanalised timber in their construction and I read that ordinary zinc plated nails/screws will readily corrode in contact with the wood. I assume this would only apply to the fastenings holding the sections/cladding together as opposed to surface contact of stored items. Regards, Symon |
4th Mar 2021, 8:12 pm | #23 |
Octode
Join Date: May 2003
Location: Belper Derbyshire
Posts: 1,935
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Re: Is Shed Storage Detrimental To Valves?
I would think the valve out in the open would survive that environment better as it would have plenty of airflow around it and therefore dry pretty quickly. It would also get wet with nothing much chemically stronger than rainwater. A valve in a valve box wrapped in paper would tend to keep the damp in and also be affected by other chemicals out gassing from the paper and cardboard as well as other chemicals (paint, creosote, cleaners ECT.) in its vicinity in which it is kept.
B9a and B7g valves tend to be worse than any other valve for randomly cracking the glass base across one or more pins even with no apparent bending of the pins. Possibly as a result of stresses being left in the glass during production. A quick hot/cold change is then enough to allow the crack to start. I haven’t got that many older octal valves with a pinch seal but would believe that these would survive better having more glass to run the lead out wires from. Christopher Capener
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4th Mar 2021, 9:36 pm | #24 |
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,733
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Re: Is Shed Storage Detrimental To Valves?
All the later valves & readout tubes with a glass base can suffer from rusting/corrosion of the pins, which can then crack the glass seal, even equipment that looks clean & corrosion free can be affected, such as these two readout tubes which suffered this way.
Having said that equipment with signs of poor storage* & heavily corrosion equipment has a higher chance of pin corrosion & valve failure as a result. I've noticed some older Burroughs readout tubes are better protected with extra sealing material around the pins. Miniature neon lamps can suffer in the same way as the leads are copper plated iron/steel? They can drop off circuit boards as well as crack. *Trouble is most old equipment seems to have been stored badly at some point over the years. Edit: Could dissimilar metal corrosion between the pins & the socket contacts also be a problem? David Last edited by factory; 4th Mar 2021 at 9:53 pm. |
4th Mar 2021, 10:20 pm | #25 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,936
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Re: Is Shed Storage Detrimental To Valves?
Some pins seem much more vulnerable to corrosion than others.
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4th Mar 2021, 10:42 pm | #26 | ||
Hexode
Join Date: Jan 2013
Location: Wigan, Lancashire, UK.
Posts: 372
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Re: Is Shed Storage Detrimental To Valves?
Quote:
I have since tried the ECL86 that I believed to be faulty in my Hacker Gondolier GP42. I got the same distorted sound whichever other ECL86, I tried pairing it with. I had already cleaned the pins of the valve with some fine sandpaper. |
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4th Mar 2021, 10:58 pm | #27 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,567
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Re: Is Shed Storage Detrimental To Valves?
There should be sound with one ECL86 as already stated. It won't be loud but it should be OK. Still think there is another problem. Try the ECL86 in the other socket. Does one socket give sound and the other doesn't?
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4th Mar 2021, 11:01 pm | #28 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Is Shed Storage Detrimental To Valves?
It's not wise to use an output valve that is thought to be faulty as it could damage other components like the output or mains transformers.
Running a push-pull amplifier with only one output valve carries the same risk as common cathode bias will cause the remaining valve to thermally runaway. The GP42 has separate cathode bias but the HT voltage will rise and this might also cause a problem. Some voltage measurements of the anode, cathode and grid of both the triode and pentode of both valves will help us determine the fault condition. |
5th Mar 2021, 10:47 am | #29 | |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
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Re: Is Shed Storage Detrimental To Valves?
Quote:
That is the best advice. List the voltages around the output valves.
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5th Mar 2021, 11:12 am | #30 |
Octode
Join Date: May 2010
Location: Grantham, Lincolnshire, UK.
Posts: 1,174
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Re: Is Shed Storage Detrimental To Valves?
Some other points.
Valve pins are carefully made so heating and cooling don't stress the glass and crack it. At the moment I can't find exactly what metal is used, but not iron, lower thermal expansion? In the good old days, before central heating, my dad used to store valves in the timber shed, never a problem. This must have lasted from the 50's until 2008 when he died. Do not, under any circumstances, store anything in a steel container! They have no ventilation and sweat like crazy. Understandable really since the container has to be near water proof whilst being shipped and the only vent holes are tiny little ones only used for pressure equalisation. I have found that the metal sheds, Youngmans, are really very good for storing because they have lots of ventilation, never had problems with condensation. Timber sheds are also good, but must have large vent holes, 3" or so. If store in the loft then make sure there is a good draft through the eaves. I wonder if it is air movement that keeps them good, not had valves going white after decades of storage. |
5th Mar 2021, 12:10 pm | #31 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,852
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Re: Is Shed Storage Detrimental To Valves?
Some years ago I acquired a heap of valves from a University storeroom - they were in mint condition, even the beautiful coloured boxes from the 20's & 30's. A couple of years back I was given large amount of "silent key" valves, which had obviously been stored in a damp loft or shed - the amount of "Mank" was horrendous as was the pin corrosion. Also, many turned out to be useless "pulls".
Regards, David |
5th Mar 2021, 2:43 pm | #32 | |
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,733
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Re: Is Shed Storage Detrimental To Valves?
Quote:
I wonder if they did further cost cutting, as some later ones go rusty, but older ones have green corrosion instead. David |
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5th Mar 2021, 6:52 pm | #33 |
Octode
Join Date: May 2010
Location: Grantham, Lincolnshire, UK.
Posts: 1,174
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Re: Is Shed Storage Detrimental To Valves?
According to Materials and Techniques for Electron Tubes by Kohl, it isn't straightforward.
There are different grades of glass, hard or soft. Softer glass is used on things like CRTs, harder glass on things like power valves. Softer glasses have to be pumped out at much lower temperatures. Softer glasses use lead in wires made from copper clad iron-nickel alloy known as Dumet. Harder glasses use lead in wires made from tungsten. Harder glass are more expensive it would seem. It is pointed out that the tube is no stronger than its weakest link, voltage breakdown, corrosion resistance, contact resistance etc. European valve manufactures made a good job, the fact that 99.999% plus of my valves are still high vacuum after decades rather suggests this. But, things like Nixie tubes could well be made to lower standards, as David points out, and in the commercial competition could have been at a reduced standard? The photo in post 32 looks good to me? But, for anything that was intended to be used the best material was used? Just look at the quality of the cathode coatings used in the 50's and 60's, vastly better than the stuff used now when it spits and pops. |
5th Mar 2021, 8:52 pm | #34 | |
Hexode
Join Date: Jan 2013
Location: Wigan, Lancashire, UK.
Posts: 372
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Re: Is Shed Storage Detrimental To Valves?
Quote:
I have now tried the AL42 unit with two PCL86s. The unit works. As ECL86s are very expensive now, I think I am going to go down this route and use a 13 - 14v mains transformer to supply the PCL86 heaters. Another member on here recently started a thread about the same idea, but I haven't been able to find it again. As the AL42 looks like it has been stored in damp conditions, I will give it a service replacing the grid coupling capacitors, C6 and C7, (0.05uF), R6 and R7 (220k 0.5w), (which can cause distorted output if they go high in value), all the electrolytic capacitors and any other resistors that are out of tolerance. Last edited by Fidelity Fan; 5th Mar 2021 at 8:57 pm. |
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5th Mar 2021, 8:54 pm | #35 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,394
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Re: Is Shed Storage Detrimental To Valves?
If you value a collection of valves (and if not, then why are you collecting them?...) at least invest a few pennies and a few seconds per valve in putting each in a "gripseal" polybag. These can be bought in 100s or even 1,000s, a while back I bought 1,000 of a size that accomodates typical B7g/B9a signal valves for about £7, I probably have about 800 left! This will at least greatly slow the rate at which moisture and consequent corrosion affects them, another advantage is that it reduces the impact of glass-to-glass clash in a bulk box. Anything of any significant value (6V6 upwards) deserves further cosseting in something like a plastic sandwich box with a clip-over lid, several middling-size bottles can be accomodated in a typical box. If this sounds like too much trouble/time/space, re-appraise why they're being kept!
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5th Mar 2021, 9:51 pm | #36 | |
Hexode
Join Date: Jan 2013
Location: Wigan, Lancashire, UK.
Posts: 372
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Re: Is Shed Storage Detrimental To Valves?
Quote:
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5th Mar 2021, 10:57 pm | #37 | |
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,733
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Re: Is Shed Storage Detrimental To Valves?
Quote:
Looking closer at a pin removed from that valve it's clear to see the different parts used, all seem to be magnetic. The machine they are from has quite a bit of corrosion on the casing, the CRT worries me too as the side connections have rusted, hopefully it'll be OK as it's not an easy to obtain one. David |
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5th Mar 2021, 10:58 pm | #38 |
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,733
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Re: Is Shed Storage Detrimental To Valves?
The older Burroughs readout tubes were definitely better made, here is a faulty one from 1963 (the 6 is O/C but still usable for test gear that only needs lower numbers), I hope it's clear to see the dark green coating where the pin passes through the glass, this must help prevent corrosion getting near the seal.
And the later Burroughs tube from 1966 with rusty pins, as it is completely dead I removed a pin, this appears to be made from one material only. The replacements were very hard to find as it needed the decimal point, which ruled out all the cheap tubes & Russian types. The fact readout tubes have far more pins than a normal valve and they are often very closely spaced may help contribute to increased seal failures. David Last edited by factory; 5th Mar 2021 at 11:03 pm. |
6th Mar 2021, 12:10 am | #39 | |
Pentode
Join Date: Sep 2018
Location: Maldon, Essex, UK.
Posts: 227
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Re: Is Shed Storage Detrimental To Valves?
Quote:
It worries me that someone out there could be unaware of this requirement. One of my Bench Power Supplies is fitted with a (nominally) 1 minute B7G-type Thermal Delay Switch , to allow the NGT5s to clear the "fog" which forms on the glass on switching-on the heaters . Laurie |
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6th Mar 2021, 1:51 am | #40 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Re: Is Shed Storage Detrimental To Valves?
One type of valve that does not cope with bad storage is the Acorn series. Because of the unusual way the valve was manufactured, the 5 "waistband" pins are made of an alloy (iron/copper?) that corrodes badly (becomes covered in a black oxide), and the corrosion continues between the glass/metal seal and the vacuum leaks away. I think that such corrosion may even have got started as they were shipped in the cold, dank holds of the Liberty ships as they sailed the North Atlantic.
B
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