How do you know when to change tubes?

When I hear a hissing noise and the bicycle starts to wobble.

Gritty treble was the give away on my AI500. It was pretty obvious. My Graaff GM50 didnā€™t throw a valve, so I donā€™t know if this failure signature is common or ubiquitous.

Youā€™re right - my apologies, I didnā€™t know where you live.

It is from a British radio comedy programme, a regular sketch called ā€œMornington Crescentā€, which is the name of a station on London Underground, also known as ā€˜tube trainsā€™ or just ā€˜The Tubeā€™, Nominally it involves opposing tesms alternately naming the stations at which one must change to travel from a named starting point to that destination: hence the relevance to the title of this thread. The game is haphazard and random - and that is the humourā€¦

On your intended meaning, whilst you may not be able to take an amp to the dealer, conceivably you could take individual tubes, perhaps not all, just one of each type as their lives may be similar: if one in a particular stage of the amp is reaching end of life or dropping in performance, the chances are that any paired ones would be not far off the same.

if i understood well, you canā€™t putt off one tube of the amp socket?

No apology necessary! I was amused by it, even if I didnā€™t understand it. I guess itā€™s my turn to apologize; I should have included an appropriate emoticon.

Itā€™s just about as much trouble to retrieve it from its spot in my audio console as to carry it in. I think Iā€™ll take Pederā€™s advice and just give my good husband a hand as best I can and carry it in and change them all out. They do have quite a few hours on them. Then I can quit obsessing over it.

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Valves are interestingā€¦ the longer you keep them powered up, the longer they last by a significant marginā€¦ so best keep valves powered up for as long as you can. Valves and environmental considerations donā€™t really go hand in hand. Other than excessive sonic or performance changes I look for excessive sooting marks on the inside of the glass casing as a sign of increasing chance of failure.
And as far as Mornington Crescentā€¦ I think most in the UK who listen to Radio4 will be aware of itā€¦ it sort of has become a British metaphor for made up nonsence rules.

You should say ā€œmost in the UK who listen to Radio 4 panel gamesā€, which is a seriously small proportion of the whole UK populationā€¦
Best

David

You say that, it always surprises how deep BBC culture goes across allā€¦ true I doubt many very much younger people might be aware of such thingsā€¦ but you get to middle age and I suspect itā€™s quite differentā€¦ I think we underestimate just because we are a diverse society how some things seem to pervade throughā€¦ I saw an advert on the London Underground that made some reference to the alternate association of Mornington Cresent ā€¦ I suspect that wouldnā€™t really work if it was too niche.

BTW I donā€™t listen to Radio 4 panel games.

Hi Simon,

It is what you say that I find interesting. If you compare valves to a incandescent light bulb then yes you will shorten their life if you constantly power them on and off but amplifier power valves will have an average life of +/- 3000 hrs. At least that is what i found with amplifiers using EL-34 and KT-88 valves.

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When visiting The Hammersmith Apollo, I donā€™t usually change tubes. I always take the Piccadilly line.

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Very funny :grinning::clap:t2:

Thatā€™s the other difficulty I have. It sounds like many tube users have externally mounted tubes so itā€™s fairly easy to look for an off color tube, or perhaps check that their appearance is similar whether on or off, or pull one out for testing. My tubes are hidden Inside a rather large case of aircraft aluminum (which must contribute to its hefty 51 pounds).


Itā€™s that 51 pounds that makes checking tubes somewhat challenging. It also has three feet which terminate in sharp points. Just lifting all that weight out of its spot in my stereo console is fraught because those spikes scratch, and then where can it be safely put down where those spikes wonā€™t damage something. Putting it back is no fun either because you canā€™t slide it. Then you have to aim those spikes at little protective cups and hit the sweet spot where thereā€™s a little indent for the spikes. Itā€™s a challenging fellow to own when itā€™s time to change tubes.

Iā€™m sure for the right price my audio fellow will make a house call. Too bad I canā€™t hook up with a fellow audiophile and tube roller in my neighborhood.

I nearly gave myself a hernia the first time I put the NAP500 heard unit into the space Iā€™d prepared for it. It weighs 55lb and Fraim glass slides off its balls very easily (which then jump out of their cups and disappear under the rack) but at least I could rest it part way inā€¦
A set of Herbies small Gliders in place of the cups might help, if you could engage the rear spike(s), then slide it in on that/those and have your assistant put the remainder in place once the front spike(s) is/are above the shelf. Iā€™ve no idea what they will do to the sound quality, I use a set under speakers on a marble tiled floor, the system sounded really harsh when I fitted the spikes and Gliders but the harshness had completely gone on our next visit 3 months later so I think they bed in a bit. (This system is in our second home 1000 miles from our main one.)

you canā€™t unscrew the top cage without moving it?

Absolutelyā€¦ in the early days of valve computers with hundreds and hundreds of valves keeping the device powered up, at huge power draw, the significant benefit was massively increased reliability.
Of course bad design, just like semiconductors, can prematurely shorten the life of a valve with it powered on.
My largest valve linear power amplifier uses a ceramic tetrode GU74Bā€¦ that is a 1kW rf power ampā€¦ replacing it is a little involved as is it needs rebiasing, so when in use over closely spaced short periods I keep it on, and switch off only for extended periods of inactivity. In 12 years I have had to only replace once.
Unfortunately because of its design the casing is covered in heatsink vanes for forced cooling, so you canā€™t see any sooting, but there are control electronics to indicate probable failure if failure is not total.
My very much smaller valve audio amp can be visually inspected

Nope. Headroom is only about 2.5ā€.

The glides Yeti suggested might be worth looking into if they would allow us to slide the beast in and out of its spot. Thatā€™d help a lot.

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