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Worn Valves

Avonessence

Avonessence

Hiking Consistency Rapporteur
When power valves start to get to the end of their life do they exhibit any specific audible characteristics?

The reason I ask, is I am hearing a slight breaking up at the top end on my current EL34's valve which are approx 15-18 months old, and have seen a fair bit of use, approx over 1500hrs.
 
That's one possible symptom. With that amount of use I'd be inclined to have a spare set handy. In fact, I had the same sort of symptom recently with 5881s, and swapped in new ones and all OK. I still ned to test the originals though.
 
Hi toprepairman,

Would you say that what I am experiencing is a symptom of the valves getting worn or at the end of their life?

Best

James
 
toprepairman said:
EL34's should last a lot longer then 1500 hours.
Click to expand...

It'll depend on how hard they are being pushed, biasing etc.. For example I used to run an amp with 8 EL34s that were just about ticking over to give around 40-50 w/channel. The EL34s on that beast lasted ages and are probably still going strong. However another amp I had used 2 EL34s a side yet was rated at around 60w/channel. Those didn't last that long and were changed out after about 18 months.
 
Valves are like car engines. A 6.5 litre V8 used well within its capabilities will last much longer than a 1-litre straight four, and require a lot less attention. A friend used to be a BBC transmitter engineer in the eighties. He told me that they were about to replace some valves in the Rugby transmitter. The ones in use were the originals, and were first commissioned some time in the 1930s. These things were about three feet high. As already suggested, design or source equipment which will only ever be called upon to deliver a fraction of its potential power.
 
Hi James.
It really depends on what exactly do you mean by 'slight breaking up at the top end'.
Different amps do run the valves differently and both the amp manufacturers and the end user can abuse the valves.
Curiousely a lower power amp can wear them out quicker than a higher power one.
Also some valves may be made to a poorer quality and also not last so long.
As long as the max anode dissipation is not exceeded and cathode current is not excessive then they should give more than 1500 hours life.
 
I'd also suspect, although I've had little to do with valves for a long time, that there are some out there of less than exemplary manufacture. I'd probably trust Russian ones, because the Russians never stopped using them for military purposes. However, I suspect some manufacturers, probably in the Far East, have jumped on the bandwagon, now that valves sell for such ridiculous sums, and turn out cheap ones which just look attractive. In the old days, there were the likes of Mullard and a small number of other top makers, and also some inferior ones you wouldn't touch.
 
I do remember that the miniature valves we used in the sixties (such as the ECC83 and others with B9A bases) and even the larger octal ones had markings on the glass envelope, such as the maker's name and logo and valve code number, which were applied in some sort of delicate white paint. This used to wear off with even a small amount of handling. Sometimes you had to get hold of the service sheet to know which valves were in a piece of equipment. Given the skill with which other items can be counterfeited nowadays, it wouldn't take much expertise to clean off any existing printing and substitute "Mullard" or something equally desirable, selling the result as new old stock.
 
Mullard and others also used etched codes in the glass bottle so the etching would reduce the chance of encountering a fake.

Far Eastern valves range from good to awful as far as durability and consistency goes. Some Russian production has the same problem. It all comes down to spotty QC.
 
Mignun said:
It'll depend on how hard they are being pushed, biasing etc.. For example I used to run an amp with 8 EL34s that were just about ticking over to give around 40-50 w/channel. The EL34s on that beast lasted ages and are probably still going strong. However another amp I had used 2 EL34s a side yet was rated at around 60w/channel. Those didn't last that long and were changed out after about 18 months.
Click to expand...

My amps can deliver in excess of 100w from four EL34s, although I rarely push them beyond a few watts.
The manufacturer assures me that he has seen examples of his amps running happily (And within spec) on fourteen year old valve sets.

I bought my amps in 1997. I had one valve failure on the originally fitted Edicrons. (Edicron as I understand it purchase Eastern European valves which they then rebrand/grade etc and sell under the Edicron name to the trade only.)

I then swapped to a set of Svetlanas which I'm still using, although one of them has failed and is currently replaced by an odd Edicron. Can't say the amp with the odd Edicron performs differently to the other in any audible way.

Mull
 
ClaraBannister said:
Valves are like car engines. A 6.5 litre V8 used well within its capabilities will last much longer than a 1-litre straight four, and require a lot less attention. A friend used to be a BBC transmitter engineer in the eighties. He told me that they were about to replace some valves in the Rugby transmitter. The ones in use were the originals, and were first commissioned some time in the 1930s. These things were about three feet high. As already suggested, design or source equipment which will only ever be called upon to deliver a fraction of its potential power.
Click to expand...

Eddie, who manufactures the Papworth range, also used to work as a transmitter engineer and told similar tales of some of the enormous transmitter valves out there.

He is also entirely comfortable getting 100w plus out of four EL34s in push pull. :)

Mull

P.S.

One evening I came home from work at dusk and flipped the power switches on my amps as I shot though to the kitchen to put the kettle on.

A minute or so later I returned to the living room to see the whole place lit up red. One of my amps had all four valves glowing cherry red! I switched off and called Eddie. He had me taking the base off the offending amp and talking to him, but we found nothing remarkable and I decided to take the amps to him for a service the following week.

A little later, where I had turned the amp over to take the base plate off, I found a single dress making pin, blued as if subjected to considerable heat.
I concluded that this pin had somehow found its way into the amp and shorted something, then fallen out as I looked at the amp.

Eddy checked both the amp and the four valves and declared all OK.

Valves are pretty damned tough.

Mull
 
ClaraBannister said:
I do remember that the miniature valves we used in the sixties (such as the ECC83 and others with B9A bases) and even the larger octal ones had markings on the glass envelope, such as the maker's name and logo and valve code number, which were applied in some sort of delicate white paint. This used to wear off with even a small amount of handling. Sometimes you had to get hold of the service sheet to know which valves were in a piece of equipment. Given the skill with which other items can be counterfeited nowadays, it wouldn't take much expertise to clean off any existing printing and substitute "Mullard" or something equally desirable, selling the result as new old stock.
Click to expand...

Yes, there's quite a trade in doing just that. Ironically the replacement logos printed on the valves don't rub off so are a bit of a giveaway.

As Jay pointed out Mullards have date codes etched on the glass so are fairly easy to identify. Other manufacturers can be a bit more tricky.
 
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