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  #11  
Old 6th February 2011, 11:58 PM
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BOONDI BOONDI is offline
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Default Re: When to change valves?

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Originally Posted by Revoli View Post
Oh dear. Does that mean I should be changing my wad6550 valves that are 10 years old.......

Can anyone recommend what is worth trying in this amp in terms of valve upgrade. I knOw it's somewhere in the forum....

Unless you have noticed a difference in sound quality or are having distortion problems, I would take my time here. Some transmiter triodes and etc have been run for over 50 years without a change. I think the world record is 80,000 hours for a pair of 845 running continually for 24 hours a day 7 days a week. They were retired at 80,000 hours, but the radio station kept them as spares.

If you only listen a couple of hours a week they probably have less than 5000 hours on them. I'm sure they will run reliably for a few more weeks.
Well at least until you have had time to investigate further....
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Old 7th February 2011, 12:36 AM
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Default Re: When to change valves?

80,000 hours ?

That's only a gnats over 9 years.

Hardly run in.

I think the secret was the 24/7 usage.
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  #13  
Old 7th February 2011, 12:39 AM
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Default Re: When to change valves?

Hi Revoli and Boondi,

Boondi's right about not changing them if they're not worn out but they tend to fade without notice over a long time so having a spare set to try from time to time is always a good idea.

The quote rang bells, and here it is in full from what was the Svetlana website no less,

Small-signal tubes almost always use oxide cathodes. Good-quality tubes of this type, if operated well within their ratings and at the correct heater voltage, can last 100,000 hours or more.
The world record for lifetime of a power tube is held by a large transmitting tetrode with a thoriated filament. It was in service in a Los Angeles radio station's transmitter for 10 years, for a total of more than 80,000 hours. When finally taken out of service, it was still functioning adequately. (The station saved it as a spare.) By comparison, a typical oxide-cathode glass power tube, such as an EL34, will last about 1500-2000 hours; and a tube with an oxide-coated filament, such as an SV300B, will last about 4000-10,000 hours. This is dependent on all the factors listed above, so different customers will observe different lifetimes.

I'd agree with that, I've worn out a couple of sets of 6550C in about 2 years each set but not a set of 300B in 3 years! EL34/6550/KT88/EL84 etc fit into that 2000 hours group if run hard. They will last a lot longer if bias current is set a little lower. The small signal valves will last maybe 10 times that.

My rec would be Mullard ECF80s Svet 6550C or the reissue Gold Lion KT88s (very good indeed) and a couple of Russian coke bottle 5u4 which they label as 5u3 rects. Yes rects do sound different!
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  #14  
Old 7th February 2011, 11:59 AM
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Default Re: When to change valves?

Thanks Richard, I was looking for that all last night. I always have a set spare just in case.

Revoli, if I were you, I would get a set of the Svetlanas or Golden lion reproductions. When you get them, don't throw the old ones out if they are still working. Keep them as your spares. This means that if one of your new ones should fail after a short time, you have no wories about new and old valves not being matched etc etc..... Just change the set. You will also still have music while you wait on a replacment......

Now all I have to do is figure out what I am going to do with all the old valves I no longer have amps for..... Oh well, win some, lose some.....
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