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Do i have to replace all my power tubes

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Do i have to replace all my power tubes

Postby cminor7b5 » 06 Oct 2017 17:39

I have an integrated Chi-fi amp which I'm very pleased with.

After many years one of the original EL34 tubes went bye bye.

I did some research and replaced all four EL34's with new, matched Mullard EL34s.

Is this necessary or could I have just replaced the one tube?

The main reason I asked is I preferred the sound of the original tubes.

I've let the Mullards break in completely and still feel this way.
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Re: Do i have to replace all my power tubes

Postby Ottermel » 06 Oct 2017 17:55

I replace only the bad tube and re-bias them all again!
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Re: Do i have to replace all my power tubes

Postby gofar99 » 06 Oct 2017 20:29

Hi, It kind of depends on the amp. Sometimes a new tube will have a slightly different sonic signature than one from the same brand of earlier manufacture. Also even though you can bias them they may have different gain and may introduce distortion. I always replace in pairs. With the cost of matching now very reasonable with most of my suppliers doing it for about $1-2 it is cheap insurance that the tubes will play well together.
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Re: Do i have to replace all my power tubes

Postby cminor7b5 » 06 Oct 2017 20:53

gofar99 wrote:Hi, It kind of depends on the amp. Sometimes a new tube will have a slightly different sonic signature than one from the same brand of earlier manufacture. Also even though you can bias them they may have different gain and may introduce distortion. I always replace in pairs. With the cost of matching now very reasonable with most of my suppliers doing it for about $1-2 it is cheap insurance that the tubes will play well together.


This is what my research led me to believe.

Also the amortization costs seem pretty low if the tubes last several years.

If I had loved the Mullards I don't think I would have asked this question, I would just say that's the cost of hi-fi maintenance and been happy.
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Re: Do i have to replace all my power tubes

Postby theclosetguy » 08 Oct 2017 19:30

There is a mystic surrounding Mullard El-34's that doesn't make sense. When I started my tube journey 20 years ago I bought a Dynaco St-70 and it was fitted with Mullards. I hated the sound. "dark" is the best way to describe it. A bit of research and the consensus was just that, Mullards are heavier than other El-34's/6CA7's. Replaced them with a set of Brown Base Amperex's. At that time, NOS Tubes were still reasonable in price. So rolling different power tubes did not require an additional rent payment. Forget it now.
If you can bias each tube on its own, replace just the one. If You have auto-bias replace in pairs.
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Re: Do i have to replace all my power tubes

Postby Slate Audio 2015 » 11 Oct 2017 12:43

Hello. The cost of EL34 tubes is very reasonable. Why wait till another tube fails, then another. Change them all at the same time, that way you will be running on full performance that can be relied on. As for the type of EL34, most are made at the same factory, either in the Eastern Bloc or the States under licence, then branded. Electro Harmonics for example will serve just as well as some over hyped re-branded types, and will not make you feel that you have been harvested.
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Re: Do i have to replace all my power tubes

Postby hossfly10 » 13 Oct 2017 04:59

Ottermel wrote:I replace only the bad tube and re-bias them all again!


IMHO that is a bad idea. You should always replace them in pairs at the least on each channel.
Reason being...yes, if you have manual bias, you can bias them into matching output, however, if the tubes are wildly mismatched, it will stress them and can cause early failures.
It is just good practice to be proactive with power tube replacement, because if one goes south quickly it can become an expensive amp repair, and is much less likely to happen with matched tubes instead of "force matching" them with bias, for lack of a better term.
Plus it gives you a spare in case one does lay down unexpectedly.
As I said, just MHO, but when you are talking about a maintenance item costing $100-200 for a really nice pair of tubes in a $1000+ amp, it really just makes long term sense.
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Re: Do i have to replace all my power tubes

Postby Ottermel » 13 Oct 2017 17:51

hossfly10 wrote:
Ottermel wrote:I replace only the bad tube and re-bias them all again!


IMHO that is a bad idea. You should always replace them in pairs at the least on each channel.
Reason being...yes, if you have manual bias, you can bias them into matching output, however, if the tubes are wildly mismatched, it will stress them and can cause early failures.
It is just good practice to be proactive with power tube replacement, because if one goes south quickly it can become an expensive amp repair, and is much less likely to happen with matched tubes instead of "force matching" them with bias, for lack of a better term.
Plus it gives you a spare in case one does lay down unexpectedly.
As I said, just MHO, but when you are talking about a maintenance item costing $100-200 for a really nice pair of tubes in a $1000+ amp, it really just makes long term sense.



I only replace them with the tubes from the same manufacturer and run them in about 20 hours and so far have not found appreciable differences in sound (those are 6550's).
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Re: Do i have to replace all my power tubes

Postby davidsrsb » 15 Oct 2017 04:51

Even from the same manufacturer, a new tube will have higher current and gm than a well used tube. This will cause a big increase in even harmonic distortion, usually cancelled out in a push-pull stage.
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Re: Do i have to replace all my power tubes

Postby OneyedK » 15 Oct 2017 17:21

cminor7b5 wrote:The main reason I asked is I preferred the sound of the original tubes.

Yes, you have to replace the entire quad...
You can replace one and bias it properly, but when in use, it will be very different than your other tubes and add, as somebody else already mentioned, even order distortion.

Your speakers are very revealing and require a fair bit of power to sound their besst. (I love Totem products!!!)
So in this case, the Mullards can be a bad match.
If you want to try Chinese tubes again, try to get hold of a set of TAD tubes. They offer a selection of chinese tubes, tested and rebranded with their TAD label. They also offer a one year warranty. I do like current production chinese power tubes, but they can be erratic in the first hours of use...
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Re: Do i have to replace all my power tubes

Postby Allan W. » 19 Oct 2017 00:31

Based on your "Many Years" statement, I'd replace them all. Years is the key word. Nothing like have a few spares either.
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Re: Do i have to replace all my power tubes

Postby theclosetguy » 19 Oct 2017 02:54

Slate Audio 2015 wrote:Hello. The cost of EL34 tubes is very reasonable. Why wait till another tube fails, then another. Change them all at the same time, that way you will be running on full performance that can be relied on. As for the type of EL34, most are made at the same factory, either in the Eastern Bloc or the States under licence, then branded. Electro Harmonics for example will serve just as well as some over hyped re-branded types, and will not make you feel that you have been harvested.


So are you saying the Chinese do not manufacture tubes and they are only made in the USA or The Eastern Block? Where does this wrong information come from? Do you know something about tube manufacturing that no one else know?
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Re: Do i have to replace all my power tubes

Postby Slate Audio 2015 » 11 Nov 2017 17:23

Please read my reply again. "Most"(but not all)are made at the same factory, either in the Eastern Bloc or the States. Of course valves are produced elsewhere as everyone knows. The point is, that it is entirely possible to get a good quality valve without paying the earth, as it is often the case that various branded valves will originate from the same factory. My reference to the Eastern Bloc and the States was merely an example.
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Re: Do i have to replace all my power tubes

Postby solvin_dk » 12 Nov 2017 14:19

Of curse you have to replace all of the tubes. If one of your headlight in you car fail, you most replace both of them. That's a fact, soon the other bulb will die. I have been building many tube-amps for the last 25 years. So trust me. You have to replace all tubes.

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