Do you really need to replace all tubes on a tube amp at the same time?

G

gene12586

Member
I have a fender deluxe reverb reissue (tube) amplifier. Some months ago I replaced maybe 3-4 of the tubes because they were starting to cause issues - though I no longer remember which ones I replaced. I think I replaced them with the same tube models (though it's possible one of the replacements was a slightly different model). I'm just reading online now in multiple places that when you replace one or more of the tubes you're supposed to replace all of them. Is that really true? That seems a bit ridiculous and too costly. Or is it ok to just replaced one or several at a time?
Thanks.
 
Its better to replace them all, because the timer starts to run on tubes first power up, so replacing the first worn out one works but then another goes, and another. If you are paying for replacements including fitting, the. Doing them all saves money. That said, most people replace only the faulty ones. In the uk, where tubes are ‘valves’ service engineers were called valve tappers. You tapped each one with your screwdriver, found the dodgy one, and swapped it. Job done.
 
rob aylestone said:
Its better to replace them all, because the timer starts to run on tubes first power up, so replacing the first worn out one works but then another goes, and another. If you are paying for replacements including fitting, the. Doing them all saves money. That said, most people replace only the faulty ones. In the uk, where tubes are ‘valves’ service engineers were called valve tappers. You tapped each one with your screwdriver, found the dodgy one, and swapped it. Job done.
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Thanks. I see; so it's not a functionality issue (i.e., the amp isn't going to sound worse just replacing one or two at a time) - it's actually practical to replace them all at once when one goes.
I was just worried that somehow the amp won't sound as good if replacing one or two at a time. Correct me if I'm wrong.
Next time one of the tubes dies I'll replace them all.
 
That's not what I suggested - they're too expensive to discard if they're fine. If you were paying me to do a tube swap, I'd suggest doing the lot, but if you've determined which one is trouble, and are perfectly happy swapping it - just do that one and save some money. Only you have control over the sound. It's like the tyres on your car - they all wear a little differently. Do you replace ones that are not approaching the legal limit? I don't know about you, but if I see one is worn, or it fails the annual test, I buy one tyre - I do the other one when it needs it. If you have 4, and one is worn out, replacing that one restores the sound. If you hear other issues, then if they are the same type. NOT similar - tubes fall into a number of categories (Dave is the expert here) but some are acceptable alternatives, and sometime just a brand thing, but others have different performance. I remember the old tales that ECC84 could be replaced by a 6N14P - because it had better performance. Something to do with linear vs not linear gain curves, and they were a plug in alternative some swore by, but an ECC84 had different pin connections to an ECC83 - so swapping to different tubes can be risky if you don't understand them!
 
It is very rarely that I disagree with 'our Rob' but this time I must. We must first differentiate between output valves and the rest. Where there are two* OP valves they should be replaced as a pair to keep the push pull stage balanced and minimize hum. This also keeps LF distortion to a minimum but that is rarely of concern to gitists!

"Pre amp" valves do different jobs and their failure modes are different. The first valve might go a bit hummy or 'fizzy' but be perfectly acceptable as a tone stack driver for instance. The PI valve gets a rather hard life with its cathode jacked up to 80V or more so it is quite likely to fail years before any of the others.

Historically valves only ever carried a 90 day warranty. This reflected the random nature of their failure modes. Naturally valves almost always last much longer than that. The failure mode for a valve is complex. Power valves in guitar amps almost always fail catastrophically and not from 'old age' which is basically loss of cathode emission.
Resistors fail high or open. Caps go short but valves can fail all sorts of ways including microhony.

* If 4 OP valves they can be replaced as pairs. Either outer or inner. Swap about for minimum hum.

Dave.
 
My apologies Rob, I was a TAD (boom! Boom!) hasty there!

You make a very good point about "swapping types"? In general...DON'T! Some designs were very mean about anode load resistor ratings and plugging in a 12AT7 instead of a 12AX7 can burn them out. The 12AU7 is even worse. In some cases the alternative valve will not last long e.g. a 12AX7 where the AU7 is needed. The designers KNEW WTF they were doing!

As for valves affecting the "tone" of a guitar amplifier? I have never seen any properly done research about this and from my own limited experience it ain't so. Different OUTPUT valves might sound slightly different but not nearly the "night and day" hyperbole we read.

I mentioned the PI stage? Here greater care should be exercised because not all double triodes have as high a heater cathode voltage rating as the 12AX7 (ECC83) and ad hoc replacement can result in an almighty hum, likely in the middle of your best posed solo! Not all 12AX7s are top quality and few as good as they were 50 years ago.

Dave.
 
rob aylestone said:
That's not what I suggested - they're too expensive to discard if they're fine. If you were paying me to do a tube swap, I'd suggest doing the lot, but if you've determined which one is trouble, and are perfectly happy swapping it - just do that one and save some money. Only you have control over the sound. It's like the tyres on your car - they all wear a little differently. Do you replace ones that are not approaching the legal limit? I don't know about you, but if I see one is worn, or it fails the annual test, I buy one tyre - I do the other one when it needs it. If you have 4, and one is worn out, replacing that one restores the sound. If you hear other issues, then if they are the same type. NOT similar - tubes fall into a number of categories (Dave is the expert here) but some are acceptable alternatives, and sometime just a brand thing, but others have different performance. I remember the old tales that ECC84 could be replaced by a 6N14P - because it had better performance. Something to do with linear vs not linear gain curves, and they were a plug in alternative some swore by, but an ECC84 had different pin connections to an ECC83 - so swapping to different tubes can be risky if you don't understand them!
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Thank you, makes sense.
 
ecc83 said:
My apologies Rob, I was a TAD (boom! Boom!) hasty there!

You make a very good point about "swapping types"? In general...DON'T! Some designs were very mean about anode load resistor ratings and plugging in a 12AT7 instead of a 12AX7 can burn them out. The 12AU7 is even worse. In some cases the alternative valve will not last long e.g. a 12AX7 where the AU7 is needed. The designers KNEW WTF they were doing!

As for valves affecting the "tone" of a guitar amplifier? I have never seen any properly done research about this and from my own limited experience it ain't so. Different OUTPUT valves might sound slightly different but not nearly the "night and day" hyperbole we read.

I mentioned the PI stage? Here greater care should be exercised because not all double triodes have as high a heater cathode voltage rating as the 12AX7 (ECC83) and ad hoc replacement can result in an almighty hum, likely in the middle of your best posed solo! Not all 12AX7s are top quality and few as good as they were 50 years ago.

Dave.
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Thank you for the reply. Some of the technical stuff over my head, but I think I got the important bits.
Good to know it shouldn't screw with tone outside of not minimizing hum as much and things of that nature.
 
gene12586 said:
Thank you for the reply. Some of the technical stuff over my head, but I think I got the important bits.
Good to know it shouldn't screw with tone outside of not minimizing hum as much and things of that nature.
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Where did I get too technical Gene? If you want to understand, tell me and I am sure I can break it down for you.

Dave.
 
When I have replaced tubes in my amps, the power tubes were replaced as matched sets (6V6 or 6L6 as appropriate for the amp). You want the tubes to have similar bias current at idle. When you buy power tubes, you should be able to get a pair with the same reading. The Deluxe Reverb should have a pot for adjusting bias, but if you don't know what you're doing, it's best to have a tech do the job. Lots of lethal voltages there!!!!

Preamp tubes were only replaced when there was a problem, such as going microphonic or failing, and always with the same type. The Deluxe Reverb has both 12AX7 and 12AT7 tubes. They do different jobs in different positions, so matching isn't required here. Like Dave, I don't hear the massive tone changes that you read about on guitar forums. I also don't tend to run amps at full song. The last time I did that was around 1975.

Finally, you have the GZ34 Rectifier tube. IT converts AC to DC. I've had them run for years without a peep.
 
Ah! The Thermionic Rectifier! Yes Rich, they used to be among THE most reliable of valves. Their efficiency (emission) did fall slowly over many years but that only resulted in a small drop in the 'A' HT voltage and a dB or so loss of maximum power, not noticeable in practice...THEN we got the modern versions! Arcy sparky! The b'stards would flash over and blow fuses. They did NOT like standby switches! One brand we found reliable, TAD. Beware GZs with smaller envelopes.

Re "pre amp valve sound"? Forgive me if you have heard this before... I was tasked to build a rig that allowed a guitar signal to be 'hot swapped' between two ECC83s of different brand. The ideal was "source security" (eggs and baskets) but we needed to know if the user would detect a change in the tone of the amp. Yes, different 83 brands did give veeeeery slight differences in tone as detected by two very experienced player/technicians but no [reference was found. The conclusion was that without such a test rig* no one would ever know.

*and mine was the only one in existence AFAIK!

Dave.
 
gene12586 said:
I have a fender deluxe reverb reissue (tube) amplifier. Some months ago I replaced maybe 3-4 of the tubes because they were starting to cause issues - though I no longer remember which ones I replaced. I think I replaced them with the same tube models (though it's possible one of the replacements was a slightly different model). I'm just reading online now in multiple places that when you replace one or more of the tubes you're supposed to replace all of them. Is that really true? That seems a bit ridiculous and too costly. Or is it ok to just replaced one or several at a time?
Thanks.
Click to expand...
Power tubes should be replaced all at once - either a pair or quartet of matched tubes - Preamp can be one at a time or when they are exhibiting some funkiness - @Slouching Raymond is right in that moving around helps sometime - becuase the different position use different parts of the Tube - no remembering which. ones you switched is bad - and not swtching out with the same tube is bad - unless you are looking a for a specific tone.
 
We must consider practicalities, economics and GREENESS! If one of your EL34s arcs over and blows a fuse and you have a spare, plug it in. Check that the hum level is still OK and if so that valve is "near enough for jazz" Certainly good enough for rock n roll! If you had a Radford 25 then of course you would splash out on some top end Telefunkens. Even if the valve is a bit hummy it will get you through the night. DO make sure however that you replace the HT fuse with exactly the same type and value and if it blows a second time, retire the amp for later examination. (make a note to selves...find out what the fuses are and get some in!)

I was once given several sets of EL84 and EL34 "pairs" and "quartets" to check for matching. They weren't. Not really!

It is not that different positions in the amp use different sections of a double triode. More that some stages are 'fussier' than others. The first stage for example needs a valve with low hum and hiss but the same 83 will be perfectly fine as a tone stack driver or PI.

Dave.
 
I have mentioned "fuses" several times in this thread so I thought a bit of info might not go amiss?

In guitar amplifiers you will only usually find two types. Fast and slo-blow (used to be called "anti-surge") Fast just have a wire in them. Slo-blow has a spring on the wire, or some types a 'blob'. Mainly however all fuses are Slo*.

The current rating is, naturally somewhat higher than the continuous current the fuse the fuse carries. The 'fusing' current is higher and a function of both current and time. Fuses do 'tire' and so you might have one fail after many years in an amp. However, examine it carefully, if black as yer'at, get the amp to a tech. If just gone open circuit it is safe to try another of exactly the same rating. Often all will be well and the amp go on working for another 2 years or more. IF it fails next week you have a problem!

Once in a while you will get spurious, 'nuisance' fuse blowing. This can be due to for instance an unusually high local mains voltage (or the guy two doors away on your phase welding go-karts) Sometimes, if a real bind and the kit seems none the worse with a new fuse, it is OK to go up ONE level in fuse rating. 1.25A to 1.6A say but keep listening, looking and smelling! Once in a while a manufacturer will release an update making it official to up a fuse rating because it was found the original was a bit conservative "out in the wild". BUT it must always be a carefully considered move!

A hefty valve amp of my knowing uses a 1 amp FAST anode fuse. This, IMHO Iis a bit daft since the punter is unlikely to have one and musos being gitists will fit whatever they have to hand! Fortunately the amplifier has been around now for over a decade and none have melted to my knowledge!

Dave.
 
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