# Tubes and double wattage amps



## GuyB (May 2, 2008)

When you have an amp that can be used in 15W or 50W (like my Traynor YCS50), there is only one power tube working in the 15W mode. So, if it's always the same tube that is working, it will not last as long as the other one. What can this do on the tone or on the overall functionning of both power tubes (bias, longevity, can you hear the difference when a tube is much "older" then the other) ? And when the tube that is working solo will die (before the other one), will it be preferable to change both tubes, even if one of them could still be usable ?


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## gtrguy (Jul 6, 2006)

Usually a low power mode puts the power tubes into a different operating mode- Triode versus normal Pentode... in a two tube amp it doesn't normally 'turn off' one of the tubes so differential wear isn't an issue...

gtrguy


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## Andy (Sep 23, 2007)

Exactly what gtrguy said. 

I highly doubt that there would be only one tube in use on the lower power mode, unless you were told that by the manual, or a Yorkville employee who knows their stuff. It would be a huge design flaw IMO to use only one tube -- even with the auto-biasing circuit.


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## Adicted to Tubes (Mar 5, 2006)

The Traynor does indeed switch to a single tube,cathode biased in the low power mode.Not that hard to accomplish with solid state parts.Working on it is another story!
If you were to play in the low power mode all the time,I would suggest switching the power tubes once in a while to keep them fresh.Kind of like rotating the tires on your car.
They simply use a PC board to contain the parts necessary to make one tube shut off and re-route the other tube's cathode to a resistor/capacitor that makes it single ended class A.

www.claramps.com


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## GuyB (May 2, 2008)

Thanks for answering, but I'm a bit mixed up here ! Two of you say that it does not operate with only one tube and one says that it does ! I went back to the manual and that is what they say :

«Amp Mode 
The YCS amplifiers can be operated in two different modes, full-power class AB and low-power class A. When operating in full-power mode, the full voltage is applied to the output and preamp tubes and the amplifier operates in a traditional class AB configuration. Selecting the low-power mode cuts the operating voltage by half and increases the bias in the output tubes to full class A operation. This allows the output and preamp to operate with a great deal of more ‘saturation.’ Operating in Low Power mode also results in extended tube life.»

I have read somewhere in these forums that a real class A works whith only one tube. But here, when the manual says : "...increases the bias in the output tubes to full class A operation" it seems that they are talking about the two tube*S*.

And, btw, the YCS is not auto-biasing. I'm still perplexed !


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## Budda (May 29, 2007)

i'd call/email yorkville and ask


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## Wild Bill (May 3, 2006)

GuyB said:


> Thanks for answering, but I'm a bit mixed up here ! Two of you say that it does not operate with only one tube and one says that it does ! I went back to the manual and that is what they say :
> 
> 
> 
> ...


The number of tubes has NOTHING to do with the class of operation! If the plate voltage and idle current is right then the tube is in a certain class of operation. It doesn't know or care if there are other tubes in the circuit in the same class.

I think perhaps some folks got confused with push-pull, which ALWAYS has to have a pair or pairs of tubes feeding opposite sides of a push-pull output transformer! Push-pull can still be in class A, ABx or whatever. I have a couple of commercial push-pull class A amps in my junkbox. It was also extremely common with home hifi equipment.

You can also run more than one tube in parallel, with all of them in the same class. In fact, with a simple parallel circuit it would be impossible to have them running in different classes!

:food-smiley-004:


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## Balou (Apr 1, 2008)

Wild Bill said:


> The number of tubes has NOTHING to do with the class of operation! If the plate voltage and idle current is right then the tube is in a certain class of operation. It doesn't know or care if there are other tubes in the circuit in the same class.
> 
> I think perhaps some folks got confused with push-pull, which ALWAYS has to have a pair or pairs of tubes feeding opposite sides of a push-pull output transformer! Push-pull can still be in class A, ABx or whatever. I have a couple of commercial push-pull class A amps in my junkbox. It was also extremely common with home hifi equipment.
> 
> ...


I think that we have 2 situations here. The first is that you can cut power by a certain factor by removing one tube working in parallel with an another and in second you want to run in class A.
In the first case, the plate voltage is the same with one or 2 tubes in parallel or not. So each tube see the same power dissipation when in action. Then the tube you had kepted in place work ardly that the one you have removed, so the one you have removed are some backup tubes if you see what i mean. And it is there where the big difference is.
To work in class A you can have all your tubes in place, and just modify the idle current of each tube to work in class A. And then each tubes see the same power dissipation and there is no difference in the tubes life.
Hope that help! (Wild Bill help if i'am wrong, thanks)


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## Adicted to Tubes (Mar 5, 2006)

You have to lower the plate voltage significantly in order achieve true class A operation.So going from a 50 watt push-pull to 15 watts class A,two things have to occur.
1) the plate voltage has to be reduced significantly
2) the current has to go up.
So to do that,it involves a pretty complicated circuit.You can't just pop in a resistor to lower plate voltage that much,because it would create excessive heat.So they likely have an extra tap on the power transformer.Then you have to have bias circuitry that changes the current or bias setting in that mode.Again,the concept is easy to imagine.
A switch that has one voltage tap and one bias circuit for full power and another voltage tap and bias circuit for 15 watt class A.Actually easier than shutting off one tube altogether.
With a PC circuit it is all possible in a small area.This actually makes more sense than my first guess,because this way you don't worry about an output transformer impedance mismatch.

www.claramps.com


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## Wild Bill (May 3, 2006)

Balou said:


> I think that we have 2 situations here. The first is that you can cut power by a certain factor by removing one tube working in parallel with an another and in second you want to run in class A.
> In the first case, the plate voltage is the same with one or 2 tubes in parallel or not. So each tube see the same power dissipation when in action. Then the tube you had kepted in place work ardly that the one you have removed, so the one you have removed are some backup tubes if you see what i mean. And it is there where the big difference is.
> To work in class A you can have all your tubes in place, and just modify the idle current of each tube to work in class A. And then each tubes see the same power dissipation and there is no difference in the tubes life.
> Hope that help! (Wild Bill help if i'am wrong, thanks)


Balou, running tubes in parallel is a rare thing, at least as a single pair. The more common push-pull amp is not parallel. Each tube works on half of the wave cycle and things are combined in the output transformer. If you have a 50 watt pair of tubes in push-pull you can put two more tubes in parallel with each half of the original pair to double the power capability.

Very rarely do you see more tubes in parallel NOT in push-pull! It's just too inefficient. As Addicted to Tubes pointed out, you have to run at much lower plate voltages to be in Class A without burning up the tubes. 

Traynor went to a form of electronic regulation with many of their new amps. This does two things. One is it lets you use a very small "girly man" style standby switch, which I guess they feel is more "cute" than the big ass old switch that we have seen for years and years! The other is that it becomes very easy to switch the voltage down if you want to run in Class A. Or you can do like A2T suggested and take your B+ differently from the rectifier to get half-voltage. How doesn't matter as long as the voltages are reduced properly.

Notice that from the Traynor description and from looking at their schematic, the tubes are still being run in push-pull and not parallel even at low power. The operating voltages including the bias are lowered and changed to run in Class A. 

This factors are also the reason why you can get 50 watts with two tubes in Class AB1 but one tube in Class A only gets you 15 watts and not half, or 25. You get much more from tubes in push-pull than in parallel. Less distortion in the same class of operation, too.

Just FYI.

:food-smiley-004:


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## GuyB (May 2, 2008)

Thanks fellows. I don't fully understand all of the technical aspects mentionned here but it gives me a good overall understanding of what I was looking for.
And, just to mention, I'm still "learning" and experimenting with my new YCS50 and I was recently practicing/jamming with friends in a small room - a (loud !) drummer, a (loud !) bassist, another guitarist and singer and me with my Traynor YCS50. I was on the dirty channel, gain and volume at about 2-3 o'clock (no boost) and the master volume just under halfway. I had no problem cutting throught the mix even if I was in the 15W mode ! I left it in this mode in the afternoon after practicing at home and forgot to put it back in the 50W mode for the practice !


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