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Matched pairs vs matched quad

StepheK

StepheK

AK Subscriber
Subscriber
Curious what people's thoughts are on this for a fixed bias PP amp. I can see the argument that a pair of tubes used in one channel of a push pull amp it might be best if they are a matched pair, but is there really a need for all 4 tubes to be matched? Obviously on this type of amp the bias is adjustable on each tube.

My initial thought has always been "Have the pairs matched but left/right don't need to be".
 
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I agree in general but you wouldn't want the two pairs to be too mismatched I expect. I have a stereo PP 300b amp, a Cary, and it has a common bias adjustment for all 4 tubes so in this case a matched quad is important. I wouldn't design an amp this way. I have plans to split the channels so matched pairs will then be ok. The layout makes it hard to do individual bias.
 
I've always bought matched pairs or single ended amps and matched quads for PP amps with fixed bias with an adjustment for each tube.
It doesn't cost much more. I know I really don't need to though.
For my PPP mono blocks there is only one trim pots for each pair of tubes on each amp. So you do need to start with a matched quad, or two matched pairs per amp.
 
StepheK said:
Curious what people's thoughts are on this for a fixed bias PP amp. I can see the argument that a pair of tubes used in one channel of a push pull amp it might be best if they are a matched pair, but is there really a need for all 4 tubes to be matched? Obviously on this type of amp the bias is adjustable on each tube.

My initial thought has always been "Have the pairs matched but left/right don't need to be".
Click to expand...
Matching each side in a PP amp is important. Buying a matched quad is not more expensive then bying 2 pairs but you get the benefit of having matched pair left even if 2 tubes will be lost. And you don't have to keep them positioned if removed as they all are identical.
 
StepheK said:
Curious what people's thoughts are on this for a fixed bias PP amp. I can see the argument that a pair of tubes used in one channel of a push pull amp it might be best if they are a matched pair, but is there really a need for all 4 tubes to be matched? Obviously on this type of amp the bias is adjustable on each tube.

My initial thought has always been "Have the pairs matched but left/right don't need to be".
Click to expand...
I've found that the placement of the speakers and the "matching of those speakers" to each other has more effect on the stereo imaging than the balance of the amp's output.

Placement and room acoustics. :thumbsup:
 
I've used matched, even triode matched sets of driver tubes, and unmatched. I have yet to notice any difference between the channels.
I'm sure it's measurable, but even when I've used mismatched used driver tubes I didn't notice one channel had a lower volume level compared to the other.
 
Lavane said:
I've used matched, even triode matched sets of driver tubes, and unmatched. I have yet to notice any difference between the channels.
I'm sure it's measurable, but even when I've used mismatched used driver tubes I didn't notice one channel had a lower volume level compared to the other.
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When I test the tubes after a month or two of use, they are rarely "matched." Like in the range of <5% of each other.

Keep in mind that tubes can wear at different rates.
 
Mr Boochie said:
When I test the tubes after a month or two of use, they are rarely "matched." Like in the range of <5% of each other.

Keep in mind that tubes can wear at different rates.
Click to expand...
Very true. With matched tubes your hoping they age about the same. More important with cathode biased amps though.
 
I am skeptical that matching is ever all that important. Our brain is unable to hear asymmetry of phase in music. If the tube amplifying the positive section of the signal of the right side is 10% different than the negative phase it won‘t have any impact that we can discern. This was really important when tubes were used to amplify signals to be read on an oscilloscope or for reference CRT broadcast equipment. But audio?

There is a type of tube audio lover that takes an engineering approach to amps and playback. In their mind there Is a correct representation of the signal/music and any possible deviation is incorrect. Never mind that tubes are the wrong things to be using if “accuracy” is your goal. There will always be some slop in the performance of tube amplifiers. There are wider variations that are deemed good sounding than the engineering mindset wants to admit. It may be the slop that makes us love how our amps sound and why the precision of solid state is less appealing. Shrug.
 
isaacc7@cox. said:
It may be the slop that makes us love how our amps sound and why the precision of solid state is less appealing. Shrug.
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I judge the overall sound's imaging and depth. Badly placed speakers, for instance, have poor stereo imaging and lack precise presence.

It's like a out of focused photograph.
 
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