A15, matched tubes?

Re: A15, matched tubes?

Hi,
it depends
For the same price I would use a matched pair of power amp tubes, but personally I would (at least for the A15) not invest heavily in matched tubes. Using matched triodes for the PI is not needed, you can measure the difference, but for a guitar amp it's not needed.
Regards,
Martin

Re: A15, matched tubes?

That totally depends on what you call "better"
If you want less distortion in the power stage (coming from unsymmetric amplification due to the unmatched power tubes) you should go with matched power tubes. But only when the unmatched tubes are really different (e.g. 35mA at one tube and 45mA at the other tube with the same bias voltage) you would hear a noticable difference, otherwise it's only measurable but hardly hearable.
Regards,
Martin

Re: A15, matched tubes?

Matched tubes is really only useful in Hifi amps. In a guitar amp, there are so many things that make the poweramp more unbalanced than unmatched power tubes. For instance, most components are usually 5% tolerance or worse. Tolerance errors multiply, so the chance of getting both sides of the poweramp matched are very small indeed.

In a typical fixed bias push-pull output stage (like in the A15) there is an inherent imbalance because of negative feedback entering one half of the phase inverter. This is sometimes compensated for (rather crudely) by using different plate resistors on the phase inverter, but it's still quite a big imbalance. Probably much greater than the difference between unmatched tubes.

So even if you do put matched tubes in, it's not certain that would make the poweramp more balanced (it could even become less balanced. since the difference between the tubes could accidentally be compensating for the inherent imbalance).

Now, I wouldn't mix output tubes from different manufacturers or so, but I wouldn't spend extra money for matched tubes.