PT and tone?

[daz]

Mercury magnetics, who many love and just as many call snake oil, say that the PT is extremely important to tone. they seem to suggest as much as the PT, or at least close. I'm considering a MM OT, but i'm thinking about whether a MM PT might also be worthwhile. Of course this will make my amp cost me about 3 or 4 hundred bucks more than i already spent building it. Whats the consensus? Is it true or like many say, is true that "voltage is voltage"?

[tubeswell]

The only thing that I can think could make for different tone from a PT is if it had different voltages than the original on the HT winding affecting the B+ throughout the amp, but it would have to be pretty significantly different to be noticeable (I guess like over 20% different). Otherwise you're right - volts is volts

[MWJB]

The PT can affect tone in many ways, as Tubeswell says B+ secondary voltage is perhaps the most important factor (all else being equal) BUT you only really need to have a diffrerence of 20v on the B+ to have an easily recognisable difference in sound. In most amps this is more like a 5% difference in plate voltage, a 20% difference would be unusable, the same model amp for use with 6L6s could have voltages between 380 & 560vdc!!!

Current handling of the B+ secondary and even the 6.3VAC heater windings will have a knock on effect on how stable the voltage is in the amp (when different brands of tubes/different bias settings are applied), as well as internal resistances in the power supply...all of which affects the sound your amp makes.

In short, if you change one PT for another with the SAME ratings & voltages (measured rather than assumed from spec sheets), you are not likely to hear any difference. If you change one PT for another brand, with uprated current handling but the same B+ voltage you may hear some difference. E.g. A Fender Princeton transformer and a Tweed Bassman PT have about the same rated B+ voltage, the lower current handling of the Princeton mean that if you tried to run it in the bassman, actual voltage would drop considerably and the amp would break up straight away. You could switch the other way around, and when rebiasing for instance the B+ would not fluctuate as wildly.

Plus you have typical mass market tolerances - e.g. I've seen from 466vdc to 514vdc on stock 5F6A reissues, with apparently the SAME PT, brand of tubes, biased to tolerance!

The PT is really the heart of the amp. If yours is already easily able to handle the current demands, runs quiet and produces the required B+ then stick with it. I'd only really switch to an esoteric brand if you are specifically after a different B+ & uprated current handling.

[daz]

The PT is really the heart of the amp. If yours is already easily able to handle the current demands, runs quiet and produces the required B+ then stick with it. I'd only really switch to an esoteric brand if you are specifically after a different B+ & uprated current handling.

I think it's pretty stout....250ma/8A heater. Plate voltage may be a little low for EL34's, but that i think is ok at about 410 with a sag R that brought it down from 425.

[MWJB]

Yep, sounds like plenty for a pair of EL34s. I tend to prefer using a reverse polarity zener diode between PT CT & ground to drop B+, for a more "natural" tone (the resistor method often sounds fu8zzy/wheezy to my ear) - a 30v 50W stud mount type would do the job?