FlaCharlie
Super Member
Actually, linear power supplies (which use a transformer) can increase DC voltage if they are configured as a voltage doubler. Lots of highly regarded tube amps use this design. Of course a doubler is not needed if the PT secondary puts out enough AC voltage, which can then be rectified and filtered as needed.
It was reported earlier in this thread that measurements taken with a higher voltage PS (13.2v vs 12v) resulted in slightly higher operating voltages at the tubes. So different PS voltages do affect the tube's operating points, but only by a few volts.
The only possible downside is that the increased voltage also pushes, and even slightly exceeds, the voltage rating of the PS capacitors. That said, there don't seem to be a lot of reports of cap failures. I think I found only one or two reports somewhere.
These little preamps (they are not buffers) run the tubes at voltages that are considerably lower than the tube data sheets suggest.
I breadboarded the audio portion of the circuit using a traditional power supply and listened to it at a variety of voltages supplied to the tube, ranging from what you'd get with a stock 12v supply, a 13.2v supply and at a range of considerably higher voltages that were more in line with the data sheets.
Based on this, I can say that the sound is a bit better with a 13.2v supply than with a 12v supply but it was dramatically improved when the tubes are run at significantly higher voltages, which is how most tubes are meant to be operated.
I discussed my breadboarding experiments earlier, see Post 1501 and others. I posted a schematic in Post 1598. Here's a later schematic, which I mentioned but forgot to post:
I got sidetracked on other matters and never did get around to trying it as a buffer but I still might before I tear down the breadboard and build a preamp. It's a decent sounding tube but I found a couple of others I liked more.
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