My amp is about as loud as a wart on Lemmy's chin.
What speaker do you have plugged in? If you wire up something really efficient, you'd be AMAZED at how loud even 1W can be.
I'm running it into the 12" speaker of my Roland Bolt 60 tube combo, the speaker is not labelled, but is pretty good.
I got the voltage up to 60 volts last night by adding a couple more stages to the MAX1044, so I got another volume increase - nice! But I've run out of suitable caps to go all the way to 90 volts, I'll pick some up very soon.
I have decided to add two Si diodes between the 12 volt supply and the MAX1044's input to limit the voltage going into the MAX1044 to 10.6 volts, which is just a smidge above it's spec. Better safe than sorry.
I'm also planning to try Ge diodes in the voltage doubling matrix, as they have lower voltage drop that Si - and I have hundreds of them. R.G's Geofex article about the MAX1044 suggests zeners for even less losses - I don't have many, so I'll go with Ge and try to get as close to 90 volts (the 5672's maximum spec) as I can. I think I'll end up with eight stages of voltage increase, so 16 diodes and 16 caps.