PI mods in Princeton Clone - Stress to PT?

[Martin Beer]

I have a home built amp which uses the aa1164 Princeton schematic (except for a 40/20/20/20uF filter can, Hammond Deluxe OT and an Eminence/Fender 12" speaker). At gigs, I typically run the amp turned up about halfway, where it overdrives slightly with the harder struck notes and is clean-ish when I play lightly. I get usable volume this way and I like the character of the breakup, but just a touch more headroom wouldn't go amiss.
I've seen a few posts recommending the Stokes mod (moving the PI plate supply up to the next step in the B+ chain), and other posts suggesting that this may stress the power transformer unduly. I am using a Hammond PT rated for 81ma at 330-0-330v. My plate voltage is at 408v and I'm running EH 6V6 valves, currently biased at 22ma. Would I be foolish to try moving the PI supply up a step?

[txstrat]

Since you say that you like the sound of the amp as is (i.e. breakup point, clean sound etc.), I wouldn't do anything to the circuit.
Even a slightly bigger OT would barley be noticed headroom wise but would change the dynamics at the same volume level.
I'd add another speaker cab (maybe with the same speaker), which gives you more headroom without losing the amps overall sound.

[Martin Beer]

Certainly, the amp is OK as it is. I was thinking that I might try the mod, and if it changes the sound in a way I don't like, I could put it back again easily enough. Though it would only be worthwhile if I was confident of not killing my transformer.

[txstrat]

Well, actually the Hammond replacement transformer for the princeton is @81ma and a bazillion amps of this kind run on this amperage.
The tubes won't draw more max current than what's in the spec sheet just because of a different PI. You might go ahead.

[Martin Beer]

I've seen a few posts on various forums claiming that this mod might increase the current draw when the amp is played loud by driving the 6v6s harder, and that Princeton PTs are pretty marginally rated to start with. Though there are also plenty of people who have done it without experiencing any problems, and perhaps the 81ma rating of the Hammond allows me some leeway compared to the 70ma Fender PTs. If no-one is saying "Don't do it!", I think I'll give it a try and see whether I like the results. If I don't like it, it'll go back to stock.

[txstrat]

When you look at the tube specs sheet of 6V6 you'll find they can draw up to 92mA a pair depending on the voltage plus the current draw from the preamp tubes would be too much for my taste.
I usually use a PT with 140mA from a German supplier for 6V6 based amps. But I'm over anxious and like to be on the save side - that's why I wrote about the Hammond transformers and the bazillion amps they run in.
Again, if you just need a little more headroom, I'd use a second cab.