James-Italy ....
I am sure you will go nuts with your Univalve. They are amazing amps.
If you want what is so far, a steal, to make your Univalve do almost everything, I have one tube set on ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1782530048&rd=1 which has no bids yet (I have a $50 reserve on it, but at three times that, these are pretty cool tested tubes), and a few kits at a fixed price of $60 each ( http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1781128780&rd=1 ) that are smaller.
Your powerbrake will work fine with your amp, just realize that you are going to eat up output tubes much faster, and Marshall output transformers don't like to be run flat out for long periods of time. Keep feeling the output transformer of the amp, and if it starts to get hot ... back off.
Keep the impedance matched. If you are going to use a 8 ohm cab, set your amp to 8 ohms, the powerbrake to 8 ohms, etc. Myles,
I've bid on the 10 tube set... at your reserve price... this deal looks like it's MADE for me!
Now I've got to get a similar set of pre-amp tubes... do you have any thing like this?
guitplayer