OK, here's what I measured.
Hum in MP-301 MK2 – measured w/Fluke 123 Scopemeter
Well, it’s very low (see below) which explains why it’s so easily hidden by any program material. Measured at headphone out jack.
A = 1.1 mV
B = 0.9 mV
60 Hz hum (line frequency) that doesn’t vary in amplitude with volume control but there is also some high frequency component which is making it impossible to lock up the time base to verify. The hf component jumps around from 0 to 43 MHZ. Random in nature. I’ll chalk that up to RFI.
My amp doesn’t get abnormally hot for a tube unit. Due to its small size the heat convection gets the rest of the case warm but nothing out of the ordinary or what I would expect. I can keep my hand on the transformer without feeling uncomfortable. Just wish they would put a cage around the tubes as I have curious animals and occasionally kids in the house.
I didn’t take the unit apart but I don’t think tube seating is an issue. They are very snug and a quick check (slight pressure all tubes) with the scope hooked up didn’t change anything.
So, I think my unit is acting pretty normal. Don’t think I can justify tearing it apart for a 1mV hum that only can be heard through my Grado 225si. You might hear it if you use very efficient monitors but my Polks are 89dB sensitivity so it’s never present in my set up.
All that aside, this thing is very easy to listen to for long periods of time. Very smooth and detailed. Again, lacks low end punch but that’s the nature of tubes. The bottom end is nice and rounded with good response, mids are up front and the high end is revealing (at least with the silk dome tweeters in my near fields). Great amp for the price.
