I had a chance to drop the chassis out of this bird a couple of days ago and I did a little testing. The sound was a little gritty so I measured voltages, tested tubes, and proceeded to install some good glassware from my collection.
V1 was a JJ ECC83 and the rest were Sovtek 12AX7 long plate 12AX7s. One was pretty weak, and they all had dates of 2003 on them.
I installed V1: JJ ECC83, V2: Philips 6681 V3: JAN 12AX7 (Philips ECG) V4: 12AX7 RCA, V5: Mullard ECC83 and V6: 6201 GE 5 Star.
I'm making a pitch for mobile radio tubes like the 6681 and the 6201 5 star, because they're meant to work in the worst kind of service with wacky voltages. They're great stuff if you can get them.
Here's what I found in the way of voltages.
Vp: 484v dc
Vscr: 483v dc
Cathode current 39.2/38.7 (this was after installing a matched pair of Ruby 6L6GCMSTR power tubes in place of the Sovtek 5881 coin base numbers which were about 7ma mismatched. The Super 50 has a neat adjustable bias which works like a charm.
V1 1: 217v 6: 217v
V2 1: 237v 6: 219v
V3 1: 358v 6: 358v
V4 1: 238v 6: 308v
V5 1: 238v 6: 308v
V6 1: 248v 6: 242v
Following David Bock's postings on youtube and his other mod postings on the Super 50 I changed out R33 from 4.7k to 1k to improve the reverb a little and installed an old Accutronics 4AB tank from my Princeton Reverb. There's plenty enough room.
So far, so good. Pics to follow