[Central-Electronics] CE MM-2 Multiphase RF Analyzer

[Paul Christensen]

I just completed electronic restoration of a gorgeous MM-2 analyzer.  With 
power applied, it blew the 1A line fuse.  I traced it to a Sangamo 0.5uF @ 
1500V paper cap.  The cap looks just like an oil type in a gray, rectangular 
can but in fact it has a paper dielectric according to the Sangamo datasheet 
from the 1950s.  Found a replacement @ 2000V and although it's but taller, 
the mounting dimensions are identical.  Replaced the cap and that took care 
of the fuse problem.   I went on to replace all components as discussed by 
W0YVA in his MM-2 service notes.  Here are some observations.  Without 
having another unit by its side, it's difficult to gauge what's normal and 
what's not.

Issue #1: In manual mode, as intensity starts at full CCW and is gradually 
increased CW, brightness change begins at the left edge of the trace and as 
the control is advanced for more brightness, the rest of the trace starts 
becoming brighter until a point is reached where the control is advanced far 
enough that the entire trace is at the same brightness.  I see no such 
effect in the remaining modes - only Manual.

Issue #2: Trace jitter.  At some sweep settings only in manual mode, I see a 
bit of left-right trace jitter even after changing all the subject caps with 
Polypropylene "yellow jackets."  C17 on the top deck is specified at 0.05 uF 
@ 2500V.  The closest I could find is a Polypropylene film type rated at 0.1 
uF at 2500V.  So, C17 is slightly larger in value but in looking at the 
schematic, the increased C does not seem to affect display performance.  So, 
I'm a bit stumped on the jitter I'm seeing in manual mode.  Of course, it's 
always possible that I ended up with one new cap with excessive leakage but 
that's not a trait I've seen with Polypropylene replacements.  It's also 
possible that what I'm seeing is normal.  I find that I can accelerate my 
ability to troubleshoot by a factor of 10x when I have a working device as a 
reference.  Don’t have that luxury here.

The 6U8 and both 12AT7s were changed as suggested by W0YVA.  A tube change 
did not affect either issue.  Measured voltages mostly agree with the 
schematic and W0YVA's service notes.

Also, looking for a restored CE 20A exciter or a unit that is cosmetically 
excellent but has not been electrically restored.   If you have one 
available, please reply by e-mail.

Many Tnx!

Paul, W9AC