--- In [email protected], "tomnevue" <[EMAIL PROTECTED]> wrote: > > I bought a Sinclair Q202G 4 can VHF duplexer. The previous owner > clearly spent a lot of time playing with the variable capacitors. 2 are > totally ruined and I suspect the other 2 are damaged because I can't > get a notch depth below 60db and it's not stable. These are porcelain > (white glass) piston style marked MAV05A30. Can anyone help me with > some replacements or source of supply? Any help is appreciated. Tom > W2MN > Thanks very much for all the replies. I appreciate knowing that the caps are Johanson 5602 hi-Q (1-30pf).
A ham buddy (now elevated to very good ham buddy)gave me 4 5601 caps. These are the same family except slightly longer (shorter thread length) and with solder tabs. I cut off the tabs and lightly filed the burr so the cap will fit in the countersink. All 4 are now back together and I hope that I can get the cans to the "laboratory" this week to see how they tune up. I did pre-set the notch within range using the MFJ antenna analyzer and the cap adjustment is very smooth (like it should be). Now for general information, the nut is just a locking device and the capacitor is screwed into the threaded mounting plate. Also it was pretty easy to find Johanson hi-Q piston caps at 0-10pf which are about 1/4 inch shorter. I was curious to see if this was enough capacitance to resonate the loop at the right frequency, so I temporairly installed one of these. I added a strip of copper to take up the added length. With the 10pf capacitor it resonated well into the Ham band, but I'm sure it wouldn't make it down to the cavity lower spec of 137MHz. So in a pinch, I think the shorter 10pf version would probably useable for 2 meters. Thanks again. Tom
