I recently wrote on another thread that I was interested in restoring a Ten-tec Century 21 but found it difficult to find one for a reasonable price. A QRZ.com member, I will call him Matt", made me an offer I could not refuse. Matt requested I post a thread so he could follow the progress as this was his first rig. A brief history. This C21 has been stored for 20 years or more at Matt's mom's house. It was thought to have a bad output amplifier. It arrived last Thursday. The following was found on initial inspection. The PTO ( permeability tuned oscillator ) was frozen The power supply was dead The power amplifier was also dead. The power supply was up and running after the 2N3055 transistor on the rear panel was replaced ( $0.95 ). Turning the C21 off causes the +12.8 VDC output of the 2N3055 to drop immediately but the filter capacitor ( C1 ) drops from +23 VDC to about +13 VDC, staying there for a long time. There is no resistor to bleed the charge so it was done manually. The power amplifier is a module which is easy to remove. There are four RF transistors, the input being a pair of Motorola MRF472's and the outputs are a pair of Motorola MRF475's. The 472's were good but both 475's were dead. Bought a pair of MRF475's off eBay ( $20 for the pair including shipping ) but they will not be here until later this week. http://www.ebay.com/itm/272218595985?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT The PTO was the most difficult to tackle. This is a pretty good description of the PTO issues by N5ESE, http://www.n5ese.com/c21_pto.htm Here are the Ten-tec instruction, http://tentecwiki.org/lib/exe/fetch.php?media=pto_rebuild.pdf The bad news is that Ten-tec appears to be in the process of being acquired. http://www.tentec.com/ Doesn't appear to be any way to order parts at present. The PTO rebuild kit was not needed in this case. None of the parts that went bad or are wearing out are part of the kit. In the picture from N5ESE below, http://www.n5ese.com/c21_parts.jpg the Core Drive Rod ( K ) and the Pistol ( L ) had been glued together by the old grease. After removing the old grease, the PTO turned fine. The most worn part was the Wedge ( O ) which is not part of the kit. Spring ( P ) presses pretty hard against that little Wedge which is plastic. PTO alignment went smoothly. There are two coils, L1 and L2 on the same coil form accessed through one hole in the top of the PTO assembly. L1 adjusts frequency, L2 ( the core at the top ) adjusts span. It was pretty easy to get within 1 KHz at 5 MHz and 1 KHz at 5.5 MHz with a counter. Specification is within 5 KHz at both ends of the PTO range. A part that broke is shown in the N5ESE photo below, http://www.n5ese.com/c21_sans_panel.jpg The upper gear seen in the photo was cracked pretty severely. It would have been better to replace it but for now, the part has been plastic welded together with strands of stainless steel wire embedded in the plastic. The receiver portion is now working fine. The PTO has been aligned. The PTO drift after an hour warm up was measured. It started at 5.100069 MHz, drifted up to 5.100101 MHz ( about 32 Hz ) after 10 minutes, stayed there at 20 minutes, dropped down to 5.100095 ( 26 Hz ) at 30 minutes, and 5.100084 ( 15 Hz ) at 45 minutes. It would move down in frequency if either RF/AF volume was increased by 5-8 Hz. More later.