Ten-tec Century 21 restoration

Don't fool around with trying to run solvent down the shaft. It won't get down inside the guts of the PTO where the real problem lies. Spend the time and effort to service the PTO properly. It's a bit fiddly but not all that difficult. I've serviced many of them over the years. To do the job, I recommend you have on hand a quart bottle of 91% Isopropyl Alcohol (available cheap at any pharmacy, including Walmart), a roll of paper towels, a cotton terry towel that you won't mind ruining (to use as a work surface), some cotton-tipped swabs, a small plastic tub to soak and clean the parts in, and some hand tools (especially needle-nosed pliers and pointy tweezers). Put about an inch of alcohol in the plastic tub and drop the parts in it as you remove them. Soaking them in the alcohol will help remvoe the old dried-up grease and crud. If you need the genuine Ten Tec PTO rebuild instructions, email me at my_call_sign at qsl dot net and I'll email you a PDF copy. Read it thoroughly, several times, and become intimately familiar with it before you start the job. It will go much easier that way. Refer to the diagram early and often.

Earlier this evening, I serviced a spare PTO that I pulled some time back from a parted-out Triton IV. The job took me about 2 hours total time. Bench-tested and working fine. Sealed up in a plastic baggie until needed later.

 

Great info. Tnx.. I did notice that after it warmed up for a couple hours it started working. Makes sense. A bit of heat helped it seems.

 

There is one thing as I remember. I started to take it apart and could not budge the allen screw on the big knob. Or maybe I didn't have one that fit so I gave up a year or so back.. hmmm

 

The allen set screw on the main tuning knob is .050. On mine, now sold, if the push nut on the main tuning dial was too tight it would cause the dial to slip a bit. hth
73,
Rob

 

I have a C21 that needed a PTO rebuild- that came out nicely. The 2nd issue was no power out. I replaced the finals (and drivers as I already had them in stock). The new finals are 2SC1969's as in a Ten Tec app note. They are apparently a more robust transistor. The drivers are now 2SC2314 as per same note.
So I set bias at 6mA for the drivers. I now have a whopping 0.6W out. Drive power to the input is the correct at 31dBm.This is a pretty simple P.A. and even under a magnifier I cannot see any issues. I will say, the copper etching is quite crude- but it obviously worked at some point.
I have bypassed the LPF's and looked directly at the PA output with an SA- same at around 0.6W.

Any thoughts?

Tnx,
Dale W4OP

 

Dale -
Well that is a Puzzle. Hopefully none of those parts were Counterfeits (China sources).
—
The Sanyo 2SC2314 (TO-126), Silicon epitaxial planar, was a common driver
formerly used in Citizens Band radios. 1.0 to 1.8 Watts output at 30 MHz is typical
https://www.radiomods.co.nz/transistors/2sc2314.pdf

Electronics Surplus (Cleveland, OH) has 2SC2314 (unknown mfg.) in stock, $3.00
https://www.electronicsurplus.com/f-2sc2314-transistor-npn-p-n-2sc2314
===
The Mitsubishi 2SC1969 NPN Epitaxial Planar Type RF transistor has WildWest prices ($6.00 to $30.00 each), failure rates (counterfeit device) common even with $30.00 units.
A Florida reseller via Amazon (Wildfire Electronics) has recent feedback of bad 2SC1969 devices.

Mitsubishi 2SC1969 datasheet
https://www.rfparts.com/fileuploader/download/download/?d=0&file=custom/upload/File-1376528421.pdf

Merit at RF Parts still has an inventory of original Mitsubishi 2SC1969 for $16.95
https://www.rfparts.com/rftransistors/transistor-2sc/transistor-2sc-1000-1999/2sc1969.html

 

How did you conclude there was anything wrong with the existing finals? In roughly 1/3 of no output situations, I have found broken traces and bad solder joints but the devices were fine.

 

While we're on the subject of Century 21 restoration. . . If anybody is parting out a Century 21, I need either the complete 80358 Mixer Board or just coil ass'y T-4 that's located on the Mixer Board. My rig's T-4 suffered an unfortunate accident and got smashed into oblivion. I now have no 40m transmit!

 

There are people selling boards on eBay regularly for the C21. If I don't see what I need, I send them an email asking if they have any other parts. About 50% of the time they have the part and will do a "buy it now" for me. Just did that with some terminal strips I needed for a different restoration.

 

Yep, I've been watching eBay, and all of the other internet trading posts. Eventually I'll find what I need.