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Author Topic: Century 21 PTO-Quick and Easy Tuning Restoration  (Read 3410 times)
K4EJQ
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Posts: 101




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« on: May 13, 2012, 07:24:47 AM »

Hello All; The Ten-Tec Century 21  that has been unused for a while is known to have a problem with the grease that was used in manufacturing hardening with age. This causes the PTO tuning to become difficult if not impossible due to slippage of the drive due to the drag caused by the hardening of the grease. Several ideas for resolving the problem appear on various sites on the internet. I was about to implement one of those ideas when I ran into a problem removing the dial. I did not want to force anything to the "breaking point" so I came up with the following procedure.
 
With the power disconnected to the unit, remove the top cover of the transceiver.. Attach a 200 ohm-10 watt resistor to the top cover of the PTO using just thermal grease ( heat sink compound). Do NOT cover the PTO calibrate access hole. A flat sided resistor is preferred to optimize heat transfer. No Extra Holes-Please!! Using stiff solid conductor wire ( No. 12 or No.14 is fine) connect one terminal of this resistor to the ground lug on the mainframe chassis next to the right-rear of the PTO enclosure. Connect the other end to the positive terminal of C1 the large 13000 ufd filter capacitor which is attached to the PC board directly behind the PTO. Position wires to provide maximum contact of the resistors' body with the top of the PTO enclosure keeping the terminals of the resistor from shorting to the PTO enclosure ( ground).

Reinstall the top cover of the transceiver. Reconnect power to the unit. Turn on the unit and let it warm up for several minutes. After a period of a few minutes you should now be able to tune the PTO again. I have used various values of resistance. 200 Ohms should provide adequate heating to soften the grease. If not try a 100 ohm-10 watt resistor. Do NOT use excessive heat-less than 75 ohms-15 watt for the resistor value should be avoided.
As would be expected, the  additional heat in the area of the PTO will cause a slight shift in frequency of the transceiver-the less heat the better. For my use I did not find it necessary to recalibrate the PTO.

Your mileage may vary. This is not a Ten-Tec approved modification. Use at your own risk. Good Luck and keep the Century 21s talking.

Bunky, K4EJQ




 
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NA7U
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Posts: 72


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« Reply #1 on: May 14, 2012, 03:41:28 PM »

I like it!  Cheesy  Sort of like those dipstick heaters they use for cars that live in sub-zero winter climates! HI.
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N4OI
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Posts: 210




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« Reply #2 on: May 16, 2012, 05:34:37 AM »

Just curious if you have tried installing the TenTec PTO rebuild kit?  I bought a C21 with an unmovable PTO, rebuilt it using the kit, and now it tunes as smooth as butter...   

73 ES GOD BLESS U ES URS DE KEN N4OI   Grin
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