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Written by: Mark Gilger, WB0IQK

 The following procedures applies to most of the tube PTO’s except the TR3 and early TR4’s.


There are several things that can be done to improve the mechanical operation of the PTO. 

  • The first is to clean up the old, dried up lubricant on the PTO screw drive mechanism.  Denatured Alcohol, or lighter fluid works good for this. Soak a Q-Tip cotton swab with above referenced cleaner and press it against the screw as you turn the PTO dial from one end to the other.  Continue until all of the old lubricant is removed. See the before picture to the left, and the after picture to the right. It’s best not to put any lubrication on the mechanism after cleaning.

  • Clean up the dried up lubricant in the bearing area shown to the left of the picture.  Use Q-Tip and Alcohol as you did in step#1.

  • Clean up the bar above the screw with alcohol.

  • If the PTO dial wobbles, there is an adjustment to the PTO screw mechanism that needs to be made. Use a 1/8 inch Allen wrench.

  • For the ‘C’ line PTO’s, the cover does not need to be removed. There is a hole just below the PTO shaft. Extreme care must be exercised, or component failure will result. The wrench must be inserted strait. If the proper care cannot be assured, the cover should be removed. 

  • An Xcelite 99PS-40BP Allen wrench set has the correct size and works very well for this procedure.



Electrical Stability:

  • Drake recommends that a ground strap be installed on the vertical support bar which rides on the screw mechanism.

  • The best thing I’ve found for this is to use “Desoldering Braid” sold by Radio Shack. The part number is 64-2090.

  • You might also need some solder flux, also sold at Radio Shack, part number 64-021.

  • Use the flux and put a small amount of one side of the vertical support and some more on the frame.

  • Solder the braid to each prepared area.


Electrical Failures:

  • The first problem is to isolate if in fact you do have a PTO problem. There are several ways to determine this.

  • The PTO operates in the 4.9 to 5.5 mhz range. With an external receiver that is capable of receiving in this range, you can listen for the PTO signal.   You will probably need to use a jumper, and run it into the receiver’s antenna input. Use the other end of the jumper and lay it close to the PTO area. If you can hear the PTO, then rotate the PTO dial to change it’s freq. You should hear the PTO change freq.

  • If the PTO does not change frequency, it’s a good bet that the pickup wire that is solder to the coil form has broken loose and needs to be re-soldered. See the “Solder Point” in the attached photo.

  • The other method to determine of the PTO is working is to measure its output with an 0-Scope. A wave form similar to the one shown here should be present. As you turn the PTO dial, you should see the waveform change.

  • Just about any of the components  can fail, but the problems can usually be attributed to one of the following 4 components:

  1. Zener diode 1N714

  2. Silicon diode 1N4148

  3. Transistor 2N5950, 2N3563

  4. Solder point on the PTO coil is broken.

  • With an ohm meter, put the positive lead on one end of the diode and the negative on the other. Note the resistance. When you reverse your leads, you should get a different reading. The diode is probably ok if the readings are different. The same works for the transistors.



In just about all cases, the cover to the PTO will need to removed and the PTO assembly removed from the unit.

  • Remove the PTO assembly by removing the three screws holding it in place.

  • Follow the wires coming out of the bottom of the unit to their termination points and de-solder them.

  • With a screw driver, you will need to reach in on both sides and press down on the clips holding the cover to the support.

  • In some cases you might need to also come in from the bottom and press on the clips from the opposite direction. Its  not the easiest thing to remove.