I do not believe the issue with the Ten Tec PTO mechanics is one of wear in
the planetary drive, and I will explain my reason. The drive is made up of
ball bearings, tracking in a bronze race. We've all seen electric motors
with ball and bronze bearings run for years without a problem. An electric
motor will rotate more in a day than a PTO shaft will be turned in twenty
years, and it will do it without noticeable wear.
The real culprit with these PTOs is a combination of using a grease with
poor aging properties, along with the use of a PLASTIC THRUST BEARING CUP.
It is the latter that causes the greatest problem.
The thrust bearing cup keeps pressure on the planetary drive. The friction
between the balls and the shaft/race assembly must always be greater than
the resistance of the return spring and other frictional losses, otherwise
the drive will slip. As the grease thickens, the need for better contact in
the planetary drive assembly is multiplied.
The problem is, the thrust bearing cup is made of plastic, and it is mounted
via two screws in its "ears" which are out of plane with the shaft. This
allows the mounting ears to stress-relieve, and reduce the pressure on the
end of the shaft, and consequently, on the planetary drive. When this
happens, the drive will begin to slip, whether or not the grease has
thickened, but thick grease will magnify the effect.
I recall seeing one bearing cup so deformed that it was necessary to
re-surface it by scrubbing it on a flat emery surface. I've repaired quite
a number of these drives and have never had one fail again.
The drives I've corrected only required cleaning out the grease and removing
one of the washers under each ear of the thrust bearing cup. This restores
the pressure on the ball/race assembly. Removing the PTO is not usually
necessary for this operation.
Phil C. Sr.
k4dpk
----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
To: <tentec@contesting.com>
Sent: Thursday, January 01, 2009 8:06 PM
Subject: Re: [TenTec] Omni C help
> On Thu, 2009-01-01 at 17:46 -0600, John Cox wrote:
>> Hi Jerry
>> I would say that it is probably not the mechanical part of the PTO. If
>> It
>> is the rebuild kit which is a good thing to buy while it is still
>> available
>> will probably not help since it just replaces the grease and wear parts
>> in
>> the drive. I would think that taping on the tuning knob on any Ten-Tec
>> PTO
>> of this type would cause a frequency shift since you are moving the screw
>> drive when you do that. Now if you are really banging on the key when
>> you
>> send that could be another story =:-)
>
> The drive is spring loaded but when the vernier balls and race wear, the
> shaft develops end play and the PTO isn't far from the internal speaker
> that makes noise for side tone while sending CW too.
>
>> I would look for something heat sensitive in the circuitry common to the
>> receive and transmit oscillator frequency generation.
>
> Which is every crystal and the PTO.
>
>> I would see how my
>> Omni C reacts to taping but I blew the final transistors while testing
>> after
>> rebuilding the PTO I accidentally turned the band switch while key down
>> which is a no no. I still had the front panel off and got confused.
>> 73, John
>> KC0YAI
>
> And I know from working on mine that the PTO parts do wear to make it
> loose. Because of the spring loading the PTO sensitivity to vibration
> varies from one end of the band to the other. A really worn PTO will
> slip, more at the low end than the high end of a band. Because the
> spring tension is higher at the low end.
>
> Something else to check is every internal cable, especially those
> supplying power to oscillators. Pins often respond to a bit of motion to
> clean, but stay better with a quarter drop of DeoxIT from Cramolin
> applied to each pin.
>
> 73, Jerry, K0CQ
>
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