[TenTec] PTO Backlash help needed

[Bwana Bob]

Tom:

I found that on my Corsair and Century 22, the felt washer is very 
important for preventing the dial from springing back, especially at the 
edge of the band where spring tension is at maximum.

On both of these rigs there are two felt washers stacked together and 
located between the analog dial skirt and the tuning knob.  To adjust 
the drag, just loosen the tuning knob setscrew, then apply pressure in 
the center of the knob with the thumb while retightening the setscrew.

Have fun!

                                                                   73,

                                                                   Bob 
WB2VUF



Tom NØJMY wrote:
> I'm very leery about celebrating too soon, so with much knocking on 
> wood, I'm just going to report that the felt solution has favorably 
> impressed me thus far.
>
> I doubled over a piece of felt, cut it out, put a hole in it, and then 
> slipped it over the tuning shaft of the one Century 21 which I have not 
> yet disassembled.  Basically, I just stuffed it down in the hole in the 
> front escutcheon, up against the lock washer that holds the dial on.  It 
> does not turn with either the knob or the inner shaft.
>
> Oddly enough, after turning the knob CCW and releasing it, it still 
> visibly jumps back CW, though just a smidgen.  However, listening to 
> c.w. sigs, I am unable to tell any change in frequency.  Holding  on the 
> the knob for a second after stopping seems to eliminate the knob 
> backlash completely.  Incidentally, this is near the full CCW of travel, 
> where there was the most backlash before.
>
> Fixes this simple always scare me, so I'm not quite ready to declare 
> victory yet.  If, however, this unit continues to behave this way, I 
> would say the backlash, even to someone not use to the Century 21's 
> little quirks, is minimal enough as to be more than satisfactory.
>
> I still have three more to go, though, so wish me luck!
>
> 73,
> Tom NØJMY .   .
>
> Hayseed Hamfest Co. - Multi-section Can Capacitors
> for vintage Heathkit, Drake, Halli, Hammy, more...
> www.hayseedhamfest.com
>
> wa3fiy at radioadv.com wrote:
>   
>> Hi Tom.  Welcome.  Good to see you here.  I greatly enjoy your entertaining 
>> and informative posts to GlowBugs.   :-)
>>
>> To your question.  I'm no expert on the matter but I think the unidirectional 
>> backlash is due to a spring being compressed when you turn the tuning 
>> knob CCW.  That spring pressure is pushing back against the "pistol" and 
>> trying to turn the Acme screw thread.  This is a case where you want a little 
>> more friction in the system.  Try loosening the main tuning knob and see if 
>> there is a felt washer or two between the knob and the 0-100 dial plate.  If 
>> not you need one or two, can't recall what TT uses.  Hold slight pressure on 
>> the knob, compressing the felt washer slightly, as you tighten the setscrew.  
>> That will provide some friction between the knob and dial plate which turn at 
>> different rates.  Play with that and see what you get.
>>
>> There is a plastic bearing on the back end of the PTO enclosure which is 
>> spaced from the enclusre by one or more flat washers under the two fixing 
>> screws.  That spacing adjusts spring pressure on the screw thread which in 
>> turn adjusts the pressure on the ball drive.  I sometimes play with that 
>> spacing as well but I think it has more to do with eliminating slippage in the 
>> ball drive than in minimizing backlash.
>>
>> Good luck.  The Century 21 is an interesting rig.  Sort of solid state HW-16, 
>> but not quite.   :-)
>>
>> 73,
>> -Lee-
>> WA3FIY
>>
>>
>>     
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