[TenTec] Omni C new owner thoughts

[Shawn Upton]

Interesting, nice find on the issues.  Yes, fun rebuilding the PTO... I had to resolder the crystals on that board, which was even more "fun".
I was using my C last week while my Corsair II was having a problem.  Mine has a bit of heating drift though.  Maybe it's time to rebuild the PTO, again (I used lithium grease I think, maybe real grease is better, but regardless, it's made a number of Q's, and still gets the job done). 

Shawn 

    On Friday, April 12, 2024 at 05:31:01 AM EDT, Marinos Markomanolakis M.D. <sv9dru at hotmail.com> wrote:  
 
 Just my first impressions after getting my "new" Omni-C. It was brought from the US, full of all the options and in great shape, as part of an estate sale from OK, thank you Fred (SK) wherever you are !

It is just such a nice rig, unbelievably quiet Rx, THE most pleasant I have ever used. Obviously designed by hams for hams. Too bad we have lost that hobby ideal over time, as a result of consumerism and falling victims of flashing lights, TV screens and useless gadgets in the latest and "greatest" radios.

Besides needing some cleaning of the filter selectivity switches to bring it back to life, I had to deal with 2 issues and would like to share my experience with the group.


  1.
Rebuilding the PTO.
It was working kind of ok to begin with, but with a "gummy" feel to it, which could get a little better with exercise, but a sure sign of its grease drying out. Carefully dismantling the rig to take the PTO out was 2/3 of the work.

  1.
The actual cleaning and regreasing it was very straight forward and fun.
I ended up using the advice from wireless girl at http://www.wirelessgirl.com/Projects/SidebandRigs/TenTecPTOrebuild.html
and not dismantling the PTO beyond what was necessary to completely clean the old grease before reapplying new lubricant.
I believe the critical point is NOT to remove the (H) stop pin ! Especially if you at least you do not have some spare new pins available. From the amount of force you need to exert to it with pliers in order to mobilize it, by the time you have taken it out, it would probably be damaged, and impossible to be reused. And you absolutely can do a perfect job in restoring the PTO without going through that step. Just take your time with isopropyl alcohol and Q-tips.
For regreasing, I used PTFE lubricant, since the lithium one does have a tendency to become sticky over time. I did supplement the PTFE with some amount of white lithium grease around the ball bearings , since it can preserve metal to metal contacts better than PTFE.


  1.
A strange problem showed up when operating in the 40m band ONLY. After 15-30 min of warming up, a 10,55 Mhz "oscillation" appeared in TX even without any mic input. That would appear as a low level "carrier" less than 1W, coexistent with the normal SSB signal. This appeared to raise the SWR seen in the outboard bridge and in the rig's SWR indication, while TX ing in a perfectly tunned antenna.
A lot of scenarios were considered and disproved, but then I observed a strange thing. This "oscillation" would completely disappear when activating the ATT in RX !!!
The ATT board PIN diodes and transistors were checked ok, and finally I decided to check the 9 MHz trap alignment at the front end of the RX.
It was found to be completely off, and after retuning it the problem was completely gone !
So obviously, the 9 Mhz IF signal was getting through the front end and mixing inside the TX circuit to produce the
creeping carrier. It probably only appeared in the 40m band, being filtered out from the BPF of the other bands.


Reassembling the front panel, I replaced the burnt 6V mini -bulb with a 3mm bright white LED (with a 270 Ohm 1/4W resistor in series), and the result is extremely pleasing to the eye, especially in dark or low-level ambient illumination.
It gives a very nice contrast with the display above.

All in all, I am extremely happy with this new radio. I had in the past a Corsair - 1 and a Jupiter, but I like this Omni much better than both.

Hopefully my experience can be of use to anyone servicing their 546 model.

73,
Marinos, sv9dru / ki4gin
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