NC-183D drift

[k7mdo]

Can anyone with experience with an NC-183D give me a thought as to the first place to look to correct for frequency drift?

The set I have was a relatively late manufacture with the late power transformer and the last iteration of schematic.  It plays very well and now has been re-capped and re-resistored (is that a word?).  It does not seem to run hot.

I tried keeping the top open and leaving the bottom off for better ventilation with no success.

It just doesn't stop drifting even after an hour of warm up.  It improves over time but makes SSB reception without riding the dial a near impossibility.

Mixer? Local oscillator? Thoughts, thanks, Tom

[RolandSWL]

Found this:

http://amfone.net/Amforum/index.php?topic=33363.0

Bulletin link at bottom of post.

Roland......

[KM1H]

Ive been using Johnson 160, 189, 193 series of subminiature variables in several brands of equipment since the 60's when I worked at National in the Service Dept.
Dont overlook butterfly caps as one half can be used.
Many of the Johnsons come with shafts, tuning slots, and/or PC mounts so adapting to an old radio is usually relatively simple.

I scour hamfests, on line forums and even Fleabay regularly to keep up with the needs here for my own and customers work.

That Jackson cap in the Fleabay link is too large.

Carl

Carl

[RolandSWL]

Thanks Carl. I've been keeping an eye out for a '183D in good condition. Please tell me that the 'D' doesn't stand for 'Drifty'.

[Steve - K4HX]

What is the "normal" or expected drift on a properly functioning and not modified NC-183D?

[Jim, W5JO]

What is the "normal" or expected drift on a properly functioning and not modified NC-183D?

What is your point of reference Steve?  Drift is dependent on the standard by which it is measured as you know.  The one I have is lucky to be stable on an SSB signal for about 30-45 seconds on the lower bands (D,C). Mine is unmodified.

[KM1H]

Up thru 40M mine barely budged on a SSB signal after about 30 minutes and that was after a full overhaul, selected 6BE6/6BY6's, careful DeOxit D-100 needle injector on tube pins, switch contacts, and variable cap wipers; plus a bucking transformer to bring the AC down to ~110V. The bucker helped a LOT.

I went with a Johnson for B range since I use it often on 10, 12, 15 AM where it was a bit too warbly.

Any remaining excessive drift would likely be requiring a low value 3-4pf  N-750 cap from the variables to ground. Havent done that on a 183D but it helped some other sets including a few old Super Pros and Hallidrifters.

If I were to use it seriously for SSB then crystal controlling the 2nd conversion would be done and likely bracketing a 6C4 under the chassis as the HFO and using the 6BY6 just as a mixer. With a little more time the HFO might become a 6J6 or 12AT7 HFO/Buffer feeding a Pullen connected 6J6 as the mixer which along with some gain redistrubution would solve overload as well as most remaining stability issues. 

[k7mdo]

Well I see I am not alone on this issue.....  this is my 2nd 183D and previously I had a plain 183.  It seemed like the 183 (non-D) was more stable but on the other hand, neither set was ever made for SSB and it really is acceptable on AM for the most part.

I am going to look into the trimmer replacement idea... was hoping that the surgery would not be needed but I recently acquired a bucket full of small air variables in the 1-30 pf range and can probably come up with some to work. 

Thanks for the knowledge on this issue, 73, tom