NC-173 Knobs stuck

[kd1nw]

Hi All,

I've been trying to remove the knobs from a NC-173. I've been using PB Blaster to try and free them up but there are a couple that are giving me trouble. The Main Tuning knob has both set screws removed but wont come off the shaft. The RF Gain set screw refuses to budge at all. I've let the blaster soak in over a few days but no luck. Any advice on another way to get them freed?

Thanks 73
Kevin

[W3GMS]

Kevin,

Can you remove the shaft in which the knob is attached to?  If so, you may be able to put the shaft in a vise and start turning the knob off the shaft.  The shaft may be scored so just take and clean the shaft up when you get the know off.  A lot of time there is a coupler and you can remove the shaft from the coupler in order to remove the shaft and then after that remove the knob.

Joe, W3GMS

[kd1nw]

Thanks Joe, you're right. I'll look at it and see how I can do it that way.

[W3GMS]

Let us all know now it turns out!  Sorry for the pun of "turns out" 

Fun stuff and have fun with the project.

Joe, W3GMS

[kd1nw]

No problem, nothing like a good pun to loosen things up a bit

[W7NGA]

heat is your friend ... a soldering tip can usually do wonders on metal knobs and set screws. Plastic knobs pose a problem of course, but you might not have alternatives if penetrating oil doesn't work.

dan W7NGA
San Juan Island, Wa.

[Pete, WA2CWA]

This has worked for me.
Try to get some light oil on the shaft. Tilt the equipment so the oil runs into the knob. Wrap a wash cloth or anything soft (you don't want to mar the front panel) between the knob and the panel. Tap the end of the knob lightly with a hammer. I generally use a piece of wood between the knob and the hammer. Work the knob back and forth several times. Repeat the process if necessary. Ideally, if you grip the metal shaft with vise grips, or some type of pliers, it prevents stress on the component at the other end of the shaft.

[kd1nw]

Thanks Dan and Pete. I may have to try some heat. Pete, I actually tried exactly what you suggested just a little while ago. It looks like I can't get the shaft out without removing the knob. I removed some good ones to see how it would all come apart. Maybe, I'm not understanding something but it appears it wont work that way. Anyway, I doused the main tuning and rf gain with it face down to let the oil get down there but it didnt loosen even with some light hammering. Ill let it sit overnight give it another try tomorrow! Thanks for all your help everyone.

[K4RT]

This has worked for me.
Try to get some light oil on the shaft. Tilt the equipment so the oil runs into the knob.

Tilting the equipment has worked for me on a rotary switch shaft frozen at the internal bushing in a transmitter.  It took several days and several applications of oil in small amounts before enough soaked into the bushing and I was able to break the shaft free with Channellocks. The bushing is a bit different from set screws, but your PB Blaster may just need time to soak in.

Kevin, I have that receiver and I'm interested in knowing what else you might be doing with the NC-173, e.g. why you are removing the knobs.

73,
Brad

[KA0HCP]

I have an NC-173 and had difficulty with a couple set screws.  The worst had split at could only be taken out with pliers.  I had to drill out the knob hole to a larger diameter in order to grip the screw.  In the end, the knob partially broke.

-Keep applying the penetrating oil.  It appears PB Blaster is highly rated.  Others have recommended patience and success after a week or so on tough screws.

-Heat would be good, but I don't know any way to apply much safely without damaging the knob.  Try a hot air gun, moving the radio to a warmer part of the house, etc.  Any little bit might help the oil penetrate.

good luck!

[W7NGA]

Breaking-free R390A set screws is greatly facilitated by applying heat from a tapered soldering iron tip. I think I finally drilled out a couple of set screws when doing my HRO-50T1 and NC-183 refurbishing. Plastic knobs might be quite difficult to work with. It seems there is always at least one knob per receiver that simply won't respond to anything!

[kd1nw]

   Some success   

The main tuning knob came off today, it seems puuting it face down and getting the blaster in there helped. I let it sit overnight and all day while i was at work. I came home and gave it some light tapping rotating it a bit at a time and it finally came off.

The set screw is like kb4qaa described. It looks like the plastic is around the screw at the top edge. I already started scaping it away a little bit at a time so see. hopefully i wont have to drill it, but ill try some heat before it comes to that. i think my wife has a hot air gun so i can use that if im careful not to get blaster all over it.

Also Brad, I'm trying to get the chassis out of the case. The case it quite rusty but I could strip it and repaint along with some lacquer stick for the letters on the case that are remaining. A few words like MVC and PHONES are basically rusted away. But, Id rather clean it up and keep it from rusting any further if i can.

Thanks again everyone! 73
Kevin

[K4RT]

Kevin,

Great on removing the knob, and thanks for the information. Keep us posted!

73,
Brad

[w3jn]

The most common issue on National tuning knobs is some dumb ham tends to reef down on the setscrews and it spalls the tuning shaft, creating a lip which prevents pulling the knob off.

If the setscrew is loose, get ahold of the inside end of the shaft with a vice grips and hold it stationary, then twist the knob (both directions) while pulling.  Sometimes a fork underneath the knob helps, but be careful not to mar the paint.  Eventually you'll wear off the roughness on the shaft and the knob will come off.

Before you reinstall the knob, smooth the shaft down with a Dremel stone.

[kd1nw]

Thanks for the tip, Ill make sure the shafts are smooth and be sure not overtighten. Im still trying to get the RF Gain off. It's like the plastic has bonded itself to the set screw. Im pretty certain zero blaster has gotten down there and was probably just evaporating. I tried to remove some of the plastic to see if it was blocking the top of the screw but it looks like its bound all the way down the screw. Looks like there might be a replacement knob purchase in my future...

EDIT: btw I do see those marks on the shaft you described under both set screws.. 

[kd1nw]

Success! Now to remove the emblem and I can get it cleaned up. Thanks everyone. I guess I'll continue the progress in a thread in the QSO section later on. But, here's a photo if you can stand to look at it 

73 Kevin

[W3GMS]

Success! Now to remove the emblem and I can get it cleaned up. Thanks everyone. I guess I'll continue the progress in a thread in the QSO section later on. But, here's a photo if you can stand to look at it 

73 Kevin

Looks like a repaint job to me!  I believe the labels are engraved into the panel so they will fill in nicely after you paint the panel.  Just be careful you don't fill in the engraving to much with the paint otherwise you will have no grove left for the white label paint to go in.  I usually start with an etching primer paint on the panel and then go up from there.  If you repaint the panel, you probably will need to do the cabinet as well since I doubt you will be able to match the new panel paint exactly.   Cosmetic restoration takes quite a bit of time but done properly it can be well worth the effort. 

Have fun....

Joe, GMS

[WQ9E]

Joe is right both that the panel is engraved AND you need to not fill it in too heavily.  I really like those National engraved panels because they do make life a lot easier when restoring.  For filling in the engraving after painting I find the lacquer sticks work very well, I think I got mine from Antique Electronic Supply.  Just make sure that the panel paint is well cured before you fill in so you don't create a flaw when wiping after filling with the stick.

While you are inside the NC-173 check to see if there is a capacitor from one of the rectifier plates to ground, if it is there remove it because when it fails it will take out the transformer before the fuse can blow.  These show up in several of the National receivers from this era.

[w3jn]

My caveat on being careful not to mar the paint with the fork was obviously useless advice here 

[kd1nw]

Thanks guys. I'll keep all those tips on my list. It's looks like it will take a bit longer than expected. 3 of the 4 bolts that connect the chassis to the case are basically welded there by the rust. At least I dont have to be gentle on those. I should be able to apply heat and then maybe hit it with freeze spray. If all else fails I guess I could cut and extract. The fun continues  

Oh yeah, it looks like some one has already sprayed this thing at least once before as there are paint runs and little grey paint flecks all over the place including some tubes and the dial plastic.. not sure if i can clean that off. I also found a stamping on the chassis that it went in for service at A & B Electronics in Tonawanada October 1954