RCA 6K3 Preliminary Capacitor/Resistor Research - Printable Version
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+--- Thread: RCA 6K3 Preliminary Capacitor/Resistor Research (/showthread.php?tid=26424)
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - glyphmon - 06-15-2026
Tonight's project was cleaning the vernier drive which went reasonably well. With the drive disconnected, however, I tried (carefully) to turn the tuning condenser and I feel like it is stiff for what it should be, which is funny because I don't have much frame of reference in this, so now I have additional questions.
1 - preferences for what to use to relubricate the vernier drive (I have seen fishing reel grease and silicone lithium grease mentioned as options)?
2 - how free-spinning should the rotor be, and what should I use to loosen up the stiffness in it if it is good to do so?
Best wishes,
Roy
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - Arran - 06-15-2026
Roy;
It's likely stiff because the bearings still have the old grease in them, wash that out with a solvent of your choice, then replace with lithium grease, or something similar. It may also be that the rear end of the condenser has the adjustment for the pivot bearing done up too tight, but it's more then likely hard grease.
Regards
Arran
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - glyphmon - 06-15-2026
Arran,
I cleaned the vernier first. It's stiff without the vernier attached at all.
The pivot bearing would be the thing with the flat-head groove at the rear along the axis of rotation? Is that just a simple screwdriver adjustment? Any harm to loosening that? Or is lubrication of some sort a better option?
Best wishes,
Roy
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - morzh - 06-15-2026
Are there ball bearing or just a groove with some pin spring holding it down, and that back screw centering it?
Just spray some lithium grease anywhere you see the point of pressure or friction; see if this loosens it.
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - glyphmon - 06-15-2026
This is the tuning condenser from the side and back-ish. I don't think it has any ball bearings and that slot on the back is pretty darn stiff - doesn't feel like it wants adjusting. I'll pick up some lithium grease tomorrow and see where that gets me.
Best wishes,
Roy
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - morzh - 06-15-2026
Well, it is plain and simple dirty.
Personally I take these apart and give them dish soap bath in the first place. That plus the follow-up lube usually take care of all the moving problems.
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - RodB - 06-16-2026
Roy,
That slot on the back is a screw adjustment to put tension on the shaft of the rotor. The nut tightens to hold the screw in place. Adjustment of this is rarely needed. Mike suggested putting lubrication on the other side where the screw meets the rotor shaft. The front end of the shaft is likely where the bearings are. They probably have old dried up grease causing the stiffness. The rotor should move smoothly throughout it's rotation without much resistance yet not floppy and loose.
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - Arran - 06-16-2026
Roy;
They is no harm in adjusting it, as long as you don't back the thing completely out, only a fraction of a turn is enough, but try spraying WD40 on it first, and then a drop of oil. I think cleaning the cap would be a good idea, you don't have to take it completely apart to clean it, I usually clean those whilst I am washing the rest of the chassis, but the odd one needs more attention, and removal. like a crusty one I found in an Airline AC/DC set where a mouse used the chassis as a urinal.
Regards
Arran
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - glyphmon - 06-16-2026
Arran,
Lithium grease today took care of the resistance. I did try adjusting that screw - it wouldn't budge at all. The vernier is relubricated and reinstalled and now the fine adjustment works just as well as the coarse adjustment. I will do some cleaning before reinstalling the assembly, but there's not much actual dirt/dust, mostly just a patina on the metal.
New rubber supports on order, a few wires to replace that are shedding their insulation, and it can go back together for further testing/alignment. I realized my DMM doesn't have a fine enough setting (AC settings are for 600V and 200V) to measure the AC for doing the alignment so I'm watching a VTVM on Ebay right now. Previous alignment was done just by ear.
Best wishes,
Roy
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - Arran - 06-17-2026
Roy;
It sounds like you solved your problem so adjusting the rear bearing is moot. In case you have to do it in future it's a two tool affair, you need a wrench to loosen the nut, and a flat bladed screwdriver to adjust the cup, the nut is there to lock the cup in place. It's rather like adjusting cone and cup bearings in a bicycle wheel.
Regards
Arran
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - glyphmon - 06-28-2026
Okay, getting into the more esoteric aspects now. I think, as Arran has suggested in another thread, this radio may have fallen over forward at some point in its past. Not only is there weird damage to the middle of some veneer, but Saturday I observed a crack in a piece of trim that would probably have inflicted the force that did it.
I've noticed three things in the chassis that make me think there was some serious trauma:
1 - one of the rivets that holds the tuning condenser to the part that mounts to chassis had popped and was loose - I managed to secure it a little bit with a judicious amount of force from some pliers, but not sure how that will do long-term
2 - the rotor blades are perfectly straight to my eye, BUT they seem to be off-center between the stator blades, as if the entire rotor assembly was jammed a fraction of a millimeter toward the back of the chassis; this was observable when I used some heavier stock paper to brush between them - one side very tight, the other loose by comparison
3 - especially on shortwave, reception on a detectable station is tremendously improved with the application of very slight pressure upward from beneath the tuning knob
Number 1 (loose rivet) doesn't concern me too much here, but Numbers 2 and 3 make me think there's more to be gained if I can straighten the issues out.
Right now, the radio can hear signals or static around 900 MHz and up. Picked up 1360 from Hartford, CT tonight; picked up something from Virginia area I think a couple nights ago. But down in the middle of the dial especially we get just a lot of buzz which varies with the position on the dial - not even what I would call static. Down around 600, we get some crackle, then silence, then crackle and a little buzz once again, so I feel like there's an actual short where that crackle is happening. I feel like if there was an adjustment that could be made to position of the rotor along its axis, that would stand a chance of livening up the AM band. There is more life on shortwave, but still the dead zone surrounded by crackle at the same points on the low end of the dial.
As for the improved reception when applying basically just a light touch from the bottom of the tuning knob, it shouldn't be some electrical conductivity from my finger since it's going through the knob. We're talking going from barely audible to near full volume difference in sound. The only thing I can think of is that even this light touch starts to relieve pressure between the gear on the back end of the vernier assembly and the gear that turns the tuning condenser. Would it be possible that the rotor is also very sensitive to its vertical alignment and may be out of whack at the front "bearing"? I'm not even sure I see how this could come apart to adjust.
On a separate note, I found a really strong shortwave station tonight. I caught the station ident as Radio Republica Cuba and according to shortwave.live, it was on 9490 and broadcasts out of Issoudun, France. I had to actually turn the volume down. Now, my alignment is still woefully off. If this was actually 9490, it was showing around 10500 on the dial. AM similarly, 1370 still coming in at 1400 on the dial. I'm going to try calibrating my signal generator Sunday or Monday which I suspect may help get the alignment closer to where it needs to be. At least the aligning has been consistent so far, even if wrong. Some of the adjustments of the trimmers have been so close to the end of their adjustment range that it's really hard to peak, but I suspect that's because we're really straying off where they should be in the first place.
Best wishes,
Roy
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - MrFixr55 - 06-28-2026
Roy, you may have hit in something (Sorry about the pun). The giveaway is the static that you receive as you rotate the cap. Go back and forth tuning. If you can reproduce the "scratch" at the same dial indication on all bands, there is your smoking gun.
Generally, the spacing between rotor and stator plates of a tuning cap should be consistent except for the end plates which have notches, that allowed sections of these plates to be bent for better tracking. Look at the cap carefully. There may be adjustments for centering the rotor and stator. Some sets have an adjustable bearing on the rear of the cap. Adjusting this may stiffen the cap but may push the rotor plates to a correct position.
Try to flex the tuner itself to see if this changes things. Flex the chassis in an area where the cap is not affected These techniques may help find intermittent operation caused by mechanical issues. You may be looking at multiple issues.
Many times, connections to the chassis are through rivets that may get loose and connect poorly. Good HiFi amps and even one radio in my collection have "Ground Busses", a thick wire where all "returns" are made. This bus connects to the chassis at only one point. Unfortunately, most mass-produced transformer powered sets don't work that way ("Warm chassis" transformer sets do have a "ground Mecca" centered around the 1st Audio tube.
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - glyphmon - 06-29-2026
MrFixr55,
Thanks for the tips. I did manage to adjust the centering with the rear set screw and this cleared up the sound across the band marvelously. But then it was back to being so stiff that the fine tuning knob on the vernier was just slipping like before. So today the dial came apart again to be able to squirt a little bit more lithium grease in the front bearing area, and then did the same by the set screw at the back. Got it back to a place where it could turn with ease and have the rotor blades centered nicely.
In the process, I damaged the shortwave band lamp. So looks like I'll need to pick up a #46 bulb.
I'm sure it goes without saying that adjusting the axial centering of the rotor did a number on the alignment and it's only receiving the local AM station at a very low level. I have a (hopefully) working tube tester on the way, so I'm going to try testing the remaining tubes (just to be have tested them all), calibrate the signal generator, and only then run one more alignment and this should mark the end of the electronic tweaking of this particular chassis.
In a more general vein, I did want to get people's opinion on the possible interference from a nearby transmission line. My house is along a small, regional transmission line running at 43.5 kV. Where I am at inside with the radio(s) is probably 70 feet from the lines at a right angle. What sort of impact would one expect to be experienced from a line at this level, at this proximity?
I'm going to try to put in a dedicated grounding rod and wire for the radio(s) within the next couple weeks, as well as to string the long wire antenna I've got balled up right now along the outside of the building
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - glyphmon - 07-08-2026
Perhaps final update?
Tube tester, an EICO 625, came in, and while yes, I'll need to go through and verify that these components are all within spec, it did work to test (with an observable difference) both the new and replaced tubes. New ones tested positive very quickly. Old ones were much closer to the questionable range and took longer to reach that point, so that seems to make sense given what we've observed for voltages, I think.
I did a calibration on the signal generator which was appreciably off. There was an ESPN affiliate station (880 KHz, I think) that I was able to receive in my truck, so that's what we used. Where was nothing on one of the convenient dial markings on the signal generator. It took a large adjustment to the trimmer to get the generator to where I could get a zero-beat, but I don't think it was egregiously off-frequency. I guess it's just a very fine-adjusting trimmer.
With that done, performed an alignment, now about a week ago, but the power level was way down for some reason I couldn't fathom until I got to the end and tried tuning to different stations. Even my AM transmitter was coming in poorly. Until I switched the input selector to radio mode.
The entire alignment was done based on the audio bleeding over despite being disconnected from the output section. Not sure whether to be impressed or not, but it's one lesson I hope I only need to learn once.#46 bulbs came in today and replaced the one for the shortwave band indicator. With that reinstalled, I did one final alignment with the input switch in the radio position and managed to get a little more oomph out of the various adjustments. The local station, WDEA 1370 still is coming in at just a hair under 1400 on the dial, and there's virtually nothing else that it picked up tonight. 1370 has a weird little variable whine to it, but I know it's not this radio specifically because another analog dial radio I have gets the same thing.
Shortwave is much more active and, though I'm not sure of the frequencies exactly, since no station I've tuned in so far seems to want to identify the frequency it's broadcasting on, I did pick up about three stations with pretty decent clarity. Among them, I think, was another Cuban broadcast and Radio Romanian International again, which conveniently was the short-term goal that got me started in this whole process in the first place.
There is what I think might be described as a small amount of motorboating at the very top end of the shortwave range, but I don't think I'm getting much of anything in that area anyway besides a bunch of high-pitched tones. Those have been pretty consistent since we got this into operating condition, not sure about the motorboating, but I think that's only since lubricating the tuning capacitor the first time.
I did pick up a grounding rod and some bare copper wire for a ground. I know I'll have a bear of getting it down into the ground - there's a lot of scrap granite from quarrying operations everywhere in my yard, including next to the house. Is there an acceptable minimum depth that I could strive for? I'll also be stringing up the antenna outside and we'll see how these two improvements may impact the performance.
Does anyone have any thoughts on the potential from interference from the transmission line nearby? From my last post: My house is along a small, regional transmission line running at 43.5 kV. Where I am at inside with the radio(s) is probably 70 feet from the lines at a right angle. What sort of impact would one expect to be experienced from a line at this level, at this proximity?
Thank you everyone for your assistance in getting to this stage. About to switch fully onto refinishing the cabinet next. At least there will be prettier pictures.
Best wishes,
Roy
RE: RCA 6K3 Preliminary Capacitor/Resistor Research - MrFixr55 - 07-12-2026
Hi Roy,
Great progress!
Yeah, living near a 45KV power line is not great for radio reception, and not great for a lot of things. A lot of environmentalists raise questions about the health effects of radiation. One activist stood under a HV transmission line (Possibly 100KV or 1 Megavolt) with a standard fluorescent tube. The tube glowed. (Hey, if that happens, wind a coil to pick up some free electricity!
I can't remember if the strongest interference is if your inverted L antenna parallels the power line or is perpendicular to it. Use a radio with a loopstick antenna, tune in a desired station and rotate the radio for the loudest signal with the least noise. This is the direction that your Inverted L Antenna should point.
The ground rod ideally should be sunk 8Ft. It is OK of it is not straight down. It can be diagonal or even laid in a ditch horizontally and buried. Moisture is important.