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 Post subject: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Wed 07, 2018 11:10 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 9665
Location: Toledo, Ohio
So how exactly does the 2 speed tuning scheme work on the RCA radios? The reason I ask is that both shafts have pulled out of the tuning capacitor on my 7T. I can reinsert both and the larger of the 2 will turn the cap but the smaller shaft will not move it. How exactly does the smaller shaft move the cap?

Also, what the hell is suppose to keep the smaller shaft from pulling out of the larger one?

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 Post subject: Re: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Thu 08, 2018 4:32 am 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4514
Location: Near Brandon, Iowa
Does the inner shaft have a shallow groove (like a ball bearing race) around one end?

If there are no gears visible on the front of the tuning cap, motion between the slow/fast shafts is probably transmitted by three tiny ball bearings located in the above mentioned groove in the inner shaft. The outer shaft has one end rebated for a portion of its length so that the inner shaft with bearings in place can slide in from that end, but can't go any farther (i.e. cannot be pulled out from the "knob end" of the assembly).

Usually these "planetary" two-speed systems have a spring-backed fourth ball bearing that contacts the end of the inner shaft to minimize friction and ensure good mechanical contact between the inner shaft, the planetary bearings, and the outer shaft.


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 Post subject: Re: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Thu 08, 2018 10:02 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 9665
Location: Toledo, Ohio
This is what it looks like. Now I understand that I'm missing a c-clip to keep the larger shaft from coming out but how or what keeps the smaller shaft from coming out? Is there suppose to be some sort of compression lock inside the larger one?

Image

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 Post subject: Re: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Thu 08, 2018 10:46 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4514
Location: Near Brandon, Iowa
The inner shaft first slips into the outer shaft, with the outer sleeve removed. The grooved tip with the tiny ball on its end
will be trapped by the three planetary balls when the inner/outer shaft assembly is inserted into the outer sleeve. The outer sleeve forces the balls into contact with the inner shaft's grooved tip, and the ball end next to the groove will serve as the shaft retainer because when it is in place, the outer sleeve prevents the three ball bearings from moving out enough radially to allow the inner shaft to pull out.

Yes, the outer shaft appears to need a C or E clip retainer.

You should give all these parts a thorough wash in naptha or chlorinated automobile brake parts cleaner, followed by a light oiling. Be careful because when you wash out the old lube, the balls will probably fall out. They can be retained during reassembly by a dab of petroleum jelly on each one. Dirt will cause rough operation or binding.

If you've ever used an air tool, the snap coupler mechanism that allows fast swapping of tools on the air line is very similar to the way this planetary reduction unit is made. The exception is that the outer sleeve on the snap coupler is designed to be movable so that the coupler can be disengaged; on the planetary unit this feature isn't needed.


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 Post subject: Re: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Fri 09, 2018 10:13 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 9665
Location: Toledo, Ohio
Well, that wasn't working. Pushing the smaller into the larger never moved the ball bearings outward. I looked down the inside of the larger and saw what looked like another ball bearing. I removed the 3 outer bearings and sure enough there was a smaller bearing inside the shaft. Any idea if that is suppose to be there? If not I'm at a loss as to how it got inside the large shaft. That smaller bearing was keeping the smaller shaft from reaching the bottom to push out the larger bearings.

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"AC volts and DC volts and little lamps and lities..."


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 Post subject: Re: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Fri 09, 2018 10:55 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4514
Location: Near Brandon, Iowa
Jim Dutridge wrote:
Well, that wasn't working. Pushing the smaller into the larger never moved the ball bearings outward. I looked down the inside of the larger and saw what looked like another ball bearing. I removed the 3 outer bearings and sure enough there was a smaller bearing inside the shaft. Any idea if that is suppose to be there? If not I'm at a loss as to how it got inside the large shaft. That smaller bearing was keeping the smaller shaft from reaching the bottom to push out the larger bearings.

I mentioned this earlier- I think that the fourth bearing is supposed to be there, and is backed by a compression spring. The spring is there to keep the planet balls preloaded against the inner shaft and the outside sleeve so that there is minimal slippage when turning. Without this preload the system probably won't work normally (you would have to push/pull the inner shaft while turning in order to get it to move).

Now that you've got the end ball out, look down the bore and probe for the compression spring with a stiff steel wire. The spring cavity could be packed with rust, dirt, or petrified grease, jamming the end ball bearing and preventing correct reassembly.


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 Post subject: Re: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Sat 10, 2018 12:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 9665
Location: Toledo, Ohio
Yep, there was a spring at the bottom of the large shaft. I managed to pull it out and it doesn't look rusted at all. I have all the parts soaking in mineral spirits at the moment and will reassemble them in the morning. Still need to find the correct size c clip for this.

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KE8GMW
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"AC volts and DC volts and little lamps and lities..."


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 Post subject: Re: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Sat 10, 2018 5:43 am 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4514
Location: Near Brandon, Iowa
Be certain that the inner shaft is fully inserted into the outer shaft such that the three planet balls are retracted before inserting
the shaft pair assembly into the steel outer sleeve. If you attempt to insert the inner shaft into the outer shaft with the steel outer
sleeve already in place, it will not be possible to insert the inner shaft as far as it needs to go because the planet balls cannot
move out far enough to clear the ball end of the inner shaft.


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 Post subject: Re: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Sat 10, 2018 5:54 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Detroit, MI USA
Exactly. You start by installing the spring, then the 4th ball into the outer shaft. Then you put a bit of grease into the 3 holes and install the inner shaft, depressing the already installed 4th ball and spring, just far enough to get the 3 balls into the holes in the outer shaft. Only then can you install the outer shaft into the main bushing/outer sleeve and install the C-clip to hold things together.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Question on the RCA 2 speed tuning scheme
PostPosted: Mar Sun 11, 2018 5:43 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 9665
Location: Toledo, Ohio
After hunting for about an hour I finally located a clip that was suitable and was able to get the two shafts bac together and working like they should. It was the final step before firing up the radio after going thru it.

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Jim
KE8GMW
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"AC volts and DC volts and little lamps and lities..."


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