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 Post subject: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 15, 2015 4:59 am 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
I just purchased a 1937 RCA 93A record player. I want to hook it up to my (much later) amp, but first want to ensure that it is working properly, which it currently isn't.

After plugging it in, I turn on the power with the on/off - volume knob at the side, and there is an immediate buzz, a loud one. It diminishes very slightly after I have hand started the turntable, and varies in pitch, giving out two tones, almost grinding sounds. It is difficult to get the turntable going, but once it has started it does run at the correct speed.

I have oiled the shaft and ball bearing at the bottom. If one takes the turntable off, one can look down into the space that the turntable shaft fits into. The top is cup shaped. Looking at a schematic I downloaded it appears there should be a leather washer and then a steel washer up against the underneath of the turntable. Both are missing from my model. From the rather blurry schematic I have it is hard to ascertain what the shape / dimension of these washers are. As a stop gap, I experimented with a rubber washer and a small fender washer. They make no difference whether they are in place or not. i still get the terrible buzz either way.

I am much more of a mechanic than an electrician. Any ideas anyone?


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 15, 2015 6:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17756
Location: Albuquerque, NM 87123
Is the buzz directly from the turntable or through the speaker?

If that turntable uses an idler tire I would imagine the rubber has dried out by now. They can be rebuilt.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 15, 2015 3:17 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4131
Location: Boston, MA USA
No idler -- this turntable has a direct-drive synchronous motor. Make sure the motor windings are firmly secured to the motorboard. If they are loose they can set up a vibration.

-David


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 15, 2015 7:23 pm 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
Thanks for the suggestions.

I have examined the motor windings and they appear to be solidly fixed. The turntable was scraping on the motor board at one point. I increased the distance between the three rubber pads and the turntable by inserting cardboard spacers and also adjusted one of the motor support screws. Now the turntable has no interference.

However, the hum persists, and now the turntable resists being turned by hand, and so will not engage at all. I cleaned the rotor and stator surfaces with a small brush ... all seems to be clean and in good condition.

I am concerned about the lack of the leather washer, washer and shim washers. (Part numbers: 4083, 14230, 14231). Does the leather washer act as an insulator? Could the lack of it be the cause of the hum and the malfunction? I have tried a rubber washer as a temporary fix, just to see if it made a difference. Obviously the rubber would cause too much friction, and slow the turntable dramatically. However, it made no difference, perhaps because it was too thin.

I have downloaded the schematic from Steve Johnson's Antique Radio site, but it does not give a sufficiently detailed illustration of the shaft and washer set up. The brass cup at the top of the stator assembly that receives the shaft looks a little scored, as if it is that portion that is causing the problem, which is why the lack of the leather washer is making me blame that for the problem. Does anyone have any photos / illustrations of the washer, or perhaps, hopefully, a solution?


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 15, 2015 7:24 pm 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
FYI, the buzz is from the turntable. I have not yet hooked it up to an amp and speaker.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Sat 16, 2015 8:40 pm 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
I cleaned the rotor & stator once more, and carefully remounted the turntable. Now it spins very freely without any power, and when powered up turns nicely at 78rpm.

However, it still hums, in two tones. Almost as if it is rubbing somewhere, but I cannot see where. Still bothered about the absence of the washers - would very much like to know the dimensions, and even more, would like to see a detailed exploded view of the washers and the female part of the shaft showing the brass cup at the top.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Sat 16, 2015 9:20 pm 
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Joined: Apr Wed 09, 2008 3:37 am
Posts: 14324
Location: Little Rock, Arkansas
There's such a thing as a bum motor... you may have to replace the motor with another one.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Sun 17, 2015 12:45 am 
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Joined: Dec Mon 12, 2011 3:45 pm
Posts: 284
Location: Georgia
Do you have this information?

http://www.nostalgiaair.org/PagesByMode ... 015726.pdf


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Sun 17, 2015 3:15 am 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
pabilo21 wrote:




Thanks, yes, I do have this info.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Sun 17, 2015 3:19 am 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
Larry Hillis wrote:
There's such a thing as a bum motor... you may have to replace the motor with another one.



That may well be the case. I wonder if it is easier to repair the motor as opposed to finding another one. I would imagine it will be very hard to find another. The motor appears to be two windings.

Unfortunately I am a complete novice when it comes to things electrical. Hopefully I can hook up with someone who actually owns one of these machines, and is conversant with repairing them.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Thu 21, 2015 10:01 pm 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
I have eliminated the hum. I added rubber washers on top of the existing old rubber dampers that connect the rotor to the turntable. Now the turntable turns at 78rpm without any objectionable hum, even when I turn the volume all the way up after running wires from the unit output to the amp. Previous to doing this, I had added small bits of thin card to compensate for the shrinkage of the original rubbers which had resulted in the bottom of the turntable rubbing on the deck of the base. The cardboard raised the turntable sufficiently to make it clear the deck, but with hindsight was the cause of the hum.

However, now i have another problem: as soon as I lower the arm onto the record, the turntable stops rotating. The arm is obviously heavy, but the machine is equally obviously designed to spin the turntable and record whilst tracking the needle.

Any suggestions? The windings do not smell burnt and are not loose but are obviously old. Does it sound like this is where my problem is?


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Thu 21, 2015 10:26 pm 
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Joined: Dec Mon 12, 2011 3:45 pm
Posts: 284
Location: Georgia
Is the motor still rotating when the platter is stalled or are both the motor and platter stopped? Are the pins in the motor shaft correctly seated in the grooves on the underside of the platter?


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Thu 21, 2015 10:38 pm 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
Both platter and motor are stopped. The circlip under the platter is properly secured to the shaft. These were built to be started by hand after power is turned on. They can just as easily be stopped by hand, so there has to be, by definition, a sweet spot where the motor should overcome the resistance applied by the heavy tone arm. As mentioned in earlier posts, I am missing the washers (Spacer, steel and leather) that would normally go under the circlip. I can't get enough detail from the schematic to ascertain their dimensions, or real purpose.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 22, 2015 12:25 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4131
Location: Boston, MA USA
On this turntable the platter IS the motor. This is a synchronous motor which will have very low torque, and as soon as there is enough drag to slow the platter just a little, it will come to a stop.

So you need to minimize the drag. Make sure the stylus is good and the tracking pressure is correct.

If excessive drag is not the problem, I wonder if by raising the platter relative to the windings you might have cut the torque down by raising it too much? Maybe trim the new rubber washers you installed to bring the platter down to ride *just* above the motorboard. It might improve the alignment between the platter (rotor) and windings (stator).

-David


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 22, 2015 1:03 am 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
Thank you David. I think you are setting me on the right track. I will try thinner washers, but fear the result will be that the platter will once again drag on the motor board. I'll work on the tracking. I'm sure the stylus is horrible, but as a temporary fix, can I use a regular steel needle? More to the point is the tracking / weight adjustment. At first I could not see how to do it, but then I see a screw set back close to the tone arm tower. When I look under the tone arm back towards the tower I see a small casting, about an inch in length, at right angles to the tower. There is a spring under it (between it and the motor board) but nothing above it. The screw is currently pretty much all the way in. I am wondering if the spring is should curve around to the top side of this casting, and that this adjusting screw should ride upon it. It that were the case, it would then seem that there would be much more potential adjustment.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 22, 2015 1:18 am 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
Success ... of sorts!

I raised the tone arm by putting a piece of rubber about 1/16" thick upon the casting where I thought a spring should be. This decreased the tone arm weight enough that at least it plays the record without stalling the platter. Can't say it sounds particularly good, but I am using a Medium Tone steel needle, and the platter is really too small for a ten inch record, so the disc 'wobbles' a bit.

Nevertheless, there is progress!


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 22, 2015 2:06 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2579
Location: Haledon NJ USA
A regular steel needle is fine for one play, maybe two if you really want to push it. I use soft-tone steel needles in a similar turntable.

Ken D.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Sat 23, 2015 3:35 am 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
Ken Doyle wrote:
A regular steel needle is fine for one play, maybe two if you really want to push it. I use soft-tone steel needles in a similar turntable.

Ken D.


Yes, you are right. I use them only once. I'd like to get the correct stylus - the one that came with it looks pretty good with a fairly strong magnifying glass. It is oddly shaped - round straight shank where it is housed in the cartridge, and then a bend of 20-30 degrees and at that point the shaft flattens out, and then resumes its round shape towards the tip. It looks like it is designed for multiple plays. Anyone know of a supply?

I have decided to replace all the grommets, and hope that doing so will minimize the hum / vibration even more.

I really appreciate everyone's input - thanks!


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: May Fri 29, 2015 5:32 pm 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
I replaced the grommets. I couldn't find exact replacements but bought larger ones from Antique Electronic Supply and cut them down. Adjusted the tracking weight and plugged in the power and leads out into the amp. Switched it on, gave the platter a push, and Presto! It ran at a good speed, the tone arm tracked well and the sound was, well, not bad! I was playing a Columbia 78 from 1919, so it was acoustically recorded and therefore no really great audio was expected. The platter undulated slightly, so I think I need to make fine adjustments to the motor mount screw. There is still a variable hum, which is more of a vibration than as hum, but it is not as bad as before. I fabricated a leather washer to go on the spindle, but am not really sure whether it has made a difference or not. I had hope that the previous lack of one was the cause of the hum.

If any folk out there have a similar model, I'd love to hear from you.


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 Post subject: Re: RCA Victor 93A Record Player turntable runs noisily
PostPosted: Jul Fri 29, 2016 10:53 pm 
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Joined: May Fri 15, 2015 4:33 am
Posts: 326
Location: Oakland, CA
I returned to this little player a few days ago to see if I could eradicate the hum / vibration. It is a sporadic vibration and not a continual hum. ( I do understand that a hum is basically a vibration). With the power off, the platter spins quietly and smoothly by hand. Upon energizing the motor and giving the platter the obligatory spin by hand to get it going, there is a definite vibration, as if the rotor is catching somewhere. The vibration is tied to revolution, in that the noise occurs each spin. For the life of me I cannot see where it is binding, and given the nature of this motor, I would think that a bind would cause it to stop. The platter is free of the motor board. No scraping there. The motor mounts are new, the spindle is oiled, the bearing is present. I have gone over the surfaces of the stator and rotor with emery paper and a brass brush. Both surfaces are clean, and to the naked eye, burr free.

It would seem that there can only be three places where it can bind. The spindle, the platter to the motor board and the rotor and stator touching each other.
I have read the literature on this model, and there is a definite potential problem with hum, but no mention of a vibration, although one manual does suggest that with a hum present, one solution is placing the unit on a rubber or sponge pad. I have tried that - no difference. It is just loud enough to interfere with playing ancient 78s.

Any ideas?

Bob


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