Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Nov Wed 25, 2020 1:08 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 20 posts ] 
Author Message
 Post subject: Replacing cartridge in an RCA U-10
PostPosted: Dec Wed 04, 2019 4:40 am 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
I'd like to actually replace the cartridge in my RCA U10 phonograph
with a ceramic one that has less than the current 73 grams stylus force.
The U10 is used as the audio for a TT-5 TV ... its the "correct" gizmo for this,
as its the right age and actually has an input labelled "television".

Replacing is not problem, I can buy suitable ones ... except for the force.

All the ones I can buy need 8 grams. Without the current pot metal cartridge
the force is 28 grams. Thus I need to get rid of perhaps 40 grams total,
including the new cartridge. I should add that I rebuilt the current cartridge and
it does work.

A picture is at https://www.radiomuseum.org/r/rca_u_10_rc_418b.html

A better picture of the same arm is at
https://www.radiomuseum.org/r/rca_r100_ ... _atta.html

Now if I had the R-100 I could simply add a counterweight at the back of the arm,
as there is plenty of room. But in the U10 there is only about 1.5 inches.
It would take quite a bit of lead to get enough torque, and that might break the
bakelite arm.

I could try a spring. I have tried a spring pushing the arm up and it might work OK,
or it might be unstable.

Has anybody succeeded in compensating one of these heavy arms?


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Wed 04, 2019 5:24 pm 
Member

Joined: Nov Wed 27, 2013 5:59 am
Posts: 726
Location: Metzger Oregon
If the arm is truly Bakelite, you might be able to use a trick I tried with a Motorola changer with a metal arm. I dripped solder into the back end of the tone arm, real solder with lead, as that was the most dense material I could get. That worked great, but I just needed to remove a few grams. Bakelite should not be harmed by the heat of melted solder, but test a small area first to be sure!


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Wed 04, 2019 9:44 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
Even Tungsten or Uranium or Osmium is not heavy enough for the space available in this arm.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Thu 05, 2019 3:41 pm 
Member

Joined: Aug Sun 23, 2015 6:01 pm
Posts: 1155
Location: NJ 08090
I've never had any luck trying to tame these monster weight arms. My solution is to avoid these, as they just don't adapt easily to any tracking weight mods, unless you get lucky. Just my $ .02.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Thu 05, 2019 5:44 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
I tried drilling a small hole in the back of my arm last night, and
adding a 6/32 rod out the back, with washers on it. It seemed
to work just fine for reducing pressure, and the arm was still stable,
though I didn;t try playing a record.

OF course, it might not be stable enough for a real cartridge.

What I worry about is cracking the bakelite of the back of the arm.

In real use the weight would have to be lead.

Time will tell.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Thu 05, 2019 6:25 pm 
Member

Joined: Mar Wed 18, 2009 10:22 pm
Posts: 245
Location: Houston, Texas
If you are pleased with the results in weight reduction and plan to keep using the rod and washers, you can reinforce the inside of the tonearm around the hole you drilled with epoxy cement. This will stabilize and strengthen the area where the counterweight interacts with the bakelite.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Fri 06, 2019 8:36 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
Robert Caston wrote:
If you are pleased with the results in weight reduction and plan to keep using the rod and washers, you can reinforce the inside of the tonearm around the hole you drilled with epoxy cement. This will stabilize and strengthen the area where the counterweight interacts with the bakelite.


Excellent idea!


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Fri 06, 2019 8:46 pm 
Member
User avatar

Joined: Apr Mon 15, 2019 9:54 pm
Posts: 277
Location: San Francisco, CA
dtvmcdonald wrote:
I'd like to actually replace the cartridge in my RCA U10 phonograph
with a ceramic one that has less than the current 73 grams stylus force.
The U10 is used as the audio for a TT-5 TV ... its the "correct" gizmo for this,
as its the right age and actually has an input labelled "television".

Replacing is not problem, I can buy suitable ones ... except for the force.

All the ones I can buy need 8 grams. Without the current pot metal cartridge
the force is 28 grams. Thus I need to get rid of perhaps 40 grams total,
including the new cartridge. I should add that I rebuilt the current cartridge and
it does work.

A picture is at https://www.radiomuseum.org/r/rca_u_10_rc_418b.html

A better picture of the same arm is at
https://www.radiomuseum.org/r/rca_r100_ ... _atta.html

Now if I had the R-100 I could simply add a counterweight at the back of the arm,
as there is plenty of room. But in the U10 there is only about 1.5 inches.
It would take quite a bit of lead to get enough torque, and that might break the
bakelite arm.

I could try a spring. I have tried a spring pushing the arm up and it might work OK,
or it might be unstable.

Has anybody succeeded in compensating one of these heavy arms?


Haha! You are probably right about the 73g tracking force on that old tone arm! :lol: I've retrofitted ceramic cartridges in place of the old crystal cartridges on a few record players now. On my 78 rpm RCA RP-178 player from '49 I reduced the tracking force by counterweighting the tone arm using stick on automotive lead wheel weights. These weights work great because they have good mass for their size and the 3M tape will stick forever since it's designed for harsh automotive environment. :) A lot of the old tone arms have plenty of space to attach these weights behind the pivot.

_________________
My collection: https://www.radiomuseum.org/collection/ ... ickel.html


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Sat 07, 2019 3:23 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
I still don't have the new cartridge yet, but last night I tried the suggestion
about reinforcing the arm for a counterweight.

I got a long 6/32 rod and a washer for it that would touch the sides of
the back of the arm making a good way to hold epoxy in place.
I coated the rod with some grease and put a piece of 1/8 inch shrink-tubing on it
(unshrunk). I then assembled the arm, rod, washer, and a nut. I chocked it up so
the rod pointed in the right direction and the washer was perpendicular to it.
I then fill the necessary space with a thick epoxy. After it set hard, about 30 minutes,
I unscrewed the rod. The glue worked nicely.

The back of the arm is not flat and would not hold a nut properly. So I covered
the back with Saran wrap and dolloped some slightly set epoxy on in a blob.
After 20 minutes I removed it from the arm and Saran wrap. I let it sit overnight.

The hole in the arm had made a small depression, telling me where to drill
the hole, which I did (by hand, using a drill in a loose chuck). I then used
a file to shape the sides and back of the blob so a nut on the rod fit nice and flush.

This makes a nice sturdy rod mount. Thanks for the suggestion.


Last edited by dtvmcdonald on Dec Tue 10, 2019 4:37 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Sat 07, 2019 4:40 pm 
Member

Joined: Mar Wed 18, 2009 10:22 pm
Posts: 245
Location: Houston, Texas
Glad it worked out for you. I use epoxy fairly regularly for repairing cracks in bakelite cases. It is very useful in many situations I run into when restoring or repairing vintage record players.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Mon 09, 2019 4:12 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
Last night I tried using the arm and my "restuffed" crystal pickup (using a piezo plastic element)
with the counterweight. I was amazed that it tracked fine at 24 grams or even 16 grams
(on soft passages). Yet the original force was 70 grams!

At 16 grams I played two whole 12 inch sides with almost no sign of steel stylus wear. The
stylus still had a mostly round tip. At 70 grams that would produce a chisel.

Still awaiting the modern ceramic pickup.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Mon 09, 2019 4:47 pm 
Member

Joined: Mar Wed 18, 2009 10:22 pm
Posts: 245
Location: Houston, Texas
Please post some pictures of your work. It would be very interesting.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Mon 09, 2019 5:15 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
Robert Caston wrote:
Please post some pictures of your work. It would be very interesting.


I will. The counterweight I'm using is a kludge of loose random washers. I'll neaten it up and
then take pictures.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Tue 10, 2019 4:13 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
Last night the cartridge(s) arrived. I used the higher output one.

Its mounting is wrong ... the holes are too close together. The instructions
recognize this and strongly suggest kludges.

Machining would be better but our "student" machine shop (VERY well equipped!)
is currently unmanned. So I kludged. Photos tomorrow. Its actually quite sturdy and
a couple of drops of super glue would make it even stronger and still removable.

It took a little bit of filing and bending of the bracket to get it at the right angle, as
there were two tiny tabs in the way of a proper flat mounting.

It weighs very little, like a couple of grams. The cartridge itself, which plugs in,
is 0.5 gram, the rest is mostly in the hardware used for the kludge. I set
the force at 7.8 grams. With the way I held in the weights adjusting was
hit and miss so it took several tries.

It works nicely, and tracks reliably. It even tracked and played a
record warped by 1/4 inch. Interestingly, I have one record without leadin or
leadout grooves ... the area where they would be is nice and flat. So I checked
skating, and there was none.

At that tracking weight, the acoustic noise from the pickup is way down from what
it was at 70 grams.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Tue 10, 2019 11:20 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
Here are photos. Note that the whole arm just pulls out.

download/file.php?mode=view&id=280875

download/file.php?mode=view&id=280876

download/file.php?mode=view&id=280877

download/file.php?mode=view&id=280878

download/file.php?mode=view&id=280879


Attachments:
_MG_9461.jpg
_MG_9461.jpg [ 251.35 KiB | Viewed 2039 times ]
_MG_9465.jpg
_MG_9465.jpg [ 265.41 KiB | Viewed 2039 times ]
_MG_9466.jpg
_MG_9466.jpg [ 231.92 KiB | Viewed 2039 times ]
_MG_9467.jpg
_MG_9467.jpg [ 236.84 KiB | Viewed 2039 times ]
_MG_9468.jpg
_MG_9468.jpg [ 234.53 KiB | Viewed 2039 times ]
Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Wed 11, 2019 4:13 am 
Member

Joined: Mar Wed 18, 2009 10:22 pm
Posts: 245
Location: Houston, Texas
Cool solution. I have an attachment unit with that exact tonearm. It is a beast.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Thu 12, 2019 7:24 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
Last night I got a big shipment of 78 RPM disks from 78rpm.com. These were leftovers from their auctions
and were mostly random 12 inch operatic aria ones, all in great looking shape. Dates from 1912 to 1949.

They sounded as great as possible with a single 6F6 and 5 inch speaker. They had remarkably low
noise.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Thu 12, 2019 9:43 pm 
Member
User avatar

Joined: Apr Mon 15, 2019 9:54 pm
Posts: 277
Location: San Francisco, CA
Yup, that's the same green cartridge that I put in my RP-178 player, with 3.0 mil sapphire needle. I had lots of room to counterweight the tone arm underneath, but looks like yours was very compact. I was able to lower my tracking weight to around 11g and still get the mechanical trip mechanism to trip at end of record.

_________________
My collection: https://www.radiomuseum.org/collection/ ... ickel.html


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Sat 14, 2019 8:27 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1620
Location: Champaign IL 61822
Now a question! How long does the new cartridge's needle last?

A steel needle at 70 grams lasts about 1 or two minutes before
being seriously worn. At about 18 grams it lasted about 10 minutes.

The current needle is a 3 mil sapphire running at about 7.5 grams.
After playing about 2 hours it shows no wear.

Diamonds are said to last 1000 hours at 2 grams, but they are elliptical
0.7 mil. On the flip sides filled shellac is harder than vinyl.

So is there some sort of rule of thumb? I didn't find one easily on the web.

Nobody sells these cheap plug-in cartridges with 78 RPM diamond stylii,
though they do for 33-1/3 rpm mono ones.


Top
 Profile  
 
 Post subject: Re: Replacing cartridge in an RCA U-10
PostPosted: Dec Sun 15, 2019 12:14 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2480
Location: Haledon NJ USA
I would expect somewhere around 50 hours of good playing time from a 3 mil sapphire stylus playing 78s at that tracking force.

That's the problem with sapphire plug-in cartridges, when the tip wears out you have to buy a new cartridge.


Top
 Profile  
 
Post New Topic Post Reply  [ 20 posts ]  Moderator: Alan Voorhees

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 8 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB