Horseshoe Pickup Rebuilding

[Syl]

Remove the top screw AND the thumbscrew.

Pull the cover up toward the front where the stylus cradle is.

Be careful, there is a copper spring (small flat piece about 1 inch by half an inch) on the arch of the magnet to keep it secured with the cover on.



Carefully unsolder the coil's wires from the cartridge connectors. Remove the magnet and both nuts then gently pull up the assembly.



Keep the magnet in a steel tray (or use a keeper; a small steel flat bar, across the magnet poles to keep its magnetization.



Seen from the back, the cradle damper and centering adjustment.

That rubber piece must be replaced.



Carefully remove both brass screws and disassemble the cartridge's transducer. Careful with that coil !



This is the needle cradle. I already replace the dried rubber dampers with silicone sleeves. I make my own by buying silicone rubber bands. They are the right thickness. Otherwise, using silicone caulking and spreading a very thin layer on a mica or other non sticky material. Once fully cured, cut strips and use as dampers. This is the only place this sort of material can be used. Silicone is not the best damping material, but in this case we can use the self lubricating properties of the silicone to offer less friction to the cradle and offer some damping. The frequency response will be enhanced slightly in the highs. NEVER use a rubber band here or a glob of silicone. We need the cradle to freely move without any free play. Too tight and you'll lose up to

50% of output and a poor frequency response.

The freer the cradle, the better the frequency response. Too much free play and the cartridge will distort and destroy the records in no time. Less friction on the cradle with proper damping (from the centering damper on the back) also means a better high frequency response.



The main damper is rebuilt using good man made rubber (very soft). I laminate two pieces for correct thickness and two side by side. The cradle pole piece will sit right in between. Use contact cement or other pliable glue. If you can find a single piece of soft man made rubber (natural rubber will dry and become hard faster) then cut it to fit the assembly then cut a slice right in the middle lenghtwise almost all the way through.



Carefully reassemble the transducer. Fit the coil. The wires should come out the back of the stylus cradle (opposite where the thumbscrew installs).



Install the needle cradle. Note where the wires come out.

Install the pole pice in the centering damper.



Install the second half and loose fit the brass screw (both brass screw should be loose fit for later adjustment).



This is what it should look like from the back.



Install a small card stock piece to isolate the wire from the transducer's body.



Now, for the first adjustment. Both brass screws from the centering plate should be loose enough to allow both halves to move. Squeeze both halves until they barely touch the cradle (seen on the left). There should be no pressure on the cradle but just enough to keep it from -wiggling- excessively. In one word, no excessive play. Secure both nuts but not too thight for now as the cradle should be centered once the metal cover is reinstalled.



Now, centering the pole piece is easy. Hold the needle cradle with one end and center the pole piece in the transducer by moving the brass plate. Tighten both brass screws when done.



Connect the amplifier wires to the back connector and rub a finger on the needle cradle to verify there is output.



Put the metal cover on (without the magnet if you wish) and verify that the cradle is centerd. If not, remove cover, loosen the both nuts, move slightly, resecure the nuts, put back the cover....You get the idea...

Once the cradle is properly centered, put a drop of nail polish on the nuts. If all is well, put the magnet back (if you haven't already), double check if the pole piece is still centered, reinstall the brass spring on the magnet arch. Secure the cover, install a new needle and test.

It is difficult to explain how much the magnet should pull, but a healthy magnet should give a good pull and not be easily removed when put on a steel keeper or container.

If the magnet is too weak, output will suffer. There are outfits and even how-to for remagnetizing magnets which involves a high power electromagnet.

Verify the coil's DC resistance from the manufacturers data.

Coil should be within 20% of the published specs. Coils can be rewound, if you have patience and access to 40 gauge wire.

[philco phan]

thank you syl!
i just tried this on a steinite 102a radio/phono. before,very little output at the speaker-after-much much more audio. now to figure out what the phono's volume control resitance should be,there is a 70k pot there and obviously not the original,any ideas?
phil

[Syl]

philco phan Wrote:thank you syl!
i just tried this on a steinite 102a radio/phono. before,very little output at the speaker-after-much much more audio. now to figure out what the phono's volume control resitance should be,there is a 70k pot there and obviously not the original,any ideas?
phil

Hard to tell. I suspect you do not have a schematic available?

There are two types of horseshoe reproducers. Low (8 to 20ohms) and high impedance. (>1000ohms).

I suspect anything around 1K for low impedance and >10K for the higher version. Not that it would matter much
though. If the volume control does it's job properly keep it as is.

I found a way (many years ago) to restore the horseshoe magnets the easy way and permanently, adding even more
output. I was able to get a solid 3V with that trick. Maybe I should update this lesson.

Syl

[philco phan]

howdy syl,the 102aschematic only shows the radio so no phono info available.
it has a hi-impedence coil,2.4k.output is audible but not room-filling,i think i'll try subbing pots and listen for improvement,could even be miswired,who knows?
the pickup coil is wired to each end of the pot,does that sound right?
radio works very well,lots of volume.
phil

[Syl]

philco phan Wrote:howdy syl,the 102aschematic only shows the radio so no phono info available.
it has a hi-impedence coil,2.4k.output is audible but not room-filling,i think i'll try subbing pots and listen for improvement,could even be miswired,who knows?
the pickup coil is wired to each end of the pot,does that sound right?
radio works very well,lots of volume.
phil

Wiring as you desribe it sounds OK.

Low output may very well be caused by a weak magnet. A healthy magnet should give a good firm pull when sat
on a steel plate. Hard to describe what is right though.

Syl

[philco phan]

the magnet is pretty strong,is there a way to measure output across the coil?
phil

[Syl]

philco phan Wrote:the magnet is pretty strong,is there a way to measure output across the coil?
phil

Using a 'scope and a good record. Average should be around 6-8VPP.

Syl

[Doug Houston]

The pickup shown in the directions is the one for a Victor RE-45. This pickup has an impedance of 200 Ohms, and a DC resistance of about 85 ohms. I've rebuilt quite a few of them, and if the coil needs to be rewound, they're just a ton of fun! The original coil, shown in the pictures, was molded into a soft wax block, which did make it easier to handle, and to install in the pole pieces. If you can rewind the coil with a slightly smaller gage wire, you can add a few extra turns, and get more wallop from the pickup.

While I agree that the magnet should have good pull, it's often not a good indicator of its charge. If it's possible to either make a chatging rig of some sort, or have someone with an industrial charger, always try to charge the magnet at rebuild. I have a Brunswick Panatrope, where the magnet seemed to have enough charge, but the phonograph just didn't have enough suds. I sent it to a friend in Baltimore, who has a real killer of a charger, and he charged it for me. I was amazed at ow much this thing puts out now. My little chatging rig works good, but when it's done on a good magnetizer, it's awesome.

A lot of the pickups, especially in the earlier pickups (Victor Electrolas in the 1925-28 models, used a high impedance pickup that's a real religion killer to rewind. You have to rewind them with #47 wire, and you can't even SEE the stuff. If you're successful doing it, you're a nervous wreck for the rest of the day.