[rvt32016]

I see your posting of an article about refurbishing a horseshoe magnet pickup.  I wish I had that 35 years ago when I acquired an Atwater Kent model 75 radio/phonograph.  A radio technician I knew got the chassis working and the radio still sounds great.  The pickup was in terrible shape and all I knew was to try and replicate what I saw.  I found a coil and mashed it slightly in a vise to fit the cavity, replaced the rubber damper and it worked!  I knew nothing about rubber or coil specs.  A couple years ago it was sounding sick (I rarely play it except for fun experiments).  The rubber damper seemed fine, and I used heat sink tubing for the cradle sleeves.  I had always been concerned about the heavy weight of the magnet, and it seemed weak.  I didn't know about using a "keeper" when I removed it for the other repairs.  Then I thought of trying powerful button magnets.  The result was almost ear shattering volume! More experiments and I now use just one little button magnet on each side (the polarity must be right or you won't hear anything, plus the pickup is a lot lighter.  I've tried minute adjustments to the magnet screws and right now the volume and frequency response seem good but there is a little distortion on the loud passages.  I was astounded by how loud it got when the cradle was more loose.  Any suggestions on the distortion?  Really not bad, just noticeable.

[Chas]

I assume the OEM magnet has been removed? If so, there may be distortion because the pickup is no longer as heavy as it was.

Another idea, the signal is too great, try a 20K resistor across the pickup coils. Go lower if there is little or no effect... chas

[Arran]

I would post this on the ARF, there are people on there whom have worked on a number of magnetic pickup phonographs. Part of the problem with heat shrink is it isn't compliant enough, and the older horseshoe magnets tend to get weak with age, it's a common problem with horn and cone speakers of the 1920s. Usually the problem with magnetic pickups is that they don't generate enough voltage, crystal ones put out too much which is why they shunt them with resistors, which often need to be removed when they are replaced with a ceramic cartridge, 3 volts output verses 1 volt. I have heard of rejuvenating the magnet by wrapping a coil around it and applying a DC voltage, but I would look on the ARF for information on this, Doug Houston made some posts on this I think.
Regards
Arran

[rvt32016]

Thanks for the input. Two buttons per side easily provide enough volume. I think the main distortion problem turned out to be some hairline tears in the speaker cone. Repaired with some silicone caulk. Frequency response is excellent. Some slight distortion on extremely loud operatic stuff, but not enough to worry about it. Never thought about not enough weight, so Ill try a record that has some issues and see if that makes a difference. Even without a bass reflex system the bass from this thing is amazing. Unfortunately there is also a moderate 60hz hum. Tubes OK so opened up the chassis and the input transformer looked baked! Some of the bakelite broke off but I taped and repaired some wiring. It had started to burn the paper on the bottom plate so I covered that part in duck tape. There also is a faint buzz when touching the metal tone arm and phono transformer. I did something before that stopped it but have no idea what it was. If anybody has a magic solution that doesn't required electronic knowledge or professional overhaul I'd love to hear it, but for now I'm Ok with it. Still get jaws dropping when I show it off! Ah, fixed the buzz with a new phono wire made from old heavy duty TV antenna lead in and firmly inserted into the connectors. Hum not quite as bad but very faint when the radio is on.

[Arran]

I would scrape the silicone off and use some contact cement instead, silicone makes a lousy cement for speakers, it's too thick, has a habit of peeling off, and looks ugly. I don't know where the idea came from to use silicone to fix speakers, the speaker shops use basically a black tinted version of contact cement, or some other rubber cement, which is usually neoprene based, not silicone based. Silicone is for bathtubs, even fabric glue is preferable.
Regards
Arran