A friend of a friend brought to me a very beat up PL20 to repair. At the moment it has no bass response and the capsule moves around. The foam had obviously deteriorated and needs to be replaced. I should say that I never worked on an RE20 or a PL20 before.
The first issue was trying to open the thing. YouTube has videos and people show how to do it, but basically there’s a small hex screw at the bottom of the top grill.
supposed to use uses a 0.035″ key (confirmed via the Ampex Mailing List). The screw was stripped and neither my 0.035″ or 0.9mm keys would grab onto it. I thought that maybe the screw was seized, so sprayed some WD-40 on it. When you do that, cover the grill with a paper towel or a rag so no WD-40 gets inside. That didn’t help and the key kept slipping.
Removing a stripped set screw that is sunken in its socket is tough. Some people say to use a very small flat head screw driver. I tried with one but I didn’t have a good grip on it. I went to the makers space I’m a member of and found a Pittsburgh Precision tool that had a 0.9mm bit (which I was sure was square, but looking online it says it’s hex). I put the bit into the socket and tapped it lightly so it grabbed into the screw. Then I used a handle to turn it slowly while applying some pressure. The screw came out.
I should really get that Pittsburgh tool thing, it’s cheap and it came in handy. It seems sturdy, too.