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 Post subject: Firestone 4-A-159 restoration
PostPosted: Dec Sun 31, 2017 7:02 pm 
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Joined: May Wed 18, 2011 2:40 am
Posts: 3618
Location: Littleton, MA
This Firestone 4-A-159 “De Luxe Radio” from 1957 is one of a group that must have been the “tough dogs” from some radio repair shop. Every one so far has some unusual problem that’s been difficult to troubleshoot. This one wasn't an exception.

The case and knobs are polystyrene. I made the mistake of soaking the knobs in high-test isopropyl alcohol in an attempt to get off all the grunge. They softened up and their shape was distorted :-( So I’m having to make-do with random pair of knobs.

Restuffing the filter capacitor for the Firestone 4-A-150

The radio is new enough to use ceramic capacitors and good-quality resistors, so all I initially needed to do was to re-stuff the electrolytic filter capacitor.

I like using the 10 mm diameter capacitors. They are easy to fit into the old can. A little J-B Weld epoxy will hold the can back together.

Since this was a PCB-mounted capacitor, I tried routing the negative common lead through a hole drilled next to one of the common pins. This worked out well.

After re-capping, the radio worked only intermittently. I finally noticed that one of the tube socket pins wasn’t soldered to the pad on the printed circuit board.

The tube sockets have a center pin, apparently intended to insert into a mounting hole with a PC pad. But the Firestone printed circuit board wasn’t designed for these sockets. The Arvin manufacturing line fixed the problem by cutting off the center pin with a pair of dikes. But this socket wasn’t clean-cut, and the protuberance prevented the socket from fully seating on the PCB. The pin nearest the bump didn’t fully reach the PCB pad, leading to an intermittent connection.

A few seconds with a pair of dikes to trim the tip, and the socket was ready to be re-mounted.

Since it’s a PC board, it doesn’t have convenient test points for connecting the signal generator for alignment. I soldered a pair of wires on to the appropriate traces.

Of course during all this manipulation of the chassis, the connection to the loop antenna flexed enough to fatigue and break off.

Ready to be reassembled. I’m just getting in the habit of covering the speaker with a square of cardboard while I work on a radio. This one got a few punctures while I worked on it. I repaired them with Sobo fabric glue.

One of the pads lifted while I was re-soldering the socket, so I added a jumper to ensure good contact.

Aargh! I managed to get the ferrite core stuck on the first IF transformer. While trying to get it unstuck, I ended up destroying the IF transformer.

The Sams Photofact doesn’t list any replacement IF transformer part numbers, only the Firestone part number. But they are just ordinary 3/4 inch PC mount 455 KC IF transformers. Perhaps made by Automatic Manufacturing? They have the same injection-molded polystyrene frame as one that I know to have been made by Automatic.

Mark Oppat says he probably has a Meissner or Miller replacement IF transformer that will work, so I’m looking forward to getting it working and aligned.

Steve Byan

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