Hello,
In my 1939 RCA K60 there is an RL-70H-6 loudspeaker. It sounds like total crap.
Reason being is that it's frequency limited. The cone and speaker surround are one in the same, with ridges in the cone to make it more flexible and act as the surround. I'm almost certain this is the reason for the limited bandwidth. I play my mp3s/cds through either the victrola or television input of the radio which sound very bandwidth limited. I hate to destroy the integrity of this beautiful radio, but I feel I'm not getting the full frequency range the amplifier can put out. In my research, I think I have two options:
1. Modify the original loudspeaker by cutting out the surround (which is part of the cone) and gluing in a modern rubber replacement. But where am I going to find one for a 12" speaker? The cone is in decent shape.
2. Buy a new permanent magnet speaker, audio transformer, and field coil. Since the old speaker used the field coil as it's magnet, I need to find a field coil that has the same specs of the old one. I believe a Hammond 155J should do the trick perfectly. It's 15H, so it can store a lot of energy, 300mA max current flow, as the B+ draw is 67mA according to RCA schematics it should be fine, and it's resistance is 1.026k which is within tolerance of the original 1.06K field coil resistance. Hammond makes a "universal" audio transformer which through different pin arrangements you can connect any speaker. RCA schematics say the power output of the amp is 2.5W typical, 4W max.
Any tips or suggestions would be greatly appreciated.
Thanks.
Jonathan