RCA Radiola 18
 

Hi guys,

I just acquired a RCA Radiola 18 that I'd like to get running some-day. There's just a few issues:

the schematics I find do not list capacitor values for the AC model, well...it lists a couple but not all. Does anyone know where I can find a complete schematic.

the other issue is just how was the speaker coupled? was it field coil? was there a dedicated OPT for it?

not unusual for a set of that era to use a high impedance speaker, no output transformer, they often just connected the speaker to the plate of the last tube. If you use a modern speaker you will need to add a transformer to match the impedance and complete the plate circuit. The schematic should show you the speaker arrangement.

Yeah. I found a good schematic. IT basically shows the plate of the AF tube going through a .5uf cap and then to the speaker. So it must have been either a direct high impedance connection or had a small OPT on it.

I'll have to look up what the UX-171 requires for impedance. I may have something.

Typical old hi-z speakers are 2k ohms. You can use the speaker and output transformer from a defunct AA5 radio in place of it. These early sets used wax/paper caps for the power supply filters, and they typically are OK.