Hi, I recently found an AWA Radiola model C73 TRF receiver from 1930. It is housed in a wooden box with a hinged lid to access the valves. The set has a mains power supply built into the wooden box but used an external speaker. The radio has five valves, an F203 audio output, x3 224, and an 80 rectifier valve in the power supply. Would anyone know where I might find a circuit diagram for this set? I found this early set in a second hand shop and purchased it as the shop owner was about to throw out the chassis inside and install an mp3 player inside the wooden cabinet. I don,t think they realised the age and rarity of this set. Luckily I purchased this set intime while it was still complete except for the external speaker. I have a photo of an AWA external speaker box from 1930 which I am going to try to reproduce to sit on top of this receiver. Any assistance would be greatly appreciated. This is my first TRF set I have found.

the shop owner was about to throw out the chassis inside and install an mp3 player inside the wooden cabinet

Well done on saving it from the "re-purposing" vandalism.

Radiomuseum doesn't have a schematic, only a drawing of the radio. That's an attractive box:

http://www.radiomuseum.org/r/amalgamate_radiola_45_ch_c73.html.

It's not on Kevin Chant's site either.

You may have to draw out the circuit by hand. It shouldn't be too complicated.

Thanks for your help GTC . I also checked the Australian Official Radio Service Manuals that are in the reference section of the Hobart State Library but they do not go back to 1930. I mainly wanted to know the voltages the power supply and the valves operate at, as well as the impedanceof the external speaker and field winding so I can try to find a suitable external speaker. I read in a newspaper advertisement from 1930 that this set could be used with either a magnetic speaker, or a moving coil speaker which would have been quite an expensive addition in 1930.

Can't see anything in what I have; Only TRF with 24's I have worked on was a Series 70 Lyric. Chassis in it was 22Kg and the speaker (Rice-Kellogg) was around 8Kg as it had the audio transformer two chokes & it's electrodynamic (Electromagnet: Not permanent magnet)

Circuit may not be that complex. The audio might be transformer coupled, one 24 may be a plate detector, with grid leak that is cactus. Such things can be reverse engineered. 24 is a 2.5V heater RF Tetrode

24 is a heater valve from 1929. They will take 250V and the Lyric used one for a rectifier to get near -84V for the grid of the 50 if it has 450VDC on its plate.

Reference is made to F203 on Radio Museum. Similar to UX245 (45) European base is not the same as UX4 (80 is UX4). One might have to look at the Lyric as they (Philips) are quoting -68V on the 45 grid with a plate voltage of 275 and 4600 (say 5K) load. So it may be resistive coupled, or have a rectifier like the lyric for the grid volts?

It is also 2.5V but is an AC filament tube, likely on its own centre tapped winding, with no cathode resistor.

If you build / rebuild the PSU you can use a resistor for the choke. Volts AC out of the transformer needed. and it needs to be safe to plug in, to get those AC volts with the rectifier removed.

Judging by the volts, do not measure across the small pins of the 80 socket. That might be over 1KV and most modern DV meters won't hack that.

Marc