UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Absolute beginner Q's: sensitivity at lower AC input

pcravero · 9th Jan 2018, 11:42 pm

Hello.
I recently acquired a "Radiomarelli RD-160 Amico" AM-only in plastic case, built in 1956 or so. Pictures and diagram can be found online, if interested (schematic diagram). Since it is not "domestic", I will keep my question generic.

Note: this is the first all-valve device I own.

I got it as "non working" in a thrift store for 5€. The volume knob slips and the grip is not enough to turn the shaft in the ON position: could that be the only malfunction?

I built a poor man's AC voltage divider (variometer? variac?) and with a 40W light bulb in series the radio slowly came to life. I measured about 150Vac across the RD-160 AC terminals. BTW, the dimmed bulb looks poetically warmer than usual.

I can tune the upper part of the AM band, while it shuts on the lower: maybe the variable capacitor plates short when most of their surfaces overlap. I need to check that. Nevertheless I can hear the Italian RAI broadcast on 999 kHz: it's pretty loud, but nothing else is picked up. Since it was 19h local, well beyond sunset, the AM band was full of signals for sure.

My question: can the receiver sensitivity be affected by the AC voltage input, like loosing "linearity", or this apparent on-off behavior is caused by something else?

I've had it running this way for 15 minutes, probably too little to trigger other stale problems. I am not confident yet to increase the voltage.

Thanks,
Paolo

PS: dilemma ... follow "if it isn't broken, don't fix it" or "it can be improved"?

9th Jan 2018, 11:42 pm	#1
pcravero Triode Join Date: Aug 2009 Location: Torino, Italy Posts: 47	Absolute beginner Q's: sensitivity at lower AC input Hello. I recently acquired a "Radiomarelli RD-160 Amico" AM-only in plastic case, built in 1956 or so. Pictures and diagram can be found online, if interested (schematic diagram). Since it is not "domestic", I will keep my question generic. Note: this is the first all-valve device I own. I got it as "non working" in a thrift store for 5€. The volume knob slips and the grip is not enough to turn the shaft in the ON position: could that be the only malfunction? I built a poor man's AC voltage divider (variometer? variac?) and with a 40W light bulb in series the radio slowly came to life. I measured about 150Vac across the RD-160 AC terminals. BTW, the dimmed bulb looks poetically warmer than usual. I can tune the upper part of the AM band, while it shuts on the lower: maybe the variable capacitor plates short when most of their surfaces overlap. I need to check that. Nevertheless I can hear the Italian RAI broadcast on 999 kHz: it's pretty loud, but nothing else is picked up. Since it was 19h local, well beyond sunset, the AM band was full of signals for sure. My question: can the receiver sensitivity be affected by the AC voltage input, like loosing "linearity", or this apparent on-off behavior is caused by something else? I've had it running this way for 15 minutes, probably too little to trigger other stale problems. I am not confident yet to increase the voltage. Thanks, Paolo PS: dilemma ... follow "if it isn't broken, don't fix it" or "it can be improved"?