STC TRF Radio no audio - UK Vintage Radio Repair and Restoration Discussion Forum

grahamsmith · 7th Mar 2023, 9:19 pm

hi.

i have a stc radio a trf it has a #47 valve output valve a #80 -#235 and 3 224 valves i get the normal speaker hum to know it is on but i cannot get any audio from speaker just dead stressed out don't know where next .
any help with it.no noise with signal generator.

thanks graham.

Silicon · 7th Mar 2023, 10:53 pm

One way to narrow down the fault is to start at the output stage and work towards the aerial.

If you touch the control grid connection of the type 47 output valve with a screwdriver you should hear a scratching noise or increased hum from the speaker.

If you can introduce an audio signal to the grid via an isolating capacitor you can check the audio quality.

7th Mar 2023, 9:19 pm	#1
grahamsmith Diode Join Date: Mar 2023 Location: Brisbane, Queensland, Australia. Posts: 1	STC TRF Radio no audio hi. i have a stc radio a trf it has a #47 valve output valve a #80 -#235 and 3 224 valves i get the normal speaker hum to know it is on but i cannot get any audio from speaker just dead stressed out don't know where next . any help with it.no noise with signal generator. thanks graham.

7th Mar 2023, 10:53 pm	#2
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	Re: STC TRF Radio no audio One way to narrow down the fault is to start at the output stage and work towards the aerial. If you touch the control grid connection of the type 47 output valve with a screwdriver you should hear a scratching noise or increased hum from the speaker. If you can introduce an audio signal to the grid via an isolating capacitor you can check the audio quality.