GEG ATC TRACON Controller reported a situation where they lost all their main radios and had only 2 standby frequencies and no ability to check the UHF frequencies; which resulted in an unsafe ATC environment. The reporter states that this is an ongoing issue since 2022.

Narrative

I was vectoring one aircraft (Aircraft X) for a practice ILS approach under; I had one direct PDT with a descent; and one more flying own nav for a VFR practice approach. When I went to turn Aircraft X to the downwind; they did not respond; I tried again and still no response. Then I tried Aircraft Y and couldn't get a hold of them either. I switched to standbys and was able to get them. Then I did radio check with Aircraft Z on my other frequency and realized all my mains had gone out and I only had standbys for XXX.XX and XXX.XY. I did not have a way to check the UHF frequencies. We have had problems with these frequencies since cutover in 2022 and something needs to be done about making them reliable. They have gone out several times and besides them being completely unreliable; they sound awful and half the time I'm working these positions I have to turn the volume up and cup my own ear in order to hear what pilots are saying. This is an extreme safety issue and it's only a matter of time before the frequencies go out during an emergency or when we have something headed towards a higher MVA.