UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - FM tuning drift

Kat Manton · 26th Apr 2007, 3:31 pm

Hi,

I generally expect valve VHF sets with no AFC to drift about a bit after switching on from cold, sometimes for as long as half an hour before settling down once the temperature has stabilised. If your set only drifts for the first ten minutes, I'd consider that to be pretty good.

Given it's capacitively tuned, if this is the usual air-spaced metal plate variable capacitor, I'd expect some drift as this warms up and the metal expands. Perhaps permeability tuning became common on VHF sets for this reason? I find permeability tuned sets drift less, but they still drift.

Admittedly, B&O might've managed to produce a drift-free valve VHF set. It'd take someone else with the same set to confirm or deny whether this is the expected behaviour for this set.

Regards, Kat

26th Apr 2007, 3:31 pm	#2
Kat Manton Retired Dormant Member Join Date: Jul 2005 Location: West Yorkshire, UK. Posts: 1,700	Re: FM tuning drift - any ideas? Hi, I generally expect valve VHF sets with no AFC to drift about a bit after switching on from cold, sometimes for as long as half an hour before settling down once the temperature has stabilised. If your set only drifts for the first ten minutes, I'd consider that to be pretty good. Given it's capacitively tuned, if this is the usual air-spaced metal plate variable capacitor, I'd expect some drift as this warms up and the metal expands. Perhaps permeability tuning became common on VHF sets for this reason? I find permeability tuned sets drift less, but they still drift. Admittedly, B&O might've managed to produce a drift-free valve VHF set. It'd take someone else with the same set to confirm or deny whether this is the expected behaviour for this set. Regards, Kat