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

Studio263 · 26th Apr 2007, 5:06 pm

Thanks for all your help so quickly!

in answer to some of the questions, the EBF89 diode sections are used as the detector and AGC diode for the AM bands for which the ECH81 is the frequency changer. They could not be used as an FM detector as they share a common cathode.
The ECH81 has been replaced for other reasons (very lazy oscillator that needed 240V mains to start, this is only a 220V set! (now converted), also low gain once working). Could a defective 1st IF stage (as is the function of the ECH81 on FM) cause tuning drift on FM?
I've always considered valve FM sets to be a bit drift-prone too but I can't imagine this being any less annoying when the set was new. Perhaps the Beomaster 900K (all transistor with AFC, available the next season) was designed to address these shortcommings?

26th Apr 2007, 5:06 pm	#6
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,576	Re: FM tuning drift - any ideas? Thanks for all your help so quickly! in answer to some of the questions, the EBF89 diode sections are used as the detector and AGC diode for the AM bands for which the ECH81 is the frequency changer. They could not be used as an FM detector as they share a common cathode. The ECH81 has been replaced for other reasons (very lazy oscillator that needed 240V mains to start, this is only a 220V set! (now converted), also low gain once working). Could a defective 1st IF stage (as is the function of the ECH81 on FM) cause tuning drift on FM? I've always considered valve FM sets to be a bit drift-prone too but I can't imagine this being any less annoying when the set was new. Perhaps the Beomaster 900K (all transistor with AFC, available the next season) was designed to address these shortcommings?