UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Replacing a 5000 pF capacitor with 4700 pF

David G4EBT · 17th Oct 2019, 9:35 am

If it’s C13, connected via the red wire to T2 - the modulation transformer - it’s stated as 5,000 pf on the circuit. However, 4,700 pf is only 5% below and the original ceramic disc cap won’t have been a precision component - +/- 10% at best. Apart from that, the audio frequency used for modulation of the RF is unimportant and unlikely to be as specified in the manual anyway, due to component variations. If the oscillator section was working before, a 4,700pf cap won’t stop it, and if it wasn’t working before, unless the original cap was faulty (probably not) it’s unlikely to make it burst into life.

If you wanted to retain originality, ceramic disc caps are cheap and plentiful, but if you’re not bothered about that, a tubular mustard cap should be OK.

Hope that helps a bit.

17th Oct 2019, 9:35 am	#5
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Re: Replacing a 5000 pF capacitor with 4700 pF If it’s C13, connected via the red wire to T2 - the modulation transformer - it’s stated as 5,000 pf on the circuit. However, 4,700 pf is only 5% below and the original ceramic disc cap won’t have been a precision component - +/- 10% at best. Apart from that, the audio frequency used for modulation of the RF is unimportant and unlikely to be as specified in the manual anyway, due to component variations. If the oscillator section was working before, a 4,700pf cap won’t stop it, and if it wasn’t working before, unless the original cap was faulty (probably not) it’s unlikely to make it burst into life. If you wanted to retain originality, ceramic disc caps are cheap and plentiful, but if you’re not bothered about that, a tubular mustard cap should be OK. Hope that helps a bit. __________________ David. BVWS Member. G-QRP Club member 1339.