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

frsimen · 12th Oct 2022, 5:41 pm

I've encountered the warbly sound and instability if the supply voltage has dropped below the level needed for the HF225's voltage regulators, so check that first. Next check that the internal +5V and +8V are correct.

The AGC voltage at pin 16 of the SL6700 should drop as signal levels increase. Your fault may point to something pulling the AGC line down at switch on. C86, Q9, Q10 or Q11 could be the culprits.

Paula

12th Oct 2022, 5:41 pm	#2
frsimen Heptode Join Date: Jan 2011 Location: Croydon, London, UK. Posts: 773	Re: Lowe HF225 fault I've encountered the warbly sound and instability if the supply voltage has dropped below the level needed for the HF225's voltage regulators, so check that first. Next check that the internal +5V and +8V are correct. The AGC voltage at pin 16 of the SL6700 should drop as signal levels increase. Your fault may point to something pulling the AGC line down at switch on. C86, Q9, Q10 or Q11 could be the culprits. Paula