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

G6Tanuki · 7th Oct 2019, 7:26 pm

I've got a R606 (not the MB version) here; I've also got a R24 (mains/battery) - the 606 I run off a homebrew mains supply [LM317 regulator) and it's hum-free.

The R24 was hummy on mains when I got it - problem turned out to be that the big smoothing electrolytic in the mains-supply had lost capacitance. A nice new 2200uF 25V electrolytic removed the hum - could be worth checking the smoother in yours?

[remember that the main smoother is _always_ subjected to voltage as long as the radio's plugged into the mains - and when the radio's turned-off at the on-off-volume control the smoother will be unloaded and so charged to the peak-voltage of the AC waveform. Your smoother may have seen 100,000 hours of full voltage over a decade or so...!]

7th Oct 2019, 7:26 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Roberts R606MB I've got a R606 (not the MB version) here; I've also got a R24 (mains/battery) - the 606 I run off a homebrew mains supply [LM317 regulator) and it's hum-free. The R24 was hummy on mains when I got it - problem turned out to be that the big smoothing electrolytic in the mains-supply had lost capacitance. A nice new 2200uF 25V electrolytic removed the hum - could be worth checking the smoother in yours? [remember that the main smoother is _always_ subjected to voltage as long as the radio's plugged into the mains - and when the radio's turned-off at the on-off-volume control the smoother will be unloaded and so charged to the peak-voltage of the AC waveform. Your smoother may have seen 100,000 hours of full voltage over a decade or so...!]