10-08-2016, 09:16 PM
(This post was last modified: 10-08-2016, 09:17 PM by signalman4.
Edit Reason: missed out a word
)
Hi Guys,
Thank you so much for the replies.
Yes Jeffrey, you right - I( now realise that cap droppers wont work in this type of circuit.
Rob T's circuit is of the Coronation Twin, model R786 but the one I have on the bench is just the Twin model R766 and is similar but the component numbering is different.
I've just thought of a bad feature of this design when the set is used on mains - and there are many similar mains /battery portables like this:
If the filament of V2 goes o/c, you can get 100volts or more across C19 (C21A in the R786) which is a 100uF 12 volt electrolyic which will probably go bang!
Also don't pull valves out when it is switched on for the same reason.
I thought it might be a good idea to fit an 8 volt zener diode at the start of the filament chain to clamp any tendency for excess voltage surges doing damage.
There is a rather unusual mechanism where the 2 pin 5 amp plug was used to push the mains/battery switch into the battery position.
That 5A plug has long gone and it is now fitted with a 13 A plug so will need to find a 5A 2 pin plug in the junk box.
Perhaps it would be a good idea to test the radio on batteries to see what other problems there are like THAT capacitor!
Thanks for the good luck wishes pwdrive.
Thank you so much for the replies.
Yes Jeffrey, you right - I( now realise that cap droppers wont work in this type of circuit.
Rob T's circuit is of the Coronation Twin, model R786 but the one I have on the bench is just the Twin model R766 and is similar but the component numbering is different.
I've just thought of a bad feature of this design when the set is used on mains - and there are many similar mains /battery portables like this:
If the filament of V2 goes o/c, you can get 100volts or more across C19 (C21A in the R786) which is a 100uF 12 volt electrolyic which will probably go bang!
Also don't pull valves out when it is switched on for the same reason.
I thought it might be a good idea to fit an 8 volt zener diode at the start of the filament chain to clamp any tendency for excess voltage surges doing damage.
There is a rather unusual mechanism where the 2 pin 5 amp plug was used to push the mains/battery switch into the battery position.
That 5A plug has long gone and it is now fitted with a 13 A plug so will need to find a 5A 2 pin plug in the junk box.
Perhaps it would be a good idea to test the radio on batteries to see what other problems there are like THAT capacitor!
Thanks for the good luck wishes pwdrive.
