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ms660 · 24th Dec 2017, 4:53 pm

Ok, the confusion might be that the schematic in the A104 manual shows L19 to be the loudspeaker field coil and R13 is on a dedicated tag strip.

The A104R the r/gram version) shows L19 to be a stand alone choke (not a field coil) and that R13 is fitted between two tags on that choke.

I've never worked on either so far as I can remember, but from the looks of it the A104 went through a production change from field coil loudspeaker to permanent magnet loudspeaker, the manual gives the latter's model number as a A104PM and it also confirms the circuit changes, in that one R13 is shown as 2.7K, that resistor also feeds the screen grid, like it does in the A104R. So for the moment ignore the 10k value that I stated earlier for R13, it's most likely to be 2.7k, the screen connection arrangement will confirm.

Lawrence.

24th Dec 2017, 4:53 pm	#13
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Murphy A104 Ok, the confusion might be that the schematic in the A104 manual shows L19 to be the loudspeaker field coil and R13 is on a dedicated tag strip. The A104R the r/gram version) shows L19 to be a stand alone choke (not a field coil) and that R13 is fitted between two tags on that choke. I've never worked on either so far as I can remember, but from the looks of it the A104 went through a production change from field coil loudspeaker to permanent magnet loudspeaker, the manual gives the latter's model number as a A104PM and it also confirms the circuit changes, in that one R13 is shown as 2.7K, that resistor also feeds the screen grid, like it does in the A104R. So for the moment ignore the 10k value that I stated earlier for R13, it's most likely to be 2.7k, the screen connection arrangement will confirm. Lawrence. Last edited by ms660; 24th Dec 2017 at 5:03 pm.