Need help Increasing volume on Dutch HEEMAF '59

[twingall1]

Just re-wired this Dutch RTT copper phone from 1959. I think i got the wiring right, converting to BT socket- phone works but is very quiet- both hearing and being heard down the line.
Anyone got any tips on how i might remedy this? could i have wired it incorrectly inside or is it something else?

The second pic shows the wires coming from terminals "a" (red), "S" (yellow), "C2"(blue) [where "a" and "S" are connected] 
These wires then connect as follows to a UK phone cord: red>red, Yellow>yellow, blue>black

Green is ignored




Thanks, any help would be much appreciated!

Tom

[LarryInMichigan]

That phone is Belgian.  There is a wiring diagram for it at: http://telephonecollectors.info/index.php?option=com_docman&task=cat_view&gid=141&Itemid=11.

Larry