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I'm preparing to get into a Wurlitzer Model 140 amplifier, and I've found some deviations from the schematic that appear to be part of original construction. The model/serial number plate is missing, but many components are from late 1962. The schematic I have says "starting serial number 25001."
For example, there is a 10uF capacitor attached to the junction of R40 and R41. It connects to a 33k resistor. The 33k resistor connects to the junction of R34 and C13. These components appear to replace the NFB path of R51/C31 and R35 shown on the schematic since these components are not present.
There is a 22k resistor between the pickup input and the 0.1uF coupling capacitor to the first transistor stage which does not appear on the schematic.
R41 and R38 are both 270 Ohm/5W resistors, and there are 1k and 1.5k carbon composition resistors wired in parallel, respectively, with R41 and R38, possibly an attempt to tailor the bias of the output transistors. These extra resistors would bring the 270 Ohm resistors closer to 220 Ohms, the value shown the schematic. (The output transistors themselves have been replaced with SP1271/652085 with 1983 date codes.)
C30 is 0.047uF, not 0.0047uF.
Might anyone have a copy of the schematic that shows the particular version I'm working on? I'm not thrown by the differences, but, considering that this is a VERY early transistor model, if there is an "improved" version, I could certainly implement those improvements in the rebuild. Or perhaps this is the improved version. I've no way of knowing...
For example, there is a 10uF capacitor attached to the junction of R40 and R41. It connects to a 33k resistor. The 33k resistor connects to the junction of R34 and C13. These components appear to replace the NFB path of R51/C31 and R35 shown on the schematic since these components are not present.
There is a 22k resistor between the pickup input and the 0.1uF coupling capacitor to the first transistor stage which does not appear on the schematic.
R41 and R38 are both 270 Ohm/5W resistors, and there are 1k and 1.5k carbon composition resistors wired in parallel, respectively, with R41 and R38, possibly an attempt to tailor the bias of the output transistors. These extra resistors would bring the 270 Ohm resistors closer to 220 Ohms, the value shown the schematic. (The output transistors themselves have been replaced with SP1271/652085 with 1983 date codes.)
C30 is 0.047uF, not 0.0047uF.
Might anyone have a copy of the schematic that shows the particular version I'm working on? I'm not thrown by the differences, but, considering that this is a VERY early transistor model, if there is an "improved" version, I could certainly implement those improvements in the rebuild. Or perhaps this is the improved version. I've no way of knowing...
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