Hi
Thanks for your replies, the problem is if you look at S3, a DSDP switch (or change over switch) intended I believe to switch from resistance measurement to capacitor measurement, you will see that the 2 central common terminals have been bridged together. There are 2 other wires, one from R3 R2 R1 common and one from the switch itself which are soldered together. I cant work out how these would have been fitted to the switch.
I would have thought that for resistance measurement the vibrator, which incidentally is working, would have been switched out of circuit as DC is all that is required. At the moment S3 seems to not do much, there is a slight change in the vibrator when it is changed over from R to C.
A similar thing had been done with S1 which was faulty, it had been rewired and the 2 common terminals had been also bridged. This was simple to rectify as it simply switches from internal battery to external battery.
Another thing which is odd is the 2 small 100pF capacitors C4 on my layout, (at first I thought they were back to back diodes as I have not seen this style of capacitor before) look like they may have been an addition and only seem to be switched into circuit when S5 is in the middle position.
S4 and S5 are on a single 2 wafer rotary switch, S41 and S42 are on the top wafer and S5 is on its own on the bottom wafer. (sorry I forgot to mark S41 on left & S42 on right separately)
Another thing which leads me to believe that some of the wiring has been altered is the quality of the soldering, some wires look like they have only just been tacked on, and there are 2 rubber insulated stranded wires (all the rest are solid copper with black sleeving on) one is connecting C4 to the terminal, and the other is connecting the wiper of VR1 to the ground terminal on the transformer. (sorry I also forgot to identify bottom terminal of T1 primary is grounded)
So at the moment if I connect a DMM on the phones terminals, and a 100 ohm resistor between the terminals marked R, I do get a null which seems to give an appropriate reading on the scale, (vibrator is also still working at this point)
But I dont know what the other variable resistor VR2 is for, it is marked P.F. Bal, could it be power factor, they have used for µµF for pF on the face plate so I dont think it stands for pF. It is wired in series with the 1µF capacitor C3.
I would be very grateful for any help with confirming the circuit.
thanks
Mike
p.s.
What year do you reckon for this instrument, I entered it into the Radio Museum as 1935 (guess) but I now think about the same age as my early KB radios so late 20's say about 1928. https://www.radiomuseum.org/r/standard_p...r1185.html
Thanks for your replies, the problem is if you look at S3, a DSDP switch (or change over switch) intended I believe to switch from resistance measurement to capacitor measurement, you will see that the 2 central common terminals have been bridged together. There are 2 other wires, one from R3 R2 R1 common and one from the switch itself which are soldered together. I cant work out how these would have been fitted to the switch.
I would have thought that for resistance measurement the vibrator, which incidentally is working, would have been switched out of circuit as DC is all that is required. At the moment S3 seems to not do much, there is a slight change in the vibrator when it is changed over from R to C.
A similar thing had been done with S1 which was faulty, it had been rewired and the 2 common terminals had been also bridged. This was simple to rectify as it simply switches from internal battery to external battery.
Another thing which is odd is the 2 small 100pF capacitors C4 on my layout, (at first I thought they were back to back diodes as I have not seen this style of capacitor before) look like they may have been an addition and only seem to be switched into circuit when S5 is in the middle position.
S4 and S5 are on a single 2 wafer rotary switch, S41 and S42 are on the top wafer and S5 is on its own on the bottom wafer. (sorry I forgot to mark S41 on left & S42 on right separately)
Another thing which leads me to believe that some of the wiring has been altered is the quality of the soldering, some wires look like they have only just been tacked on, and there are 2 rubber insulated stranded wires (all the rest are solid copper with black sleeving on) one is connecting C4 to the terminal, and the other is connecting the wiper of VR1 to the ground terminal on the transformer. (sorry I also forgot to identify bottom terminal of T1 primary is grounded)
So at the moment if I connect a DMM on the phones terminals, and a 100 ohm resistor between the terminals marked R, I do get a null which seems to give an appropriate reading on the scale, (vibrator is also still working at this point)
But I dont know what the other variable resistor VR2 is for, it is marked P.F. Bal, could it be power factor, they have used for µµF for pF on the face plate so I dont think it stands for pF. It is wired in series with the 1µF capacitor C3.
I would be very grateful for any help with confirming the circuit.
thanks
Mike
p.s.
What year do you reckon for this instrument, I entered it into the Radio Museum as 1935 (guess) but I now think about the same age as my early KB radios so late 20's say about 1928. https://www.radiomuseum.org/r/standard_p...r1185.html
