I attempting to restore a 41-290 (code 121) and have identified a couple of discrepancies between the as built (as-manufactured) unit and the available schematics. Specifically, item #41 (resistor) is specified as 33K ohms whereas the resistor installed is 100K ohms and item #45 (capacitor) is specified to be .01 mf where as the installed item is .003 mf. As far as I can tell from visual inspection the 100K ohm resistor and the .003 mf cap appear to be as factory built. The following illustration details the discrepancies.
Any thoughts from the members/experts will be appreciated.
Note from site admin: Sorry, but the photos which were attached to this post are no longer available.
This is a production change, documented in the 1941 RMS Year Book.
Models 41-280, Run 7; 41-285, Run 7; 41-287, Run 7, and 41-290, Run 5
To improve the Bass compensation action in the volume control circuit beginning with the above production run numbers, resistor (41) 33,000 ohms was changed to 100,000 ohms, Part No. 33-410339. Condenser (45) .01 mfds., 400 volts was also changed to .003 mfds., 1000 volts Part No. 30-4469.
There is no need to use a 1000 volt capacitor for part (45). 600 volts is overkill, but it is easier to standardize on 600/630 volt capacitors throughout when buying new caps.
Use of an .003 uF cap for part (45) will give your radio thundering bass. An .01 is too large here to be effective enough for bass compensation, thus the change.
I've modified a few Philcos that had 33K or smaller resistors and .01 uF caps in this circuit. I changed them to 68K and .0047 uF. Result: great bass response.
YMMV.
Thank you for this information - I'll use the .003mf cap and 100K ohm resistor. New ones of course.
TFB
I suppose that this should apply to the 41-250 and 41-255 as well since they use the same chassis as the 41-280 and 41-285 respectively. Yes?
-David
I just looked; the answer is yes.