An Introduction and a Philco 90 issue. - Printable Version
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RE: An Introduction and a Philco 90 issue. - cknob - 11-24-2021
When I do what you just said, I get 1.75 kilo ohms 1750 ohms
RE: An Introduction and a Philco 90 issue. - cknob - 11-24-2021
195 ohms from the first terminal to the chassis and from end to end of the resistor I get 1750 ohms
RE: An Introduction and a Philco 90 issue. - Steve Davis - 11-24-2021
Something is not right. The three sections of the BC resistor should add up to about 3740 ohms, may read slightly less because of the circuits connected to it, 1750 sounds low.
Steve
RE: An Introduction and a Philco 90 issue. - cknob - 11-25-2021
Happy Thanksgiving to all.
RE: An Introduction and a Philco 90 issue. - Steve Davis - 11-26-2021
Chris, disconnect the wires from terminals 3 and 4 and recheck the resistance of all sections of the B-C resistor.
Steve
RE: An Introduction and a Philco 90 issue. - cknob - 11-26-2021
Hi Steve...hope you and your family had a wonderful Thanksgiving. Thanks for not giving up on me here!! I'm feel pretty discouraged and I'm afraid I'm getting close to walking away
I think the resistor is fine...I took it completely out of circuit as you see below and measured it. 4k ohms from end to end. From 1 to 2 193 ohms. 1 to 3 254 ohms. The internal measurements make sense too. From 2 to 3 60 ohms. From 2 to 4 3.8k ohms.
Any suggestions as to what I should test or do next? Thank you for your help...it's much appreciated!
RE: An Introduction and a Philco 90 issue. - Steve Davis - 11-27-2021
With the resistor disconnected measure the resistance from chassis to each wire removed from terminals 3 and 4.
Steve
RE: An Introduction and a Philco 90 issue. - cknob - 11-27-2021
Chassis ground on the meter and test lead to wire that was connected to terminal 3 shows 0 ohms. I then connected the test lead to the line that was attached to terminal 4 and got 3200 ohms. That wire from terminal 4 terminates and is soldered to one of the external speaker sockets.
RE: An Introduction and a Philco 90 issue. - Steve Davis - 11-27-2021
The wire from terminal 3 should read infinity, it sounds like it may be miswired. Trace it out, comparing it to the schematic. I think you are very close to finding the problem.
Steve
RE: An Introduction and a Philco 90 issue. - Steve Davis - 11-27-2021
After looking at the schematic again, it looks like we have a problem with the connection to terminal 4 also. That one should read about 50K. While reading the terminal 4 wire, unplug the speaker and see if the reading goes up. if so, one or both of the filter cap is shorted.
Steve
RE: An Introduction and a Philco 90 issue. - cknob - 11-27-2021
The resistance on the speaker socket goes up to 90k ohms when the speaker is unplugged. Do you mean the AC filter caps or the electrolytics?
RE: An Introduction and a Philco 90 issue. - Steve Davis - 11-27-2021
Yes, the filter caps items 56 and 57. I believe one or both are shorted. I should mention, these are DC not AC. Remove them, plug the speaker back in and recheck the resistance on terminal 4 wire again, I think the reading will go up to the 90K that you had with the speaker unplugged.
Steve
RE: An Introduction and a Philco 90 issue. - cknob - 11-27-2021
I cut the electrolytics out of circuit (I should mention the BC resistor is still disconnected and out of the radio so the filter cap that's connected to BC resistor terminal 1 was already out of circuit) and I'm getting the same resistance measurements...3200 ohms when the speaker is plugged in and 90k ohms when the speaker is unplugged. I'm measuring this with my meter black lead clamped to the chassis and I'm measuring the terminal on the speaker socket that is normally connected to terminal 4 of the BC resistor with the meter red test lead. Just trying to be exhaustively clear so you can tell if I'm doing something dumb! Thanks so much for this help!
RE: An Introduction and a Philco 90 issue. - Steve Davis - 11-27-2021
I'm not sure what is going on here. With the speaker unplugged we are reading the resistance of resistors 49 and 50. with the speaker plugged in we seem to be reading the speaker field coil but I don't understand how. The number 4 wire connects to the upper end of the coil but the lower end of the coil should nowhere be connected to chassis ground, that is why I suspected a shorted filter cap. Maybe someone will jump in and help us here. CALLING TERRY! ....... ANYONE!
For now let's move to the terminal 3 wire. We have zero ohms here, should be infinity. Looking at the schematic, you can see this wire connects only to the cathodes of several tubes and should not have any connection to chassis ground. Trace this circuit looking for an error.
Steve
RE: An Introduction and a Philco 90 issue. - cknob - 11-27-2021
Thank you Steve. According to the schematic, the wire from 3 goes to the oscillator and to the detector amp tube 27 correct? I will trace that out. Would more detailed pictures of the trace of wires from 3 and 4 help?