Philco 66 - Sweet Music at Last!! - Printable Version
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+--- Thread: Philco 66 - Sweet Music at Last!! (/showthread.php?tid=4640)
RE: Philco 66 - Coil troubles? - jerryhawthorne - 05-25-2012
Has the OP given up? Like to see this continue to completion.
Jerry
RE: Philco 66 - Coil troubles? - jph14 - 05-26-2012
Waiting for supplies. Will be resuming work shortly. Currently working on cabinet and checking over everything I've done on chassis. Jerry- still no loud hum on center post of vol. control.
Thanks for asking.
Joe
RE: Philco 66 - Coil troubles? - jerryhawthorne - 05-26-2012
Joe, really need to get the audio amp section working well before chasing signals from the antenna or injection of signals from your generator. Particularly if your working without a scope. If your using the speaker output to do things and the amp is not working properly, well, it's like working in the dark. Tone insertion on the control grid of the output tube and the first audio seem to be the next phase as was indicated earlier. You will be after the volume control so keep the generator audio gain down low. Hate to see you put a large signal in and launch your speaker cone. Needless to say, you also need to confirm the voltages on the two tubes. Something is wrong in the audio if your not getting a hum out while touching the center tap of the volume control with the volume up. Voltage measurements will give you good idea where the problem is. Signal input to the two control grids will also tell you which section. It could be something as simple as the wires going to the speaker are not wired correctly. They are color coded on the schematic. I only suggest that as you indicated in a previous post that they were disconnected.
Good luck and we are watching. The audio section is pretty straight forward.
Jerry
RE: Philco 66 - Coil troubles? - jph14 - 05-27-2012
Jerry,
Took your advice - checked voltages on 42 and 75 tube.
42-- P-K= 281 vdc
Sc-K= 269 vdc
g-k= -16.5vdc
75-- P-K= 8.5 vdc-- sould be around 160. Backtracked to resistor 28 and 29- should be 70,000 ohms each- 75,000 are in there now. Will this cause such a voltage drop?
RE: Philco 66 - Coil troubles? - codefox1 - 05-27-2012
resistor 28 and 29 can be 75k or 70 K but may have drifted way say up oropend. Parts 27,30,31 could also be involved. Check voltage divider to confirm that there is B+ going to this stage. You did replace all the caps,right?
Agreed you have to get this stage working before anything else.
RE: Philco 66 - Coil troubles? - jph14 - 05-27-2012
All caps and resistors replaced. Will check 27,30, and 31.
Thanks
Joe
RE: Philco 66 - Coil troubles? - jerryhawthorne - 05-27-2012
Not the sharpest knife in the drawer on this stuff but agree with Joe that info says that the plate of the 75 should be 160 Volts. The way the schematic reads, unless I'm missing an interconnection dot between the line going from the + on the second electrolytic to the 70K resistors, it appears to me there should be a small negative voltage to ground on the plate, derived from the #44 divider? Seems like the line between the + on the second electrolytic needs to pick up some B+ from somewhere. How about the screen of the output tube? The lines cross, but I see no connection dot.
Call me curious but I don't see how to develop 160V on that plate according to how I read that schematic.
Jerry
RE: Philco 66 - Coil troubles? - morzh - 05-27-2012
I think there is a mistake in that sch. There is o DC bias on the 75's pate if you trust it. Can't be that way. Methinks there should be a tedot between #28 70k resistor lower point and the post-fied coil voltage (B+is it), then it makes sense as it also goes to the seond #50 8uF cap.
RE: Philco 66 - Coil troubles? - jerryhawthorne - 05-27-2012
Thanks Mortzh, for vindicating my stupidity. Yes Joe, in case you did some wiring changes please check resistance from the white wire on the speaker plug female connector, you can unplug the speaker if you wish, to the plate of your 75. Should be about 140K. (2X70K) I suspect it will read infinity. Need some B+ up there. You have to get that white wire (trace where it goes to the 44 screen hooked up to the bottom the 70K resistor string or the + of the second 8mfd cap. Hope it will work! Would be my first help in getting something up and running on a Phorum. I think like Mortzh, they missed the dot. Hopefully you will have a working amp at this point and able to check other things. Just give a measurement on plate voltage and see if it does't pop up. If you have some little jumper wires, just hook one up between the two points to see what happens.
Jerry
RE: Philco 66 - Coil troubles? - morzh - 05-27-2012
If I do rewiring, i usually make notes, sice I don't fully trust manuals.
RE: Philco 66 - Coil troubles? - jph14 - 05-27-2012
Thanks! Will give it a try and get back to you guys.
Thanks,
Joe
RE: Philco 66 - Coil troubles? - jph14 - 05-27-2012
Jumpered from the white of the speaker back to terminal board with 28 and 29.
Plate of 75 now at 178 and I have a hum on center tap of vol. control.
Will solder up tom. Where to next?
Thanks,
Joe
RE: Philco 66 - Coil troubles? - jerryhawthorne - 05-27-2012
Great Joe! I probably feel better than you. Next up, start injecting a modulated signal at your IF frequency into the antenna. See if you get anything. Actually I would start by hooking up your antenna, going to AM and see what happens. Report back, a lot more people a lot smarter than me hanging out here. Especially in the front end area. Who knows, the radio may start working now. By the way, I hope the hum you get is strong and varies with the volume control if you are touching the center tap.
Jerry
RE: Philco 66 - Coil troubles? - Radioroslyn - 05-28-2012
Great job guys!! Joe, if you hang around long enough it will rub off onto you.I've got a 66MB out in the shed but too many projects ahead of it. It needs some cabinet work mostly wooden dial escutcheon, looks like someone belt sanded it.
GL
Terry
RE: Philco 66 - Coil troubles? - jerryhawthorne - 05-29-2012
Thanks Terry, it was fun to help with my limited knowledge. Now, let's hear from Joe and see what comes up next!
Jerry