Philco 49-607 inop - Printable Version
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RE: Philco 49-607 inop - MrFixr55 - 01-17-2025
Consider, at the very least, replacing the caps involved with the audio stages, especially C200, C201, C202 and C204. In addition, the B+ and Cathode Bypass caps are important. These are C1000D, C303, C401 thru 403, C405 thru 407. Failure of any of these caps could cause bias or oscillation issues.
Did you substitute the speaker or merely place it in parallel with the existing speaker? A speaker with an "off center voice coil will sound "raspy" and will get worse as it gets louder.
I often recommend the installation of an Aux input to increase the usefulness of the radio but also to "divide and conquer" as to whether the issue is with the RF / IF / Detector section or the AF Amp section. However, I do not usually do this on AC-DC AA5s and especially not on Battery / Line Power portables for 2 reasons:
1. The power output on these portable sets is only about 0.2W
2. This is a "Warm Chassis" set that has a rather high leakage from chassis to ground depending on power
cord polarity and status of the on-off switch.
However, temporarily disconnecting the radio signal from the volume control and injecting an audio signal from an external source (MP3 Player on its own batteries would be safest) way to do so.
Attached below is a section of the diagram. Cut at the "X" and inject at the arrows, with the "hot"(tip) of the output on the pot side of the X and the ground (shield) of the MP3 to the junction of the pot, R201 and R202. Use an MP3 with an all plastic case or set the MP3 before powering up the radio.
Hope this helps.
RE: Philco 49-607 inop - Tennangler - 01-17-2025
I disconnected the speaker wires before connecting the good 8ohm speaker.
I may try to do the test with an external devise to check the amp. If it is still bad I will replace those caps in the audio circuit.
I have other things I'm working on now and also looking for an old belt to repair the handle on this radio. It really looks good since I cleaned it up.
Thanks for all your help.
James
RE: Philco 49-607 inop - Tennangler - 01-17-2025
Mrfixr55,
Is the X where I disconnect from the volume control and check marks where the output of the Mp3 goes? Is one the ground wire?
Can I use a cell phone or is there a chance of damaging it? How about a transistor radio? I dont have a MP3.
Thank You
RE: Philco 49-607 inop - Tennangler - 01-19-2025
After looking at the schematic closer I understand where to inject the signal. Is it ok to use something other than an MP3 player?
James
RE: Philco 49-607 inop - morzh - 01-19-2025
One has to be careful when using external signal sources with AC/DC radios.
That is, when using the radio that works off of a battery, it is easier, but when it works off the AC, there are issues of handling the galvanically coupled AC outlet, that could be L or N, to what is being used as the common of your signal.
Again, when your MP3 also works off the battery, it is fine.
So is any source that works of isolated AC/DC power supply. But some Isolated supplies still bring Neutral (that is GND, which is same potential as Neutral) to the Negative of their output, which again could create a problem.
Decoupling through transformer/capacitors helps, especially transformer, as it galvanically de-couples the circuits. Capacitors are a bit more tricky, as they allow current flow and so will allow some undesirable conditions to occur, if not paid attention to.