06-21-2024, 12:14 AM
Hi all,
I am new to this forum. I am at a loss trying to refurbish a friends Philco 46-1203 radio/phonogragh. A little bit about me - I am a retired mechanical and manufacturing engineer with a hobby of refurbishing older audio equipment. Mostly amps, receivers, tape decks, etc. I'm not an electronics expert but have been educating myself in diagnosing and repairing audio stuff.
My experience with tube gear is limited. I successfully refurbished a McIntosh tube amp and preamp for a neighbor so this Philco is not my first. The unit belongs to a friend and is a family heirloom for her. She just wants to get it working again. The unit was intact and in decent physical shape.
Upon receipt I brought the unit up slowly on a variac and dim bulb tester. No drama, the dial light came on but the turntable didn't spin. The needle is intact but no sound from tapping on it. The radio also has no sound - not even static. The turntable motor was gummed up and frozen. I was able to get it freed up and the turntable now functions - but no sound.
I started by replacing the caps. They were basically all bad and I replaced all except a few square shaped caps with round dots. They tested good and are not likely failure points from what I understand. After replacing the caps - still no sound. Next I took the tubes to a local electronics store (blast from the past) that still has a tube tester. They tested on the weak side but useable. Since I get no sound from either the radio or the phono - I focused on the audio output and rectifier tubes. I got replacements for those just in case. Still no sound. FYI - this unit came with a 50Y6 rectifier tube not the 50X6 listed on the schematic. The 50Y6 is the correct tube per the diagram on the inside of the cabinet.
I'll try and shorten the story and give a bullet list of what I've done so far.
1) replaced all electrolytic and wax caps.
2) Replaced all tubes
3) checked the speaker for function - ok
4) checked all carbon resistors - all checked good.
5) checked the main switch and volume control resistance values - ok
6) checked the output transformer - removed it checked primary secondary coil resistance - ok (it also passed a signal from signal generator).
7) removed the IF transformers and checked coils - ok
I'm not sure what to do next. The only sound is a vary faint hum. You have to put you ear to the speaker to hear it. It doesn't appear anything is shorted - no dim bulb light. I seems something is open in the amplifier section but I cannot find what. There really isn't that much to this thing. I downloaded the Philco service training manual from the library and tried applying a signal to various places to find where it's dying. I was able to get sound out from all 3 test positions but only when the negative lead from the signal generator went to B-. Sound came out but it lit up the dim bulb ( it also cooked my signal generator).
Anyway, if anyone has some gentle advice on what to do next it would be greatly appreciated.
I am new to this forum. I am at a loss trying to refurbish a friends Philco 46-1203 radio/phonogragh. A little bit about me - I am a retired mechanical and manufacturing engineer with a hobby of refurbishing older audio equipment. Mostly amps, receivers, tape decks, etc. I'm not an electronics expert but have been educating myself in diagnosing and repairing audio stuff.
My experience with tube gear is limited. I successfully refurbished a McIntosh tube amp and preamp for a neighbor so this Philco is not my first. The unit belongs to a friend and is a family heirloom for her. She just wants to get it working again. The unit was intact and in decent physical shape.
Upon receipt I brought the unit up slowly on a variac and dim bulb tester. No drama, the dial light came on but the turntable didn't spin. The needle is intact but no sound from tapping on it. The radio also has no sound - not even static. The turntable motor was gummed up and frozen. I was able to get it freed up and the turntable now functions - but no sound.
I started by replacing the caps. They were basically all bad and I replaced all except a few square shaped caps with round dots. They tested good and are not likely failure points from what I understand. After replacing the caps - still no sound. Next I took the tubes to a local electronics store (blast from the past) that still has a tube tester. They tested on the weak side but useable. Since I get no sound from either the radio or the phono - I focused on the audio output and rectifier tubes. I got replacements for those just in case. Still no sound. FYI - this unit came with a 50Y6 rectifier tube not the 50X6 listed on the schematic. The 50Y6 is the correct tube per the diagram on the inside of the cabinet.
I'll try and shorten the story and give a bullet list of what I've done so far.
1) replaced all electrolytic and wax caps.
2) Replaced all tubes
3) checked the speaker for function - ok
4) checked all carbon resistors - all checked good.
5) checked the main switch and volume control resistance values - ok
6) checked the output transformer - removed it checked primary secondary coil resistance - ok (it also passed a signal from signal generator).
7) removed the IF transformers and checked coils - ok
I'm not sure what to do next. The only sound is a vary faint hum. You have to put you ear to the speaker to hear it. It doesn't appear anything is shorted - no dim bulb light. I seems something is open in the amplifier section but I cannot find what. There really isn't that much to this thing. I downloaded the Philco service training manual from the library and tried applying a signal to various places to find where it's dying. I was able to get sound out from all 3 test positions but only when the negative lead from the signal generator went to B-. Sound came out but it lit up the dim bulb ( it also cooked my signal generator).
Anyway, if anyone has some gentle advice on what to do next it would be greatly appreciated.
