12-30-2019, 03:35 PM
Greetings everyone,
Working on a Philco 41-610P code 121. It's my desire to spend as little as possible (time or money) to figure out if it's worth saving. To start i did some basic repair to the unit,replaced the filter caps,repaired broken/chewed up wiring. Even managed to rewind a coil on the oscillator. I also replaced one cap that the mice completely chewed through. At this point i decided to power it up on a variac using the dim bulb method. At about 50v the indicator bulbs began to glow, drawing about 20 watts at this point. Slowly increased voltage. At about 80v ,30 watts I started to hear faint noise as I let the radio warm up. I was able to tune in a local station.It sounded weak of course but the audio was distorted too. I checked plate and grid voltages which were kinda high, tube 41 plate was at 190v, schematic called for 165v, for example. Checking the other tubes revealed higher voltages as well. I then decide to re-cap the radio as most of the original caps were still in place and checked the resistors i could while i had the tubes out. I then slowly powered the radio back up. At about the same voltage on the variac i began to hear noise,tuned in the local station. Audio sounded much better. I then went up to 90v on the variac, drawing about 43 watts and the radio really came back to life. Audio was crisp and clear and was able to tune in more stations.Short wave and the phono amplifer also worked. I then checked plate and grid voltages and to my disappointment all were reading even higher relative to their rated voltages on the schematic. The 41 plate was now reading about 210 volts,should be 165.Voltage just after the rectifier but before the field coil was reading 250v,should be 225v. I can only guess what the voltages would be if i went any higher on the variac (roman candles came to mind).
I was expecting lower voltages with the radios age. To me it seems like the radio isn't drawing enough power. My question is this, As tubes age do they tend to draw less power,causing voltages to rise? I don't have a tube checker yet,haven't really needed one up until now i guess. I'm having trouble zeroing in on any one cause of the higher voltages. In the forums experience,am I looking at a total rebuild? My experience is limited with antique radios,it is a hobby. I've repaired a half dozen or so pre 1960's radios with success. I'm kind of at a loss on this one. I attached the schematic i'm using.
Thanks in advance for any help or pointers.
Working on a Philco 41-610P code 121. It's my desire to spend as little as possible (time or money) to figure out if it's worth saving. To start i did some basic repair to the unit,replaced the filter caps,repaired broken/chewed up wiring. Even managed to rewind a coil on the oscillator. I also replaced one cap that the mice completely chewed through. At this point i decided to power it up on a variac using the dim bulb method. At about 50v the indicator bulbs began to glow, drawing about 20 watts at this point. Slowly increased voltage. At about 80v ,30 watts I started to hear faint noise as I let the radio warm up. I was able to tune in a local station.It sounded weak of course but the audio was distorted too. I checked plate and grid voltages which were kinda high, tube 41 plate was at 190v, schematic called for 165v, for example. Checking the other tubes revealed higher voltages as well. I then decide to re-cap the radio as most of the original caps were still in place and checked the resistors i could while i had the tubes out. I then slowly powered the radio back up. At about the same voltage on the variac i began to hear noise,tuned in the local station. Audio sounded much better. I then went up to 90v on the variac, drawing about 43 watts and the radio really came back to life. Audio was crisp and clear and was able to tune in more stations.Short wave and the phono amplifer also worked. I then checked plate and grid voltages and to my disappointment all were reading even higher relative to their rated voltages on the schematic. The 41 plate was now reading about 210 volts,should be 165.Voltage just after the rectifier but before the field coil was reading 250v,should be 225v. I can only guess what the voltages would be if i went any higher on the variac (roman candles came to mind).
I was expecting lower voltages with the radios age. To me it seems like the radio isn't drawing enough power. My question is this, As tubes age do they tend to draw less power,causing voltages to rise? I don't have a tube checker yet,haven't really needed one up until now i guess. I'm having trouble zeroing in on any one cause of the higher voltages. In the forums experience,am I looking at a total rebuild? My experience is limited with antique radios,it is a hobby. I've repaired a half dozen or so pre 1960's radios with success. I'm kind of at a loss on this one. I attached the schematic i'm using.
Thanks in advance for any help or pointers.
