01-07-2006, 10:48 PM
Hi Fred,
Not a Philco, but I do have a 1946 Zenith 8G005 TransOceanic which is 100% original and still playing strong.
I have had a few 1930's radios which seemed to play OK at initial testing, but I never had nerve enough to play them regularly without at least a partial recapping.
The problem with playing original radios like these is the possibility of damage to major components if caps should fail. Not so much of an issue with my T-O, since it is an AC/DC radio with no power transformer at risk, and neither the rectifier or output tubes are particularly rare or expensive. But this is not the case with a nice AC radio like your 37-670.
The problem with electrolytic filter caps is that they can fail two ways, they can either become leaky, or they can short. When they leak this shows up as increased hum, telling you something is wrong and giving you the chance to replace the filters. Usually no harm is done if dealt with promptly. Shorting is more rare, but certainly does happen. Unfortunately when it occurs it is usually without any warning, and depending on whether it is the input or output filter cap which shorts the speaker field coil, rectifier tube, and/or power transformer are at risk. At a bare minimum, if I were operating a 1930's radio with original filter caps I would install a line fuse ahead of the power transformer. In the event of a short this would hopefully protect the transformer, but not necessarily the rectifier tube or field coil.
Another issue is the coupling caps to the power output tube grids. If leaky (and yours most certainly are, to some extent) this is upsetting bias on the output tubes, might not be too noticeable for a while, but if it gets worse the output tubes and output transformer are at risk.
Each person has to make his own decision on whether to leave an original radio "as-is" or not. If played only very rarely, maybe it is worth leaving it original and taking the risk. But if played more often, my best advice is AT A MINIMUM to replace the electrolytic filter caps and the coupling caps to power output tube grids.
If a person decides to leave the radio original and plans to play it on even the rarest of occasions, he should at least use an AC ammeter and see how much current it is drawing. If substantially over nameplate rating this is a sign that its power supply is being stressed and it should not be played again until serviced.
Poston
Not a Philco, but I do have a 1946 Zenith 8G005 TransOceanic which is 100% original and still playing strong.
I have had a few 1930's radios which seemed to play OK at initial testing, but I never had nerve enough to play them regularly without at least a partial recapping.
The problem with playing original radios like these is the possibility of damage to major components if caps should fail. Not so much of an issue with my T-O, since it is an AC/DC radio with no power transformer at risk, and neither the rectifier or output tubes are particularly rare or expensive. But this is not the case with a nice AC radio like your 37-670.
The problem with electrolytic filter caps is that they can fail two ways, they can either become leaky, or they can short. When they leak this shows up as increased hum, telling you something is wrong and giving you the chance to replace the filters. Usually no harm is done if dealt with promptly. Shorting is more rare, but certainly does happen. Unfortunately when it occurs it is usually without any warning, and depending on whether it is the input or output filter cap which shorts the speaker field coil, rectifier tube, and/or power transformer are at risk. At a bare minimum, if I were operating a 1930's radio with original filter caps I would install a line fuse ahead of the power transformer. In the event of a short this would hopefully protect the transformer, but not necessarily the rectifier tube or field coil.
Another issue is the coupling caps to the power output tube grids. If leaky (and yours most certainly are, to some extent) this is upsetting bias on the output tubes, might not be too noticeable for a while, but if it gets worse the output tubes and output transformer are at risk.
Each person has to make his own decision on whether to leave an original radio "as-is" or not. If played only very rarely, maybe it is worth leaving it original and taking the risk. But if played more often, my best advice is AT A MINIMUM to replace the electrolytic filter caps and the coupling caps to power output tube grids.
If a person decides to leave the radio original and plans to play it on even the rarest of occasions, he should at least use an AC ammeter and see how much current it is drawing. If substantially over nameplate rating this is a sign that its power supply is being stressed and it should not be played again until serviced.
Poston
