Post by trombone on Mar 31, 2020 13:33:00 GMT 12
Usually when we open a vintage radio up we can see the footsteps of those who have preceded us. Some of the filter caps will be more modern, there are non vintage resistors amongst the old carbon ones. Sometimes we find the penciled initials of a past service man or a date when repairs have been done.
This Philco car radio bore some similar hallmarks of previous work.
It was a great box of a thing , half the size of a biscuit tin,and sadly had lost the bowden cable drives and head unit and some turkey had put a 12 volt vibrator in it, probably because it fitted.There were no model numbers or any indication of its date anywhere , unlike the shortly to be mentioned Model 1540 which has the schematic and part location details on a printed sheet helpfully pasted inside.
Some of the valve dater detectives among you will be able to date this set quite precisely - the line up was 78 , 6A7 , 78 , 75 , 41 and 84. I am still working on a very similar Philco Model 1540 which was made for a 1938 Ford. It has the same valve line up except it has a 42 output tube.Most Philco car radio circuits of this time seem, if Rider is anything to go by, to be very similar.
So what of this headless Philco? What marks were there of previous service?First, the old e.m. speaker had gone, to be replaced by a (Japanese? )p.m. unit of similar size.Someone had fitted a new coupling condenser between the 75 and the 41.But that was it. The buffer cap looked original. The old Philco H.T. filter caps were still there,and worked,more or less.A couple of resistors looked newer but the tell tale gleam of newer solder, the fragment of wire of a different diameter to the rest left on a valve socket pin was not there. Not too much work done, then , in the past.
So lets fit a 6 volt vibrator , apply 6 volts and see what happens.
Nothing. Try whacking the vibrator with a screwdriver handle. A short but unsustained and definitely lower key buzz.And the bench power supply showed only 3 amps drawn even during the short but unsustained buzz.Those of you who do car radios of this vintage will know you work on the bottom (mostly) or the top. They are not easy to turn over especially when you have all sorts of leads going in to give life support.But it was time to turn it over to do that most basic of checks -are the valves glowing?Well - not really.And remember the head unit had gone so no dial light to check for brightness.
Some Eureka moments are there like a flash. Others are more of the slow but building up type.And bear in mind that this was a covid 19 at-last- I- can- fix- all- my- radios- uninterrupted- by- having- to- go- to- work 11:15p.m. moment.
Which one of us is the turkey here?Checking the filament wiring for voltage was inconclusive and confusing.Checking the filament wiring for continuity showed a lead from one 78 socket to another but no other connection whatsoever.The filaments of the 78s at least were wired in series!
And so it all proved to be.Fitted with a 12 volt vibrator which was given the obligatory whack the set burst into boils,buzzy as you'd expect but remarkably loud and very sensitive.
So here's the question.Every one knows American cars were 6 volt right up to about 1955 and some later.Apparently all Philco car radios were 6 volt over this period.But was this set re wired for 12 volts by an incredibly neat and tidy soldering iron genius who could series wire the filaments and leave no trace?Or was it a special run of 12 volt factory wired Philcos for sale to the N.Z. market where English 12 volt cars seemed to be in the majority? Are vibrator transformers robust enough to take either 6 or 12 volts without complaint, because the transformer looks absolutely original externally and does not get warm? Some one will know the answer to the transformer question. On reflection (in the daylight) the fact that the H.T. is about right would suggest a 12 volt transformer. Maybe someone will know if the factory wired option is correct.Or am I going to have to do remedial soldering practice to lift my own level to the "factory wired pass merit excellence "standard?
And so back to the bubble. Cheers everyone.
This Philco car radio bore some similar hallmarks of previous work.
It was a great box of a thing , half the size of a biscuit tin,and sadly had lost the bowden cable drives and head unit and some turkey had put a 12 volt vibrator in it, probably because it fitted.There were no model numbers or any indication of its date anywhere , unlike the shortly to be mentioned Model 1540 which has the schematic and part location details on a printed sheet helpfully pasted inside.
Some of the valve dater detectives among you will be able to date this set quite precisely - the line up was 78 , 6A7 , 78 , 75 , 41 and 84. I am still working on a very similar Philco Model 1540 which was made for a 1938 Ford. It has the same valve line up except it has a 42 output tube.Most Philco car radio circuits of this time seem, if Rider is anything to go by, to be very similar.
So what of this headless Philco? What marks were there of previous service?First, the old e.m. speaker had gone, to be replaced by a (Japanese? )p.m. unit of similar size.Someone had fitted a new coupling condenser between the 75 and the 41.But that was it. The buffer cap looked original. The old Philco H.T. filter caps were still there,and worked,more or less.A couple of resistors looked newer but the tell tale gleam of newer solder, the fragment of wire of a different diameter to the rest left on a valve socket pin was not there. Not too much work done, then , in the past.
So lets fit a 6 volt vibrator , apply 6 volts and see what happens.
Nothing. Try whacking the vibrator with a screwdriver handle. A short but unsustained and definitely lower key buzz.And the bench power supply showed only 3 amps drawn even during the short but unsustained buzz.Those of you who do car radios of this vintage will know you work on the bottom (mostly) or the top. They are not easy to turn over especially when you have all sorts of leads going in to give life support.But it was time to turn it over to do that most basic of checks -are the valves glowing?Well - not really.And remember the head unit had gone so no dial light to check for brightness.
Some Eureka moments are there like a flash. Others are more of the slow but building up type.And bear in mind that this was a covid 19 at-last- I- can- fix- all- my- radios- uninterrupted- by- having- to- go- to- work 11:15p.m. moment.
Which one of us is the turkey here?Checking the filament wiring for voltage was inconclusive and confusing.Checking the filament wiring for continuity showed a lead from one 78 socket to another but no other connection whatsoever.The filaments of the 78s at least were wired in series!
And so it all proved to be.Fitted with a 12 volt vibrator which was given the obligatory whack the set burst into boils,buzzy as you'd expect but remarkably loud and very sensitive.
So here's the question.Every one knows American cars were 6 volt right up to about 1955 and some later.Apparently all Philco car radios were 6 volt over this period.But was this set re wired for 12 volts by an incredibly neat and tidy soldering iron genius who could series wire the filaments and leave no trace?Or was it a special run of 12 volt factory wired Philcos for sale to the N.Z. market where English 12 volt cars seemed to be in the majority? Are vibrator transformers robust enough to take either 6 or 12 volts without complaint, because the transformer looks absolutely original externally and does not get warm? Some one will know the answer to the transformer question. On reflection (in the daylight) the fact that the H.T. is about right would suggest a 12 volt transformer. Maybe someone will know if the factory wired option is correct.Or am I going to have to do remedial soldering practice to lift my own level to the "factory wired pass merit excellence "standard?
And so back to the bubble. Cheers everyone.
