Need some help with an old PHILCO radio.

[RayRay1132]

Already explained in post #13 by danadak.

Not good for squeezing in a car

Where I used to work the previous chief engineer used to be a policeman in Manchester long ago, and one of the things he was involved in was early experiments with radio transceivers in the police cars - pretty large back then. Two souveniers he had from his police days were a set of brass knuckles, and a huge great knife - standard Police equipment back in those days in Manchester



You'd like to think so?, I gave up trying to find a schematic as all the ones I tried wanted to charge you for them, but the postage stamp sized pictures seemed to show a mains transformer, and as you'd expect it looked a fairly bog standard valve radio.

It does have a power transformer

 

[RayRay1132]

so, it must be using a power transformer...

yes

 

[Reloadron]

. You should be able to use Schematics 1 & 2 to trace your signal start to stop. It's pretty straight forward. Hopefully you have a scope or something to use as a signal tracer.

Ron

 

[Nigel Goodwin]

. You should be able to use Schematics 1 & 2 to trace your signal start to stop. It's pretty straight forward. Hopefully you have a scope or something to use as a signal tracer.

Valve radio and a scope?

Analogue meter and a wet finger - that's generally all you ever need.

I made a suggestion earlier to test the audio stages, but he's never come back and mentioned if he's done that or not - if he had I'd have offered further advice.

For radio repairs generally, signal injection rather than tracing is more useful, and a lot cheaper and simpler - all you need to do is throw a multi-vibrator together - about 1KHz or so will do for audio, IF and RF. However, I don't recall ever needing it on valve radios? - they are generally so simple to repair.

 

[rjenkinsgb]

.

There is a free one in the service book I linked to earlier, rather than paying!

 

[Nigel Goodwin]

There is a free one in the service book I linked to earlier, rather than paying!

Nice layout drawing of the chassis as well - interesting (as already mentioned) that it appears to be a car radio sort of shape, with the controls arranged accordingly, and even inductive tuning (common in car radios, rare in home radios) - but then a bleeding great big transformer sat on top of the chassis

 

[Reloadron]

There is a free one in the service book I linked to earlier, rather than paying!

Paying? I clicked each image, expanded each image and just saved them and then pasted them. You can use any image software like even paint or the Apple equivalent. Problem is the images are a little large to post. They are easy enough to follow.

Ron

 

[Reloadron]

Valve radio and a scope?

Analogue meter and a wet finger - that's generally all you ever need.

I made a suggestion earlier to test the audio stages, but he's never come back and mentioned if he's done that or not - if he had I'd have offered further advice.

For radio repairs generally, signal injection rather than tracing is more useful, and a lot cheaper and simpler - all you need to do is throw a multi-vibrator together - about 1KHz or so will do for audio, IF and RF. However, I don't recall ever needing it on valve radios? - they are generally so simple to repair.

Yes, I agree and that served me well enough for years. I just had reservations about suggesting a wet finger to see if B+ was present. A big step for me was a hand me down VTVM and a later built Knight Kit signal tracer. They are not very challenging to find a problem on but even with a schematic if someone is not familiar with schematics and symbols I guess they can be a challenge. Beats me but now if they come back they can have a cartoon to work from.

Ron

 

[unclejed613]

by the way, a lot of manufacturers back then used paper capacitors for screen and plate circuit bypass caps, as well as interstage coupling caps. paper caps that old have a very high failure rate, if it were me i would outright replace them with mylar caps. my first experience with this was an E.H. Scott radio my grandfather gave me... i found a shorted paper plate circuit cap in it, replaced it with a mylar, and it worked.... for a couple of days. so this time it was another paper bypass cap somewhere else, replaced it, the radio worked for a week. after finding a third bypass cap shorted, i counted all the paper caps that had 100V or more across them, and ordered a bunch of mylars to replace them. the only cap that failed after that was a mica cap that was in a hard to find place.
if your radio has paper caps, especially in use as bypass caps, i recommend replacing them, and make sure you always connect the outside foil end of the cap to ground, especially in the RF, LO, and IF stages.

one clue of a shorted paper cap is the wax has melted out of it, or the cap could be discolored from heat.

 

[Nigel Goodwin]

Back in the 'olden days' a common (and VERY effective) technique was to replace any Wima capacitors - they WOULD be faulty. If that didn't solve the problem, you could then start fault finding further - but there was little point doing so while Wima caps were still in place.

 

[rjenkinsgb]

Another thing worth trying before further work is just to clean the pins on the valves.

They can corrode / tarnish badly over time and lose contact with the socket. If they look black, a clean with some very fine wet & dry or emery cloth may kick things in to life?