Hey folks, I have an old Philips valve radio where when its turned on, the sound changes where it distorts and the sound goes weird and often cuts out. To get the radio sounding back normal again, I turn it off and on or fiddle with the volume knob and it clicks back to normal. I do this about 3 to 4 times until the radio heats up and when it does heat up there's no more glitching or intermittent problems. In fact it can sit for hours and be fault free.

Any ideas?

Thanks guys.

Steven

It could be a lazy switch contact. However, how old is it and when was it overhauled if ever.

Normally with a tube radio there is a normal lag of several seconds until the heaters in the tubes get mobile an cause the tubes to conduct.

Where there a filament rectifiers these get mobile very quickly causing a high voltage surge, which is bled off when the slower heater tubes get going. It is not unusual for that over voltage to cause distortion as the voltage comes down to normal.

Some converter tubes will also drift upwards in frequency until they reach operating temperature.

So, in all but a few sets, if its got valves there will be a delay, before the valves / tubes get going: They are not instant. However this one could have an impending internal power supply issue due to old parts.

Has it had its capacitors replaced?

Yes it has been recapped recently

Playing with the mains is to be avoided but sometimes its unavoidable. So what I would do for one is use an ohm meter on the plug top (the cable is implicated) and see if you get continuity when you switch it to on. (Not plugged in). There were a couple of careless electricians at one place I worked, who proved that you cannot measure the resistance of a 415V supply: Blue flashes and smoke....

Another is to leave that switch in the "on" (radio running) position and turn it off at the power point. Then come back to it in the morning an see if it fires up. If it does that with out fail; Then the switch is possibly faulty.

If it fails to fire up move the cable at places like the plug top & where it enters the radio. If there has been a lot of flexing, or twisting from bad securing, there can be internal wire breaks within the cable. Loose screws & dry joints also do that.

Feedback results.

Radio model could be useful.

Also be aware that some Philips transformers are prone to having winding wire exit the sides. Don't put your fingers on it, that will cause corrosion.

Ah yeah I had forgotten. Almost every radio in my collection when received had loose screws in the power plug. This needs to be checked and rectified.

As a generalisation with mains operated radios; The mains side of radios does not get a lot of attention and many that have wandered in vary from good, to not real good, to tatty, then the various levels of dangerous to lethal.

Like a couple that have come in where diddums has naturally, in blissful ignorance and exuberance plugged it in to see if it works and the mains lead is stuffed rubber and a series of 3/16" beads,

Step one here, irrespective of battery, or mains; is to assess it to see if it is safe for you, or it to power. Powering can do quite a lot of damage, when applied inappropriately and one may not be able to economically fix it, after that episode.

I have noted before that items like cables donated to the local Mens shed, often in "good faith" from deceased estates where dad had turned up his toes. OR Dumping: Some of that can be good.

However, on Tag & Test it was not unusual to get over 10% that mechanically & electrically just did not measure up an some were seriously dangerous. I recommended that one person supervised incomings and irrespective of what it was, it did not go for sale, or use internally, without inspection & clearance.