Fading reception (Ekco BPT351)

[Johnbarn]

The 2 photos show an unnamed MW/LW radio I am working on. It's of British manufacture, ELAC speaker, OC44 series transistors, Hunts capacitors. It is well built, perhaps Pye? It wasn't working at all when I got it but changing all the capacitors and electrolytics has it receiving ok. But when I fire it up it gives plenty of volume but this quickly decays to just about audible on R4 MW, better on local BBC. I have no circuit diagram cos I can't identify it. Has anyone any suggestions or does anyone recognise it?

[Nuvistor]

Check the current consumption when working correctly and when faulty, if is goes high it could be the output transistors with thermal runaway.
Frank

[Biggles]

If the sensitivity stays the same under fault conditions but the volume goes low, then that would point to the audio amplifier stage being faulty. If the sensitivity suffers then that would point to the RF or IF stages being the problem. Is it possible to inject an audio signal across the volume pot when the fault occurs to see whether the audio stage is still working? I would personally head for an audio stage fault, and as said in the previous post, measuring current consumption would help. You may find that the current goes up as the fault occurs which would indicate the output stage being faulty.
Alan.

[Johnbarn]

Thanks Alan and Frank, when tuned to a strong signal and at full volume setting on the pot, the radio draws 40mA. At lower volume setting it's steady at 20mA.
With a weaker signal and at normal volume setting the current drops from about 23mA to the quiescent 20mA as the volume fades. John

[Nuvistor]

I would inject a signal as Alan suggested to rule out the audio stages.

Frank

[Johnbarn]

Thanks guys, I'll get a test like you suggest set up in the next few days and get back to you. Anyone any thoughts on the manufacturer/model?

[simpsons]

I believe that this is an Ekco BPT351 1960's radio, also known as a Ferranti PT1030 for which the schematic can be dowloaded FOC.

A number are also for sale on eBay one of which is "as new."

Good luck

Chris

[60 oldjohn]

I have that set with a slightly different front. If you look Very closely at the inside of the back cover you may be able to see some writing, it is just a case of getting it in the right light. I always thought it was an Ekco, never known the number though. Interesting the scale can be read in either direction there is an aerial socket in the base of the set for use in a car. The circuit is available top right of this page.


John

[Nuvistor]

The quiescent current is quoted as 14ma in the service manual for the BPT351, so in your radio it is high.
The service info is available FOC on some sites but the only one I found was the Radio and TV book version. The makers manual is available from this forum site but is £1.99, there is more info in the makers version.
http://www.service-data.com/product....52/2029/m11452

Frank

[Johnbarn]

Thanks to everyone for that information. The circuit details will help get the set working properly. No sign of writing on the inside of the back cover John, just the hardboard cris-cross markings. And yes, there is an aerial socket on the bottom for a car aerial. I must check the eBay advert out of interest. Thank you all. I'll let you know progress.

[paulsherwin]

Check the quiescent current as the volume drops. If it is rising, then one or both of the output transistors is bad. You may be able to feel them getting warm.

[Edward Huggins]

I don't think it's a Pye, especially as early Pye Transistor sets from this period did not use Elac speakers. They mostly used R&A speakers as it was a Pye Group company.

[AC/HL]

It was released in 1959, the year before the Pye took over Ekco/Ferranti to form British Electronic Industries Ltd. (https://en.wikipedia.org/wiki/EKCO)

[Johnbarn]

SUCCESS!!!
Sometimes it's just luck that restores a radio to near perfect working condition. After several weeks wrestling with my fading EKCO/Ferranti PT1030 with the guidance of several correspondents, and having replaced all the Hunts capacitors and all the resistors around the output stage to no avail, I gave up and parcelled the thing up into its case again with a new PP3 battery, (up to then all my testing had been done using a stabilised power supply). I was prepared to accept it as it was with slight fade-down soon after switch on. Today when I switched it on I noticed something that hadn't been apparent before - there was a delay of a second or two before it started. Hmmm, what if there was an intermittent high resistance in the switch contacts? Could that be the problem all along? I replaced the pot and dp switch with a new one and hey presto - a complete cure and the radio sounds great. I'm sure the replacing of all those other components will have improved the quality but the aged switch and pot was the main culprit. Sometimes it's the mechanical bits that can lead us a merry dance. Anyway thanks to all who helped along the way. And I hope this helps someone in the future, John

[paulsherwin]

Good news. Sometimes you do just stumble on a fix like this.