Grundig 80U

[Mike Watterson]

Interference levels, in the main, were quite low in those days so the public saw no reason to splash out considerable sums of money to listen to the same programmes they already had. Therefore, sales levels were low which meant that prices remained high - obviously a far cry from events in Germany!

Except in some parts of the South East even in daytime. Lithuanian Radio was a problem and UK insisted it was a "Pirate" station. It was a Soviet backed station, so not a Pirate in 1960s sense. That sort of interference was why the BBC was asked to look at VHF and eventually allowed to transmit on VHF. It was for a privileged few in the Home Counties. It's in Hansard! Complete VHF roll out took over 20 years!

It's a shame they didn't restart BBC regional radio in 1945 and add commercial Radio in 1955 as well as TV. UK companies were spending with the perfectly legal Luxembourg.

[Terry]

I think you are getting a little confused there, Mike. The transmitter was at Skutari in Albania and supplied to the Albanian government for propaganda broadcasting by the Chinese People's Republic.

See here: https://www.radios-tv.co.uk/an-awkward-customer/

It broadcast as Radio Tirana.

However, this problem didn't start until the mid 60s, by which time FM radios had become a bit more popular but, unfortunately, the country had also been flooded with far eastern radios originally designed for the US market. As the US doesn't have a Long Wave, neither did these sets. Thus the alternative of listening to the 1500m Droitwich transmitter no longer existed for many people.

I'm not aware of any previous forms of co-channel interference affecting either the Light or Home services - and I lived in the South East!

[Amie]

Back with the 80U.

There's no noise from the set on FM, also signal injection to the grid of the valve does nothing.... Removed the valve and injected across the IF transformer, still nothing.

Fault with a secondary on the 10.7 IFT???


Amie

[Terry]

Fault with a secondary on the 10.7 IFT???

Easy enough to check for continuity - note there are three connections to the secondary.

Also, check the two diodes - as they are effectively in series, you can check both at the same time - very low resistance in one direction , high (50k, actually, because of the resistor across them).

Next I'd check the 2µF electrolytic if you get a low reading in both directions.

[pwdrive]

At least half of the secondary winding and the tertiary winding must be ok otherwise AM wouldn't work properly.

Out of interest what modulating frequency are you using and what's the deviation.

Lawrence.

[Mike Watterson]

Electrolytic + terminal usually to chassis / 0V on FM detector and seems to be the electrolytic I've most commonly replaced on mains Valve AM/FM sets.

[Amie]

So, using the scope on the anode of the EBF50 and with the set switched to FM, there was plenty of activity. Tuning through the band, the set was obviously receiving something.

I sat and I stared at the set and the diagram for an hour until I'd convinced myself I'd no clue what was wrong.
I found up a 2.2uF capacitor to replace the one in the detector circuit as suggested and was studying the set as to where to test the last IF secondary again, then it dawned on me there's some little spikes sticking out of where the diodes should be!

Someone had pinched the diodes!

My bum was sore because the radio had been got at by electrocannibals!

I searched out a pair of Russian germanium diodes from a stash that dads (and my) friend Greg had sent him a couple of years ago. They worked a charm (thanks Greg    )

All that's needed now is a tidy up. I won't be trying to excise the old component leads, I will just make some solder buckets to splice the new components neatly. Only a dial lamp is outstanding.

The set will be powered through a "buck" transformer in a box, I found a little (6W) 18volt one for the job.

It only needs a cheapo wall hung wire dipole and it's getting six noise free channels on the FM band, and is booming out Caroline on MW as I type, the HF end of the band is weak though. I'll stop there, I won't want to mess it up in the name of perfection. It does sound rather good for such a small Bakelite radio....

Thanks everyone for their help and Interesting diversions,


Amie

[Amie]

At least half of the secondary winding and the tertiary winding must be ok otherwise AM wouldn't work properly.

Out of interest what modulating frequency are you using and what's the deviation.

Lawrence.

Hey Lawrence.

Sorry I didn't see this post!

400Hz modulation. 30KHz deviation (is that just under 25% or 50%?). No particular reason, just following old sparkIes comments 

Thanks,
Amie.

[Terry]

Full marks for spotting the missing diodes!

Not something you'd expect so not surprising that they got you so confused!

... the HF end of the band is weak though. I'll stop there, I won't want to mess it up in the name of perfection.

I entirely agree with resisting the temptation to do a full realignment just for the sake of it but it would be well worth finding a weak HF station and adjusting C36 for maximum - it should peak quite sharply and make a useful improvement in performance. It would be a pity not to make this simple check.

[pwdrive]

Just for info....Part of the FM ratio detector circuit forms part of the AM detectors diode load circuit.

Lawrence.