04-04-2016, 07:50 PM
(This post was last modified: 04-04-2016, 07:51 PM by Geordie McBoyne.)
Now that the Eddystone 670A is working as it should I've turned my attention to a slightly earlier receiver, the model 659/670.
Unlike the 670A which was found to be in an unmolested condition this set has well and truly been got at by someone in the distant past. The original tapped mains dropper resistor has been replaced by a single 600 ohm resistor, the correct total value should be 500ohms. Note the PL259 aerial socket which replaces the aerial and earth sockets., I'm sure those parts and modifications were not sanctioned by Eddystone. A silicon diode replaces the finned metal HT rectifier.
For starters I found valves in the IF and audio stages in the wrong positions, some valves were glowing brightly and others not lit up at all.
After refitting the valves in the correct positions I found only two of the four wavebands were working, band 4 246 to 575 metres and band 2 5.8 to 13 Mc/s. Band 3 1.2to 2.75Mc/s was completely silent. Band 1 12.8 to 30Mc/s just produced a hiss and funny noises.
Waveband 3 turned out an easy fix, the aerial input coil had been shorted out for some unknown reason, removing the short circuit brought in the signals. Whereas the 670A does not tune to the Radio Tyneside station on 1575Kc/s the 659 can do this easily because Waveband 3 extends into the HF end of the Medium Waveband.
The IF amplifier was found to be spot on at 450Kc/s so at least no twiddling there.
Wavebands 2,3 and 4 were easy to realign, problems with waveband 1 though. It is possible to trim up the lower frequency end of the band the HF end will not line up properly at all. The reason for that might possibly be that the valve heaters are under run, as mentioned before that mains dropper is the wrong value, it's 600 ohms and according to the service manual it should be 500 ohms. The UCH42 has a 14 volt heater and the voltage measured across pins 1 and 8 is 11.5V. An under run valve may not work at the higher frequencies.
To sum up the work done so for, the set works very well on Waveband 2,3 and 4, it's waveband 1 that is causing problems.
The attachments show the receiver, the mains dropper resistor and that PL259 aerial socket.
Geordie McBoyne.
Unlike the 670A which was found to be in an unmolested condition this set has well and truly been got at by someone in the distant past. The original tapped mains dropper resistor has been replaced by a single 600 ohm resistor, the correct total value should be 500ohms. Note the PL259 aerial socket which replaces the aerial and earth sockets., I'm sure those parts and modifications were not sanctioned by Eddystone. A silicon diode replaces the finned metal HT rectifier.
For starters I found valves in the IF and audio stages in the wrong positions, some valves were glowing brightly and others not lit up at all.
After refitting the valves in the correct positions I found only two of the four wavebands were working, band 4 246 to 575 metres and band 2 5.8 to 13 Mc/s. Band 3 1.2to 2.75Mc/s was completely silent. Band 1 12.8 to 30Mc/s just produced a hiss and funny noises.
Waveband 3 turned out an easy fix, the aerial input coil had been shorted out for some unknown reason, removing the short circuit brought in the signals. Whereas the 670A does not tune to the Radio Tyneside station on 1575Kc/s the 659 can do this easily because Waveband 3 extends into the HF end of the Medium Waveband.
The IF amplifier was found to be spot on at 450Kc/s so at least no twiddling there.
Wavebands 2,3 and 4 were easy to realign, problems with waveband 1 though. It is possible to trim up the lower frequency end of the band the HF end will not line up properly at all. The reason for that might possibly be that the valve heaters are under run, as mentioned before that mains dropper is the wrong value, it's 600 ohms and according to the service manual it should be 500 ohms. The UCH42 has a 14 volt heater and the voltage measured across pins 1 and 8 is 11.5V. An under run valve may not work at the higher frequencies.
To sum up the work done so for, the set works very well on Waveband 2,3 and 4, it's waveband 1 that is causing problems.
The attachments show the receiver, the mains dropper resistor and that PL259 aerial socket.
Geordie McBoyne.