04-29-2022, 01:49 PM
Hello everyone,
Readers of the Phorum may recall that I had a problem with this radio -the ferrite cores in the tuner had come adrift through age from the "push bar" and were moving randomly.
As mentioned in the previous post,I had hit on the idea of locating very small brass nuts in the push bar in a blob of RTV ,similar to how some suspension components in cars are located in nylon or plastic bushes,though on a much smaller scale.
This idea seems to have worked.
Those of you familiar with permeability tuners will know that the cores are more or less in line when working , each of the three being roughly a similar distance from the pushbar. The devil is in the detail,particularly in regard to the oscillator core. Once introduced into the brass nuts ,though, the cores could be wound in and out fairly freely and I discovered in my set of aligning tools a tool which engaged perfectly with the flattened sides of the ends of the brass rods.From there aligning was fairly straightforward.
I set the pushbar using the dial pointer to about the position for 750 kilohertz and connected the signal generator ,set to 750 kilohertz to the aerial.The signal tracer was connected to the grid of the r.f. amplifier and that core peaked. Similarly the signal tracer was connected to the grid of the converter and the other core peaked .Knowing these circuits were now in tune , tweaking the oscillator core (the one in the middle ) to get the i.f. signal , was simple with the signal tracer connected to the grid of the i.f. valve and the i.f.signal peaked there .Some further fine tuning is required but across the band there seems to be a pleasing linearity.
I will mention one hiccup which occurred which may be of help to Phorum readers. During the rather physical manipulation of the radio during these proceedings I was horrified to discover that one of the up- till- now intact cores had broken just below the point where the brass rod entered the ferrite. Oh no! Where will I ever get another? That's the end of this restoration! Well, I fished the two bits out. The break looked very clean . There's nothing to lose here - glue it back together and see if uniform inductance can be restored through superglue.So far it seems it can and linearity,as mentioned above seems okay.
I'm pleased to have got this set going. Some posts suggest this set comes from a Ford Thunderbird.It seems to represent ,to me . the pinnacle of American valve car radio engineering with 6AQ5 push pull output and great sensitivity.Equipped with a New Zealand made electronic vibrator it goes well,though the current demand it makes on my bench power supply suggests that the imminent change to twelve volt systems in American cars can only have been timely.
If anyone has suggestions for other ways of going about solving these problems with tuning I'd be pleased to hear. Cheers everyone,
Readers of the Phorum may recall that I had a problem with this radio -the ferrite cores in the tuner had come adrift through age from the "push bar" and were moving randomly.
As mentioned in the previous post,I had hit on the idea of locating very small brass nuts in the push bar in a blob of RTV ,similar to how some suspension components in cars are located in nylon or plastic bushes,though on a much smaller scale.
This idea seems to have worked.
Those of you familiar with permeability tuners will know that the cores are more or less in line when working , each of the three being roughly a similar distance from the pushbar. The devil is in the detail,particularly in regard to the oscillator core. Once introduced into the brass nuts ,though, the cores could be wound in and out fairly freely and I discovered in my set of aligning tools a tool which engaged perfectly with the flattened sides of the ends of the brass rods.From there aligning was fairly straightforward.
I set the pushbar using the dial pointer to about the position for 750 kilohertz and connected the signal generator ,set to 750 kilohertz to the aerial.The signal tracer was connected to the grid of the r.f. amplifier and that core peaked. Similarly the signal tracer was connected to the grid of the converter and the other core peaked .Knowing these circuits were now in tune , tweaking the oscillator core (the one in the middle ) to get the i.f. signal , was simple with the signal tracer connected to the grid of the i.f. valve and the i.f.signal peaked there .Some further fine tuning is required but across the band there seems to be a pleasing linearity.
I will mention one hiccup which occurred which may be of help to Phorum readers. During the rather physical manipulation of the radio during these proceedings I was horrified to discover that one of the up- till- now intact cores had broken just below the point where the brass rod entered the ferrite. Oh no! Where will I ever get another? That's the end of this restoration! Well, I fished the two bits out. The break looked very clean . There's nothing to lose here - glue it back together and see if uniform inductance can be restored through superglue.So far it seems it can and linearity,as mentioned above seems okay.
I'm pleased to have got this set going. Some posts suggest this set comes from a Ford Thunderbird.It seems to represent ,to me . the pinnacle of American valve car radio engineering with 6AQ5 push pull output and great sensitivity.Equipped with a New Zealand made electronic vibrator it goes well,though the current demand it makes on my bench power supply suggests that the imminent change to twelve volt systems in American cars can only have been timely.
If anyone has suggestions for other ways of going about solving these problems with tuning I'd be pleased to hear. Cheers everyone,
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