Quote:
Originally Posted by dtvmcdonald
The RF design of the TRK-12, while generating absolutely beautiful
frequency sweeps, is an ABYSMAL design that the engineers
MUST have known had coils and wire that were FAR too big.
When the band changes happened, they had to rewind the coils,
and it wasn't pretty. My set was never sold, being apparently used
as a test bed for changes by the RCA engineers, and it has
rather klunky looking change places. Maybe they though that bigger coils would have better Q.
And oh yes ... the fine tuning barely has enough range to tune the FM
signal acorss the split carrier IF discriminator over 200 kHZ!
Yet the final response at the video detector output is identical
to that of a properly tuned CT-100.
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Doug,
Just to clarify, I believe you are referring to the oscillator coils in the tuner and not the IF's. I don't want people thinking RCA rewound IF's or anything else.
The changes that created that "mess" in the tuner LO section cannot fully be blamed on the engineers or on the original design of the set. The sets were designed for the original channel assignments and if you look at a set that has not been modified, they are clean and sweep extremely well. When presented with the change, the engineers did the best they could. The fact that the channel order had to be swapped from low to high to high to low (requiring those black channel labels) could not have been easy for the engineers, but was a clever solution. I have been faced with similar challenges many times during my career and you don't always end up with a solution you are fully happy with, or proud of, but such is engineering. You rarely get everything you want and make the best of what you have.
The narrow fine tuning of the RCA pre-war sets compared to every other manufacturer also puzzled me at first, but I have to give credit to the RCA engineers that their sets, when fed with a proper AM audio signal, never need trimming by the user. Their LO stage is just that stable. The other manufacturers, mainly GE and Dumont, do require the fine tuning to be touched up periodically by the user, which may explain why they are so wide on these sets.
Darryl