I’ve been seeing a few posts lately on people needing to rewind certain coils. I thought I had read somewhere, can’t remember where, that for antenna or RF coils, the direction you wind them cw or ccw, doesn’t matter. Oscillator coils do matter because if wound the wrong way there is no feedback and no oscillation. I recently had to rewind the primary of a RF coil on my Philco 70 and so didn’t take notice of the direction but it works or did I get lucky? Am I missing something? Thanks for any input.
Ron
Complex question, you have not reversed the way it is hooked up, (I can see that making a difference due to opposite phase currents through the chassis and subsequent stage), you just possibly wound in reverse. It would be a study of the magnetic coupling fields built up on each winding - one way vs. the other, and also how the shielding cans affect it. Probably won't notice much in the 70, but never know, winding in opposite might affect the quality of the transformer.
An RF or an AF transformer can be used to invert the phase of the signal by 180 deg. If such an inversion is made to a circuit, the circuit could oscillate or degenerate. Depending on how the design of the stage is using that transformer.
Some restorers of 20's era battery sets have found this to be true with the audio transformers. For example some reflex receivers must have the 180 inversion or the set will oscillate uncontrollably. Other radios with an audio transformer that has a common core and two bobbins each, a primary and secondary must be "phased" properly or the AF amp becomes an audio oscillator.
IMHO such an inversion in an RF or IF coil may cause a similar oscillation issue. IMHO it is better to pay attention to winding direction and circuit connection rather than have to guess and make transformer wiring swaps, which may not be practical because of physical layout.
YMMV
Chas
It was discussed several years ago; I am still not sure I fully understand how inverting the direction of an RF coils in non-feedback type stages affects anything at all. Oscillators and such are different - they specifically depend on the phase of the signal for the feedback, but a regular RF xfomer should not matter. No more than a "banded" end of a tubular non-polarized cap matters in most situations (it does not).
Then again, it always better to follow the schematic and the factory hookup, if only to avoid mystery problems.
Thanks guys. I was only talking about antenna/RF coils. I understand about audio transformers as many sets use some type of negative feedback to help with distortion, thus phasing is important or else the set may oscillate. Mike, I was thinking the same as you so I didn’t take note of direction when I rewound the coil in my 70. After seeing some of these posts where it was said to rewind the same direction and even in the Radio Library, that is what has me questioning the procedure! I did keep the terminals the same, B+ to B+ and plate to plate, just didn’t pay attention to direction.
Ron
The only reason I can think of for winding antenna and RF coils in the original directions is that in some cases the phasing of the windings may be important. This is because certain coils may be designed with both inductive and capacitive coupling between the windings.
Some antenna coils have an extra turn or two of unterminated wire from the top of the primary wrapped around the hot end of the secondary. This wire provides a small amount of capacitive coupling to the secondary and was done to increase the signal transfer at the high end of the broadcast band where the sensitivity would tend to drop off.
So, when both windings were done in the correct direction, the current induced in the secondary is in phase with the current coupled by the capacitance and add together constructively. If one winding is done in the opposite direction, the two currents will be 180 degrees out of phase and will subtract, causing a loss of sensitivity at the high frequency end.
In any case, if possible it would make sense to try and rewind the coils exactly as they were originally.
Hi Mondial, I’ve seen sets with that gimmick winding and understand the need to keep phasing the same. As for some stray capacitive coupling, I would think as long as the physical end of the rewound coil going to the plate of the RF amp for example is kept in the same position as the original, it should work. In the future, I am going to try and determine the direction the original was wound and keep it the same! Thanks for your input!
Ron