Symbol for IF transformer with tunable ferrite core

[Paul_VO]

For documentation purposes, I need to redraw badly drawn vintage schematics.
For the IF transformers, I can find symbols like TRANSF4 with iron core and ADT1-6T without any core, but instead of modifying these symbols, I wonder if a symbol is already existing for an IF transformer ?
After all, an IF transformer is a very frequent component in any vintage radio.
TRANSF4 comes closest, but I would need a dual dashed line to indicate a ferrite core, and an oblique line with a T-shaped end on it, diagonally over the symbol, to indicate the transformer needs to be tuned.

[djsbriscoe]

When you say “Vintage” what time period are you referring to? Does the schematic use transistors or tubes/valves?

[Paul_VO]

The schematics can include either transistors or tube. It is about heterodyne receivers with tunable IF transformers in one or more stages behind the mixer, for which I am looking for the correct symbol.

[djsbriscoe]

Is this any use?

[Paul_VO]

L1, L2, L3 and L4 are exactly the symbols I’m after… The ones after the respectively numbered ICs in the Revox B261 IF-stage schematic.

[paulvdh]

I recommend to just draw your own (or modify from an existing symbol). The first few symbols you make or modify take some time, but after a short learning curve you can do things like this in a few minutes, and that is quite possible quicker then searching for it or asking someone else.

[Paul_VO]

Okay Paul. Off she goes then…
Transformers-IF.lib (3.2 KB)
I found out from other threads in this forum (also threads by you) that I can specify smaller grids, which I needed for the dashed lines and the T-shaped end of the diagonal line.
The connection points were not touched and are still on the 50 mil grid.

[paulvdh]

Your TRANSF-IF-L looks like a well designed symbol.

I see you made a new one from scratch instead of starting from a (bigger / uglier) standard transformer. (I also added some other symbols for size comparison). It’s perfectly normal to put graphical items on a smaller grid, as long as the attachment points of pins are on a 100mill grid.

Is it common to hide pin numbers for these kind of transformers? It also does not have dots for magnetic polarity, is that an issue for this type of transformers?

During symbol design you can fill in the info in: Schematic Editor / File / Symbol Properties, and you can add a description and search keywords which makes it easier to find.

Edit: Just noticed it’s suspiciously similar to the 0868BM15C0001 schematic symbol

[Paul_VO]

I did not create it from scratch, but modified TRANSF4.
As the original schematic that I want to draw, does not include any dots for magnetic polarity, I did not add them.
Actually, there are even far more complex symbols for IF transformers, like in Saba radios:

Moreover, I found that the coil symbols can either:

• each individually have an arrow or a T-shaped line through them → adjustable inductance
• have one arrow or T-shaped line through both of the coil symbols → adjustable coupling
  (The symbol I modified, was for adjustable coupling)

In the Saba schematic, there are also no dots, but rather the ‘A’ and ‘E’ markings, and a tiny ‘o’ with a ‘T’ on top of it, probably to mark coupling. Today I opened a separate thread on the Saba forum to ask for clarification on these symbol elements.

And thanks, Paul, for your suggestions.

[paulvdh]

Just curious:

1. How much time did it take you to modify your first symbol?
2. How much time do you expect to take such modifications if you have done it a few times?

[Paul_VO]

Once I found out from other threads that you can increase the grid granularity, including your warning to take care the connection points have to stay on the default grid, it went rather quickly.

To create the ferrite core dual dashed lines, I first selected a grid of 5 mil.
First I selected the symbol TRANSF4 and saved it under a different name.
Then editing this TRANSF4, I selected the original core and deleted it.

I started by creating a single small vertical dash, and then duplicated it horizontally.
Then select this couple, and duplicate vertically, visually relocating so that the inter-spacing looks correct.
Select again the group of 4 lines, duplicate, relocate again below the previous group, and so forth.

Then create a diagonal line, and create a small T on top of it.

After saving the changes, I copied it again with a different name, and started editing.
Selecting the diagonal line, moving it aside, selecting the transformer symbol and mirroring it around the vertical axis to obtain the same transformer but with a split secondary winding.

The most important thing was to play with the grid
As you mentioned, now I can modify existing symbols in a matter of 15 minutes or so.
–With a little help from your friends–

[jmk]

Duplicate and mirror are best friends when creating transformers (amongst other things).

It is a shame that “Line Style” in Line Properties does not allow editing of the dash to gap ratios as it does in Schematic Setup > General > Formatting > Dashed Lines.

I should get off my posterior and add that feature request to the “Kicad Wishlist”