[Elecraft] Trouble With Toroids

[Tom Hammond]

Hi treat:

>Can someone enlighten me as to the proverbial problem that seems to come 
>up with torriods? Just build a K1 and found the torroids straightforward 
>to wind, strip and tin. The unit fired up flawlessly. Maybe it's because 
>I'm a sailor and found winding torroids an awful lot like whipping line 
>(wrapping small twine around the end of rope so it doesn't unravel). 
>Beginner's luck on my part? Or am I missing something?

Truthfully, and as you've already discovered, there's NOTHING difficult 
about winding toroids, but many first-time 'winders' approach the thought 
of winding their own cores with quite a bit of trepidation...

  1) They worry about whether the turns HAVE to be perfectly spaced.

     The simple answer is "No they don't", but if you're gonna be
     showing off your finished 'baby' to others, you will want the
     quality of your workmanship to be evident in cleanly-wound
     inductors, where the turns are relatively evenly spaced and
     (following the instructions in the manual) spaced to occupy
     80%-90% of the entire available core, AND that they're wound
     in the proper 'sense', with regard to the direction of the
     winding of the turns.

     Toroidal inductors which have the requisite number of turns,
     but on which the turns aren't well-spaced, may exhibit a
     slightly different inductance, but generally NOT to the point
     that it will make a significant difference in the performance
     of the radio.

  2) They worry about accurately counting the number of turns.

     This IS an important point. You MUST apply the required number
     of turns to the core... no more, no less (unless required to
     do so as a result of other value variations within the circuit),
     and this usually involves only one (1) single turn added or
     removed.

     Each time the wire goes THRU the center hole of the core,
     counts as ONE TURN. Even if you just stuck the wire thru the
     core and soldered it on each end to the PC board, that's still
     ONE TURN. When I wind toroidal inductors, I usually kinda
     'muck up' the first turn laid on, so I'll usually wind a couple
     extra turns, count the total turns applied, and remove and
     extra turns from the 'front' of the coil, so any boogered up
     turns are removed. I ALWAYS count turns once I've completed
     applying them to the core.

  3) They worry about being able to adequately strip and tin the
     inductor leads.

     This is also a VERY IMPORTANT point. Fully 75%-80% (maybe more)
     of the Elecraft service problems sent to Gary Surrency (AB7MY),
     Elecraft's Chief Tech, result from PTTLs (Poorly Tinned Toroid
     Leads). Some builders seem to get in too much of a hurry to
     tin the inductor leads and, as a result, wind up not doing a
     suitable job of removing the enamel and thus not getting a
     well-tinned lead.

     There are numerous methods of stripping and tinning toroid
     leads, and I'm not about the start another (almost religious)
     thread on the 'best' method to use. Suffice it to say that,
     properly done, ANY of the recommended methods WILL produce
     nicely tinned inductor leads, suitable for your Elecraft kit.
     However, it only takes one single PTTL to mess things up to the
     point that a LOT of troubleshooting may be required to fix a
     problem which should never have occurred in the first place.

     Another important point is to ensure that you tin the lead
     all the way up to the core, so that when the lead is pulled
     tightly within the PC board hole (ready for soldering) you
     have not managed to pull un-stripped wire down into the hole
     where it will not produce a good solder joint.

     Like they say, "There's never enough time to do it right, but
     always more than enough time to do it over".

  4) They worry about how to mount the toroidal inductors so they'll
     be solidly affixed to the PC board and not 'flop' around.

     Fortunately, with the K2, this is not a terribly significant
     problem as there are only a couple toroidal inductors which are
     in sensitive frequency-determining circuits and these inductors
     are pretty easy to mount securely.

     The toroidal inductors which are mounted vertically, and there
     are a number of them, DO NOT have to be affixed TO the PC board
     with glue or other fixatives. If they are installed properly,
     by their leads, they will be securely installed and will require
     no further attention. When I install toroidal inductors
     vertically, I stick their leads thru the PC board, bend the
     leads slightly, to hold the core in place, and solder each lead.
     THEN, I go back, grasp each lead with a pair of needle-nosed
     pliers, exert a light pull on the lead WHILE reheating the
     soldered junction. This allows me to remove the last bit of
     slack which might have crept in while I was doing the initial
     soldering of the leads.

  5) They worry about wearing out their fingers while winding.

     Can't argue there. Winding toroids, especially of you work to
     ensure that each turn has been laid on tightly and smoothly,
     can tend to make your fingers a bit sore.

     I've found that if I 'form' the wire around the outside edges
     of the inductor core before I lay on the next turn, when I do
     lay the turn on, it will readily conform to the pre-set bends
     and it will not require nearly as much pulling and yanking on
     the wire. Resulting in less finger fatigue.

That's about it! Winding toroidal inductors CAN be difficult IF you make it 
so. But then again, it doesn't have to be. It does take some care in 
winding, but then this is a radio you WANT to take care with, so you'll be 
proud of the end result... so it's worth the effort.

73 and happy winding.

Tom Hammond    N0SS