|hamelectronicsmagazine.com - May 2015
|A short article about Slug Tuned Coils - this one was
from an FT301 circuit board but this applies to other
slug tuned coils as well.
|Just the other day a fellow in USA wrote me for a
spare circuit board.. (the RF Unit). He wanted some
parts off of it to fix his ailing RF Unit - FT 301
I am looking for a FT301 RF UNIT in working condition or for
parts. The unit I have has the T-101 tuning core missing.
Seems that the Slug tuned coil had its slug broken.
He later wrote me again --
. On the Trimmer Unit PB-1446 the coil or transformer T1401
has also its tuning core missing. Can you spare one for me?
I didnt have a good working spare RF Unit but I sold
him one with a slight problem or two. I charged only
$18 plus I sent him another part for free (shown to the
left in the picture - a slug tuned inductor off this other
board for FREE and I sent him a sample DG mosfet as
This is typical of my services. I charge very
reasonable prices for parts and my labour is only
$10/hr -- RETIRED HOBBY RATES (I'm semi retired).
|Above pictured is the Trimmer Unit PB-1446 that I have parted out.
I have quite a few spare boards and parts for the FT301.
I learned a good lesson from this-- TEST THE COIL to make sure it is
good and not damaged or burned out or something.
I took the coil apart as shown above and found the winding was
Im not sure how it happened !! -- SEE picture below.
|This coil on the trimmer unit is a shielded coil - single winding of around .5 uh and variable. Did I damage it by breaking the wire when
I was prying off the metal can? - I dont think so. -- The T101 inductor on the RF board is similar to this one. A single winding and not
really an RF transformer.
SO ..IF YOU ARE REPAIRING A RADIO and have problems getting the tuning to work.. dont assume that the coil is good. MEASURE THE
WINDING WITH AN OHMETER to see if it is indeed not broken conductor.
IN THIS CASE..THE FELLOW IS JUST REPLACING THE SLUG -- but the coil could be repaired with a bit of care.
IF the coil is too far gone-- ie the slug is crumpled up or something.. I would imagine a small toroid core wound to .5 uh could be used.
A T37-6 is what I would use with fine enamelled wire. I would move the windings to resonate the circuit then use some good clear nail
polish or something (I have the proper Q DOPE here in my shop).
|Above.. I use this nifty test instrument I bought from Ebay for around
$30 - Measures inductance, larger capacitance values, ESR of
capacitors.. a very useful tool.
73 earl ve3ab