[Boatanchors] "Building" a Heathkit IT-28 capacitor checker

[Philip Atchley]

Hi,

Before you all get excited and say "Phil found an unbuilt kit", let me prick
your balloons with a pin!

A fairly nice looking IT-28 capacitor checker walked into the shop a few days
ago.  This is an item of test gear I've wanted for some time to help with
these old boatanchors, so you can imagine my joy 8^)

Anyway, I 'NEVER' plug an old piece of gear in until I've had it opened up and
examined it.  And this goes DOUBLE for Heathkits!  I'm glad I did.  Whoever
built it apparently didn't own a pair of wire cutters as all the parts,
resistors, capacitors etc were wired with full lead lengths still attached.
Many times the body of the component was right up next to the terminal lug
with an inch and a half of wire hanging out the other side in mid air.  You
can imagine what some of the soldering looked like.

So, I've been removing each and every part, one at a time, checking it, and if
good reinstalling it properly.  You might say I'm both "unbuilding" and
"Building" the unit.  I replaced ALL the resistors on the Voltage select
switch with new 5% units (A LOT of 10K resistors).  Originals were 10% carbon
and many just at the edge of tolerance on the high side. I also found a number
of other carbon resistors well out of tolerance (one 680 Ohm 1/2 Watt resistor
read 890 Ohms and a 100 Ohm resistor read 340 Ohms).

Anyway, this rewiring is "paying off".  It was obvious that this unit NEVER
worked from day one as BOTH filament leads to the eye tube were wired to the
same side of the 6.3 Volt filament line 8^(

The job is probably about 3/4 finished now. I "tacked" a silicon diode across
the rectifier tube and gingerly and slowly brought it up on the Variac (after
checking for shorts in the B+ line).  Even though I'll buy new filter cans for
it, I wanted to reform the old ones enough to do some further testing.  After
48 Hours of "forming I have full rated Voltage, the eye tube is lit and the
"Leakage" test section (3-600 Volts) calibrated OK.  HOWEVER, I have NO bridge
action on either the resistance or capacity ranges, so I suspect that there is
still a wiring error somewhere in the unit.  LUCKILY I DO have the original
construction manual!

Replacing those Voltage Range resistors with new 5% units paid off too.  As
you run the range switch through the 3-600 Volt settings the front panel test
Voltage is VERY close to what it says it should be.  The last one I saw had
some significant non-linearity's as you switched through the ranges.

By the way, this is an "E-place" item that was obtained for me (among other
things) as payment for some work I did.  I'm sure glad I didn't pay somebody
at the E-place a lot of money for it.



73 de Phil,  KO6BB
991 Different NDB's heard to date.

http://www.geocities.com/ko6bb/
Merced, Central California, 37.3N  120.48W  CM97sh