HW-8 IF transformer replacement

My cousin, Elmer, and lifelong pal KR3EP did some good old-fashioned horse-trading and, in the bargain, got his hands on a Heathkit HW-8.  He was kind enough to give it to me, so I started using it.  I instantly decided this was one of the perfect radios for me.  It's not too fancy, but it performs quite well.  It's one of the most-modified of radios, too, which means a lot is written about it.

This ad image was swiped from the web.  I'm old enough to recall the ad.

However, even though many people declare what they've done, very few show pics and explain the process.  So, when I realized that the 40m band had no signal at all, I decided to repair it and post the progress here.

This radio has excellent documentation online.  Google it up.  After some initial testing, I found that the 15.895 MHz crystal was getting the right voltage, yet was not oscillating.This crystal is mixed to produce the 7 - 7.250 MHz bandwidth when the "7 MHz" switch is pressed.  The diodes seemed OK, so I decided to follow the alignment procedure.  If you do this, OBTAIN THE CORRECT "twiddle" stick - a.k.a an "alignment tool".  You heard me.  USE THE RIGHT TOOL.  If one of your hands sneaks over and grabs a hex key, cut off that hand and put it, along with the hex key, in the trash.  DO NOT USE A METAL HEX KEY.  THIS MEANS YOU.

The little nylon hex adjustment tools are available to purchase on the Web, and if you want to fool with radios you really should have a set.  I purchased mine from eBay - the "Universal Color TV Alignment Tool Set - ST-13".  The seller shipped right away, so I had it in a jiffy. 

Some gomer in years past ignored this, and crushed the upper slug used to tune the 40m band.  It was stuck fast in the little cardboard tube and wouldn't budge.  So, I de-soldered it from the unit, along with its little metal shield.  The spot it came from is midway down the left edge.  There are actually six holes, since there are two for the lower slug wires and two for the upper slug wires and two for the shield.

The IF transformer is just a pair of wires on a cardboard form, with two adjustable ferrite slugs inside.

Also, you'll notice that I marked the "front" of the can and noted the way the slug-tuned inductor aligns with the board.  (The inductor has a mark also, hard to see).  It will save me having to figure it out from the schematic when I replace it.  If you look closely, you'll notice someone (probably the same person) slightly crushed the IF shield canister with a pair of pliers.  Doofus.  I'll call him "Ralph".  Don't be like Ralph.  If you want to use a hex key on a slug-tuned inductor or transformer, DON'T.  And if you crush the slug and decide to remove the shield from any old radio, de-solder the shield from the back side using a little solder braid.  DON'T CRUSH IT WITH PLIERS, IT WON'T COME OUT THAT WAY, RALPH.  Look closely at this picture, next to the hex nut mid-way down the right side of the frame, and you can see the hole where the IF transformer goes. 

The holes look burnt, but actually that's just old solder flux.  I'll clean it off later.

I contacted Earl Andrews up in Canada, who may be able to repair or maybe replace the transformer.  However, while I wait to see if I can restore the original part, I thought I'd experiment a little.  Calculations show that the lower inductor coil should measure somewhere in the range of 1.4 µH.  I measured this with my trusty LCR meter and found it to measure 1.390.  The lower slug was aligned to maximum voltage before I removed it, so that feels spot on.  The upper coil should be somewhere in the 0.771 µH range, but when I measured it I found 0.766.  So it's no wonder that the 40m crystal did not oscillate.

Thing is, we can go ahead and wind two inductors on toroid cores and solder them in just to see if we can get the radio working while we wait on the original inductor to be repaired.  So I'll do that and post the results here in a new entry.