[Hallicrafters] HT-37 Alignment "Lessons Learned"

[Rocco Lardiere]

Bill,

Pat's suggestions are excellent.  That capacitor could very likely be the
problem if the inductor is ok.

Here are some hints if that does not work (these are not for the weak of
heart or technically challenged).

Use DeOxit on suspect contacts FIRST (and sparingly).

I would add that bandswitches can (and have) become slightly misaligned in
many of the boatanchors I have gone through.  If you are suspicious of a
switch section, take out your magnifying glass and look very, very carefully
at the moving, flat switch contacts as they sweep through the "pincher"
stationary contacts.  On your transmitter, this would be the contact that
connects to the coil and capacitor.  Often, you will find that there is a
slight rotational misalignment of the wafer with respect to the rotating
shaft contacts that results in the flat contacts not being exactly centered
between the spring "pincher" contacts in a detent position.  No amount of
DeOxit can fix this if the misalignment is bad enough.  Sometimes the screws
that retain the entire outer wafer section need to loosened to correctly
align all the wafers' contacts correctly with respect to the shaft and
detent.  The trick is that the wafer holes for the retaining screws are
usually a bit oversize, and a chosen "bad boy" outer wafer can be
individually realigned to where it should be by using up some of the
rotational slop in the wafer screw holes.

Retighten the screws once the wafers have been slightly twisted back into
alignment.  ALL the wafers on the long shaft need to be correctly aligned
for ALL detents.  Long bandswitch wafer chains such as on the HT 37 and many
other Hallicrafters transmitters and receivers are prone to this type of
problem, especially if someone has been in there in years past.  For basket
cases, beware that someone may manage to rotate an inner wafer 180 deg and
then replace the shaft - looks ok - but that will kill the operation of the
unit.  I saw that on an SX 115, once.  It worked much better when rotated
back into position!

I have seen misaligned wafers many times in other Hallicrafters gear, and
it's easy to fix once you recognize it.  Just be careful not to damage any
switch contacts - they are very, very delicate and REALLY tough to replace
once damaged.

This may not be your problem, but when someone has switches that don't quite
work unless you wiggle the knob around the detent or don't work at all, it's
something to check if DeOxit does not clear the problem.  It can also "fix"
a badly worn bandswitch, sometimes - by moving to a less used portion of the
remaining flat rotating contact surface.

73,

Rocco N6KN

----- Original Message ----- 
From: "Patrick A. Thompson Sr." <wa4tukhr at comcast.net>
To: "Bill Pancake" <bpancake at mindspring.com>
Cc: <hallicrafters at mailman.qth.net>
Sent: Sunday, August 29, 2004 4:41 AM
Subject: Re: [Hallicrafters] HT-37 Alignment "Lessons Learned"


> You should trace the circuit through the bandswitch and look for open or
> burned switch sections. One or more of the rivets may have let the
> switch fingers open up.
>
> The manual says that L23 is used in conjunction with C74.  You might try
> replacing C74 or replace it briefly with a small trimmer. It looks like
> 200pf with 2% tolerance on the "BAMA" schematic.
>
> Good luck!
>
> Pat
> wa4tuk
>
> Bill Pancake wrote:

> . . .

> >I started to align it using an HP 606A rf signal generator and HP 410b
VTVM following the procedures in the factory manual. The driver and 2nd
mixer stages aligned as per manual. The 1st mixer 40m coil (L23) will not
cause a PA grid voltage peak on the VTVM as it is adjusted like it is
supposed to.  Now I'm dead-in-the-water.  Since I can't align the 1st mixer,
I can go no further.
> >
> >>From those of you who have experience with HT-37 alignment, I'd almost
sell my soul for a suggestion on what's wrong with the 1st mixer stage. L23
(40m coil) has good continuity and circuit wiring for that entire stage
appears to be wired correctly.
> >
> >If there are other "lessons learned" in aligning an HT-37, or if I've
missed a key procedure, please pass them on. There's no question in my mind
that I'll take your advice if it's offered. . .
> >
> >> >
> >Thanks, Bill, ab0zz
> >
> >
>