[Hallicrafters] SX101A and HT37

[W4AWM at aol.com]

Hi Andy,

I have an HT-37 also but have not had time to restore it. I am told that the 
only problem is with the bias circuit and I suspect it has something to do 
with the selenium rectifier that is supposedly used in the bias supply.  I have 
not had it out of the cabinet yet, just another winter project that I will 
never get to.

I am told that the main weak point in the HT-37 as well as the HT-32 is an HV 
to rectifier filament winding short in the power transformer.  The easy fix 
for this is to solid state the power supply which is not difficult to do.  It 
is also prudent to remove the filament leads from the transformer that run to 
the rectifier tube socket.  This accomplishes 2 things.  It keeps the HV off 
the filament windings and it reduces the heat buildup in the power transformer 
since it no longer has to light the rectifier.

The next thing to do is check the voltages since they will run higher with 
the solid state rectifier. Also, check your incoming line voltage.  If it runs 
more than a volt or 2 higher than the rated input in the specifications, you 
should either run the rig on a variac or build a bucking arrangement to lower 
the input voltage to specs. You should probably look into this first before 
checking the high voltage since if the input is high, so will be the output.

Speaking of input voltage, now is a good time to replace the cord set with a 
3 wire unit. Be sure to wire it so that the fuse is in the hot (black lead) 
side of the power cord.

If there are any black beauties in there, pull them out.  They are nothing 
but big trouble.Also, as you mentioned, change anything paper or electrolytic. 
If it isn't giving you trouble now, it soon will be.  Look carefully at the 
resistors and change anything that looks suspicious.  I have a lot of large 
resistors around the shop and will generally replace anything that needs it with 
the next highest wattage as long as there is physical space available.

Those are the basics.  There are a lot of fellows on here with superior 
knowledge to mine, so don't be afraid to draw on their experience, too.

73, happy holidays and keep one hand in your pocket.

John,  W4AWM


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