[Boatanchors] Heath DX-100 modification information and othertransmitter service information

[lee]

Ray,

Besides the stuff below,  it would be a good idea to get rid of the two fuse 
plug inline with the power cord and install a single fuse holder under the 
chassis.  Not much room here but a fuse clip mounted underneath on the side 
panel works nicely.  (It's kind of a pain to remove the rig from the cabinet 
to replace the fuse, but it is much safer.  (There is little room for a 
bulkhead fuse holder).  When replacing caps, you can go larger in the audio 
chain and there are mods on line showing how to do this.  I would keep the 
filter caps near the same size as originals as ones too large can induce a 
"spike" in the audio chain upon key-up and really stress the modulation 
transformer.  I like to replace out of tolerance 1/2 watt resistors with new 
1 watt resistors as they are about the same size as old 1/2 watt resistors. 
It's a good idea to replace the silver micas in the VFO except for the NP0 
ones.  The VFOs have been known to "jump" frequency from bad silver micas in 
the VFO.  If you really want to splurge, replace the 50 watt bleeder 
resistor across the two caps in the 5R4  power supply.  This resistor has a 
center tap and is a 30K resistor.  So use two 15k 50 watt resistors in 
series so you wind up with a center tap.  If the old tapped bleader resistor 
goes out you can have a really unbalanced situation going on with the two 
filter caps in series.  Consequently they could blow if the bleeder goes 
out. (Two 125 uF @450 volt).  The audio driver circuits are really hard to 
get to.  I would advise just scraping everything in there and replace all 
the caps and resistors with new ones.  They all most likely would need to be 
changed anyway due to wanted audio mods or just because they are leaky or 
out of tolerance.  It would be much easier doing this then just trying to 
replace a few parts in this tight quartered section of the transmitter.  It 
would also be good to replace the Parasitic suppressors.  Use Ohmite OY 
resistors here.  I like the idea of using Computer grade 105C "snap in" 
capacitors held in with capacitor chassis clamps in the high voltage power 
supply.  The finished product looks good, the caps are first class and not 
expensive, and they are also insulated which is important as they are in 
series.  (You don't want to get across aluminum cans in series as they will 
have high voltage on the outside of the cans.  That's why Heath covered the 
aluminum cans with paper insulating covers).

I just rebuilt the lamp assembly which installs into the meter for 
illumination.  The heat of the lamp over time dried out the lamp wires and 
the plastic wire covering became brittle and caused the wires to get 
fatigued.  The wires were ready to break off.  I disassembled the meter lamp 
housing by pushing the "hot" wire forward toward the front of the lamp 
holder.  The lamp holder has a small brass center pin which looks like a 
brass rivet.  the wire is soldered to this pin.  To keep the pin and wire 
centered within the housing there is a small fiber insulating insulator 
around the brass center pin.  Heat had destroyed this insulator and as I 
pushed the pin out of the housing, the insulator just crumbled into dust.  I 
fixed all this using one half of a TO-220 bolt insulator.  One of thee bolt 
insulators has two halves for the bolt to pass through.  I used the half 
having a small lip on it.  The brass center pin of the lamp assembly fits in 
this insulators hole perfectly.  I had to take a small file and reduce the 
diameter of the fiber TO-220 insulator slightly so it would pass down into 
the lamp assembly well with no obstruction.  It just took a couple minutes 
of filing to accomplish this task.  I think I will replace the lamp in this 
assembly with a new modern LED version of the appropriate incandescent lamp. 
The heat reduction should keep the destruction from reoccurring in the 
future.  This fix of the lamp assembly really worked out well.

Hope some of this helps with your restoration.  I love DX-100s!!

Lee, w0vt




Subject: Re: [Boatanchors] Heath DX-100 modification information and 
othertransmitter service information

Ray,

The B model had the newer smaller/lighter cabinet, the nickel plated
chassis, and was pre-punched for the SSB adapter mod needed to use their SSB
adapter on a DX-100.  It also had the latest totally variable loading
capacitor without the switch and fixed cap scheme in the earlier version.
Today, one sometimes adds a spot switch, broader audio response mods, maybe
solid stating the power supply (mixed bag), and sometimes allowing the VFO
to run constantly when operating CW but I don't like this mod.  There are
other mods one could do such as add a third 6146 to the rig, but I would not
do this as it would be hard on the transformers and screw up the tank
circuit Q.   A worthwhile addition would be installing a neutralizing wire
in the transmitter.  That's about it.  There was not much difference between
the earlier version and the later one.

Lee, w0vt