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Heathkit DX 100B
Mod

Here is an easy modification to do
to see what your actual transmiting frequency
is on the Heathkit DX 100 B Transmitter without going on the air .


by N8ITF


The reason for the modification was so that I could see the actual multiplied frequency of the VFO before I put the rig on the air and the other reason was that because of my failing vision it was easier to see the frequency counter than the VFO dial .

So I studied the schematic and found because of this transmitter being a class B plate modulated transmittrer that this was an easy task to do and when done you should see the frequency displayed without it being effected by the modulated B+ to the final amplifier in the transmitter .

Please note this mod can be done to any transmitter as long as you remember to make sure that the connection to the frequency counter is decoupled by a very small value disc ceramic cap , so that you will not loose a great amount of RF feeding the final amplifier stage of the transitter .

And the reason for this is , when you go to 15 or 10 meter bands you will find that if you use a large value cap anything above 5PF. , the output power of the transmitter will be reduced .

So to have the same output power at the antenna you will need to use a 5PF. cap to reduce the coupling to counter .

When this mod is done you will be able to see the transmitting on the frequency counter in the CW position when you depress your cw key , without appling B+ to the final amplifier stage or going on the air .

So here we go ....



Unknown Bonus's of the modification ...


Parts required for this mod .

1 - 5PF. 1KV disc ceramic cap
1 - Chassis mount BNC Jack or whatever jack you desire .
1 - 22" inch piece of RG-58A/U coax

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Warning

Be very careful when removing the transmitter from its case . The 6au6 VFO tube is right next to the top of the case and can be broken if the chassis is not pulled straight out , and NOT on an angle .

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This a picture of the 12BY7 and 5763 compartmnet .




Mounting the BNC




Securing the coax .


This is the back of the transmitter and I used a piece of alumimun tape to cover the SO-239 Jack hole to prevent those " poor little mouses from killing themselves " and causing any further damage to the transmitter .


This picture is an overall view of the bottom of the transmitter to show you how I ran the coax .