Friday, February 10, 2017

Preparing for modifications to HW-100 and testing key components


I accompanied a friend who was inspecting some tape drive equipment for possible purchase. These were two 3420 model 6 drives (9 track reel to reel, 75 inch per second, at 1600 and 6250 BPI) plus the 3803 model 2 controller. They were in surprisingly good condition and he will be buying them. 

He has to arrange for a trucking company to go to the site, pick them up and bring them to his home about 100 miles away. These will join the single 3420 mod 6 he already owns. 


I located some recommended modifications for the unit - then checked to be sure that none were applied on the unit already. I will collect the parts and make the changes over the next couple of days, while I am waiting for the two missing tubes and for a power supply.

I also picked up a Direct Digital Synthesizer VFO unit that will replace the Heath supplied VFO, to provide for much higher frequency stability as well as offering split mode and RIT features.


I received a V-7 (late 1950 era) Vacuum Tube Voltmeter which is able to handle nice high voltages (up to about 20KV) and has 11 Megohm input resistance to avoid dragging down the measured circuits. I inspected it, plugged it in and switched it on. Nothing. No sign of life.

Some quick diagnostic work showed that the defective component was the line cord from the wall socket. One of the prongs on the plug had no connectivity through to the wire as it mated with the circuit board inside. No, this is not a fused plug, it is just a complete and total break somewhere in the cable, with no visible signs of damage to be spotted.

The solution is a new cable, where I will implement a three prong plug and ground the chassis for the protection that was missing in the 50s era design. 

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