Wednesday, February 8, 2017

Waiting for disk tool test time, meanwhile restoring a Heathkit HW-100 ham transceiver


All is ready for testing but I have to get to Marc's house to do this, which means a couple of days of waiting.


I pulled out a HW-100 that I had bought a few years ago with the quixotic intent of converting it into a kit (desoldering everything, buying new components for all resistors, capacitors etc) and then building it 'as if' I had bought the kit way back when.

Heath HW-100 SSB Transceiver

I actually have many of the replacement components but have changed track. At this point, given how nicely it appears to have been built, I will simply restore the unit to operation and align it carefully. In order to do this, I need to buy the power supply, which was an external unit called an HP-23A/B/C that furnished the 800V, 300V, filament and other power needed for the transceiver itself.

Inside the HW 100

I opened it up and began checking out the vacuum tubes inside. I know that several of them are quite rare and very pricey to buy, such as the 6GW8 audio amplifier tube. Of the 20 tubes that are used in the unit, 18 were in place and astoundingly, every one of them tested good. The only two that are missing are pretty common and reasonably priced tubes - a 6AU6 and a 12AT7.

Testing the vacuum tubes

I found that the electrolytic capacitors inside the unit had been replaced by a previous owner, thus were modern and safe substitutes for the originals that would have been dangerously aged. Of course, I still need to deal with the big electrolytics coming in the HP23 power supply, but this unit is in good shape.

There are three rubber belts which turn variable capacitors to tune and load the RF sections, which had turned to brittle material and already snapped in one case. I have bought a replacement set on Ebay. I am also ordering the two missing tubes so that I can be ready to move forward when the rest of the testing and restoration is complete.

Cracked and broken rubber belts needing replacement

I will go through the unit and check out components, to the maximum possible extent without unsoldering them. The high impedances of vacuum tube components makes this more feasible than with low ohmage solid state components.

Until I have the power supply in hand, restored and checked out, I can't actually check out the operation of any part of this. I will need a dummy load before I can test the transmit functions and should have some sort of an antenna to test reception. 

No comments:

Post a Comment