Saturday, February 18, 2017

HW-100 power supply restored, disk tool archiving packs correctly


My copy of Contralto was corrupted, but when I reinstalled it, I was able to take the cartridge image I had uploaded using my disk tool and boot it up just fine. Whatever problem is keeping cartridges from booting, it does not impair the reading capability.

While we took traces from the logic analyzer yesterday, they are formatted oddly compared to the way we traced prior reading attempts. As a result, I am having difficulty following them to see what is different between booting one of the cartridges I wrote and others that work fine.


My update kit for the HP-23 power supply arrived today, I assembled it and installed it into the unit. I then tested the unit to check that it produced the +800, +300 and 130V DC as well as filament power. While it also generates an adjustable bias voltage, that is not used with the HW-100 receiver.

HP23 Power Supply as received
Original parts inside (plus big filter capacitor cans)
Parts stripped out and ready for new circuit board

Soldering the board itself was easy, but getting all the loose wires from the chassis to the proper points on the board was more devilish. One of the wires was just too short to reach the hole on the board, yet it was the 800V transformer output which I really didn't want to splice. 

I ended up with no choice in the matter, thus I had to put in a join on a spare terminal strip. There were issues with ground connections that required some improvisation. Finally, the original RF filters on the input were gone but the wiring had to be restored to stock connections between plug, power lamp, power switch, transformer and the AC switching pins on the connector that runs out to the transceiver. 

After this was all done, I double checked the wiring against the schematics to be certain it was right. Some careful comparisons, continuity, resistance checks and other tests were performed before I would allow power to flow in the supply. 

New PCB visible under holes from removed filter capacitors
Plug in, switch on and I measured everything on spec. A bit over 800V for HV, over 300V for LV, under -130V for fixed bias, about -80V for adjustable bias, 13+ for the 12V filament supply and 6,5V for the 6V supply line. The unit is ready to go.

Restored and updated HP-23 power supply

To do the testing, I used my recently restored V-7 Vacuum Tube Voltmeter. One reason I got it was to measure the relatively high voltages in old tube equipment.

V7 VTVM ready for use
When I received the power supply, it was mounted inside the Heathkit SB-600 speaker enclosure. It was cheaper to buy the power supply WITH the speaker enclosure than to buy one along - and I have a speaker to use with the transceiver as well. Needs a bit of cleaning on the paint job and some dings handled, but otherwise is fine.

Dusty, dirty and dinged speaker cabinet


  1. I've lost the thread here... what is the "new pcb"? Did somebody actually design and sell a new circuit to update the old Heath power supply? Also, what replaces the four old giant electrolytics? Are modern capacitors really that much smaller and more efficient?

  2. Also, looking at the rust, I'm thinking, OK, a museum would leave it alone, but if it was my personal restoration, I'd want to remove that rust. Hmmm. Wonder what the internet knows about rust removal. And straightaway I found two fascinating sites. One, there is store devoted to only this: . Gotta love it. And two, wikihow has like eight ways to do it: .

  3. Hi David

    Yes, there are at least two kits for updating the power supply, which replace the huge 1960s era electrolytics with modern versions that are just over 1" in diameter and about an inch high.

    I have begun to remove the rust like coating - using mild cleaners at first (409 for example), I got quite a bit off and did not find raw metal underneath. It is some kind of dust that was heat baked on the power supply.

  4. The particular kit I used was sold by K8GNZ