Winter 2018-19 Boat Anchor Season

As summer wraps up here and turns into fall I start shifting from QRP-In-The-Park to Boat-Anchors-In-The-Basement and the winter contest/operating event season. One station in the works here is a moderate capability mid 30s CW setup using a couple of TZ-20s (at about 50 watts) in the final and a National FBX-A receiver. It qualifies nicely for the AWA Linc Cundall Memorial CW Contest.

I've now finished up the transmitter power supply so I'll soon be testing it out on the air. The transformer is rated for 560V at 270mA so should certainly easily handle my 50-70W transmitter. At 31 pounds, mostly iron, I don't plan to move this one around much.

Next on the to-do list is to go through the FBX-A getting it on the air.

Thanksgiving Day Power Supply

After Thanksgiving Dinner this year I took the opportunity to make progress on the power supply for my 1939 transmitter.

I completed the  500 VDC and 7.5 VAC sections needed for the amplifier.  PSU Designer II indicated that I needed to allow for almost 2000 volts across each of the diodes in the bridge rectifier. I ended up using two 1000 PIV diodes in series for each leg of the bridge. This is a boat anchor power supply with silicon hidden under the chassis. It needed some glow. I added a type 80 rectifier connected only to 5 VAC so that it would look right. After all, real radios need to glow in the dark.

Eventually I'll add components to power the oscillator/buffer stage including 250 VDC, 150 VDC and 2.5 VAC. In the meantime I can drive the amplifier with either my Utah Jr or Meissner Signal Shifter.

More about a power supply for a 1939 Transmitter

Plans change....after studying my collection of available transformers I found one rated at 560 (center tapped) at 270mA. This would work well with a full wave bridge rectifier as the TZ-20 final stage B+ (550VDC). Half of this, full wave center tapped rectified, is about right for the buffer stage (270VDC) and a VR-150 should be able to take this down to 150V for the oscillator stage.

I recalled Brian, WA7PAC's, comment to me several years ago when I was
dealing with a similar problem on a different transmitter. He suggested an "Economy Power Supply". Rather than clone my one transformer it's possible to run it with both a full wave bridge rectifier and a full wave center tapped rectifier.This looks like it may work.

I'm using PSU Designer II to help me play with filter options before I put solder to the iron.

A power supply for a 1939 Transmitter

With my KX3 n the shop because of a bad output transistor and cool weather returning to SE Minnesota I'm again in the basement looking at boat anchor projects. One project on my list is to clean up the power supply for my 1939 transmitter. Right now I've borrowed the power supply from my 1951 novice station to power the oscillator/buffer stages and used a second 500VDC supply for the TZ-20 amplifier stage. Needless to say, these don't show up in my blog photos of the transmitter.

My new power supply is a pretty brute force design delivering 550VDC, 300VDC and 150VDV to the transmitter using two power transformers, a couple of 5R4 rectifiers, a VR-150 and the needed filtering circuits. It will be two fairly heavy supplies on one chassis.

I found all of the transformers and components in my junque box but not a stout enough chassis for all of the iron. I turned to my slat board design to take care of this shortage.