W8CDX 1930s FD Setup at NO3M


I had been tossing around the idea of doing an antique FD (Field Day) setup this year after having a lot of fun running my 1920s replica transmitters during several of the recent 160M Stew Perry (TBDC) events.  Once I committed to the idea by inviting several friends out for Saturday afternoon, I knew it was time to get busy, as I did not even have a transmitter built for 40M yet and it was about a week and a half before the FD weekend! Continue reading W8CDX 1930s FD Setup at NO3M

Electrolytic Rectifiers

Before tube rectifiers were readily available, electrolytic rectifier banks (Slop Jar rectifiers) were common.


There is numerous literature in old QSTs on the construction, use and care of these type of rectifiers:

“A Symposium on Aluminum Electrolytic Rectifier Operation”, June 1922 QST

“Operating Notes on Electrolytic Rectifiers”, Sept 1921 QST

“An Electrolytic Rectifier for C.W.”, Feb 1921 QST

I chose to use a solution of distilled water and Sodium Bi-carbonate (Baking Soda), which works just as well as the more popularly referenced Sodium Borate (Borax).  A 385-0-385 volt Thordarson power transformer was used during initial testing, each side of the high voltage winding connects to a bank of eight (8) jars, C.T. (center tap) “grounded”.  No smoothing filter has been setup yet, but the output of the rectifier bank shows 400VDC on the voltmeter.  Once a suitable permanent setup is built for the transformer and filtering components (Stancor swinging choke and 20uF oil capacitors), this rectifier will be part of a B+ supply for several of my 1920s reproduction rigs.