This from a collector and restorer of antique electronic equipment, especially pre-1950 radio sets. The 'curtain burner' moniker came [I think] from the fact that radios of the period were commonly located near a window for ease of bringing the antenna connection in from outdoors and the cord got hot enough to eventually leave a scorch mark where it was trapped in the folds of the heavy curtains. Around 1930-31 the tube designers were at a point where they were updating the line of 'high performance' 2.5V indirectly heated tubes when the idea of automobile radios also came to the fore. At that point they decided to 'standardize' filament voltage at 6.3V [the nominal float voltage of a 6V auto battery] rather than the 5V they had intended, and that required 300mA to develop the required cathode temperature. To keep costs down [it was now in the depression] a significant saving could be made by eliminating the power transformer, so 2 new tubes were needed to operate on a 300mA series string filament supply directly off the AC lines. The 43 was the 25V filament AF power output and the 25Y5 rectifier/doubler [soon supplanted with the higher current 25Z5]. These rectifier were usually connected with both sections in parallel as half wave rectifiers so the radio could be operated on DC mains as well as AC. With the advent of the octal base in 1935-36, an equally performing set of tubes was produced as the 150mA series 12SA7, 12SK7, 12SQ7, 50L6 and 35Z5 rectifier. The tube designers [RCA] dropped the ball shortly after WWII when they were transferring the AA5 series of 150mA tubes from octal to miniature in that they misaligned the pinout on the 50B5 such that there was insufficient clearance on the socket to meet UL rules. Within about 2 years they had brought out the 'corrected' 50C5 and after that the 50B5 became quite expensive, but not quite enough to justify tech time to rewire the socket.
We had a box of 'new' resistance cords come into the museum and they were petrified when still in the box. We guessed the mfg. date as around WWII. _______________________________________________________________________________ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
