Somewhar in my files, I have a simular circuit...If u like, I'll rummage through and see what I can find..... I think it utilized a 100th as the variable resistor.... klc
----- Original Message ----- From: Don Merz <[EMAIL PROTECTED]> Date: Wednesday, August 2, 2006 5:30 pm Subject: [AMRadio] DC Load To: [email protected] > A local ham SK built himself a variable DC load which I recently > found in > the N3BM estate stuff. The ham was W3QNI. QNI worked for Western > Electricand was a master builder. He must have died 10 or 15 years > ago. I have one > of his transmitters and it is almost a work of art. This "Variable > DC Load" > is no different. > > So this is an aluminum chassis with 2 transformers, 2 tube sockets > and 2 > meters mounted on it. Controls are simple--one on/off toggle and > one pot > labeled ADJ LOAD--MIN--MAX. There are two binding posts on the > front apron > labeled positive and negative.. The Western Electric meters are > mounted on a > phenolic panel that sticks up above the controls. The left hand > meter is > scaled 0-30 VOLTS DC X100. The right hand meter is 0-300MA. A > label across > the top of the panel says "VARIABLE DC LOAD 2500V 300MA MAX". The > two tube > sockets are empty. They are the large old EFJ ceramic sockets for > twist-lock > tubes like 203, 211, 805, etc. There are no grid and plate cap > connectionsso the sockets must have been intended for single-ended > tubes. The socket > connections are wired in parallel--plate to plate, grid to grid > and fil to > fil. > > One transformer has 150V/50ma and 6.3V 1.5A secondaries. The 6.3V > just runs > the pilot lamp. The 150V is wired, with a silicon diode, > electrolytic cap > and two big ceramic resistors into the circuit with the load > adjustment pot. > The other transformer is unmarked, but it provides filament > voltage to the > tube sockets (in parallel) and the center tap is connected into > the load > adjustment circuit. Filament voltage at the socket terminals > measures 10VAC. > > I went through my files and found a photocopy of a very similar > circuitusing 6BG6 tubes in parallel. But I guess I'm not sure what > tubes this one > was intended to use--likely something that is expensive these > days. I'd like > to put this thing to it's intended use. But I don't want to put > $100 worth > of tubes into it. What are the options? Any ideas appreciated. > > 73, Don Merz, N3RHT > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
