Construction of a push pull circuit is a real difficult project if started wrong. It has been my experience to find that the plate tank and grid tank do need to be as far apart as possible if plug in coils are to be used and they need to be at right angles to each other. Some folks choose to use a band switched coil arrangement where the grid coils and switch assembly can be in a completely shielded case of its own or below the chassis that is sealed up for RF. I have actually used a Johnson Match Box 500 as a grid drive circuit years ago. It sat on the desk and I used that 300 ohm shielded cable that Radio Shack, sold years ago, to feed it to the grids. I put two RF chokes in the Match Box to attach the grid leak resistor and bias supply to. It worked quit well. I remember I could adjust the length of the twin lead cable to get better results on some of the higher frequency bands.
I prefer the switched coil assembly in a shielded box and mounted under the chassis myself. You may find more ideas at http://wa5bxo.shacknet.nu/wa5bxo.qsl/pptriodes/pptriodes.htm Good Luck John, WA5BXO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of ne1s Sent: Monday, February 06, 2006 2:31 PM To: AM Radio Reflector; [EMAIL PROTECTED] Subject: [AMRadio] Push-pull Triode HF PA layout question Hello all, I humbly request the experience-based advice of this esteemed group. Background: I am working on a project, part of which involves completion of 1930s Push-pull trode PA deck for 80M - 10M. Notice I said "completion," not "construction." This deck already has the plate tank components, tube sockets, and neutralizing capacitors mounted on a beautifull black-wrinkle chassis & panel. The axis bisecting the holes for the tubes is parallel to the front panel, the plate tank air variable (split stator) is perpendicular to the front panel, and the plate tank coil (plug-in jack-bar style - actually I'll be using BC-610 coils, link-coupled to the antenna) is centered directly behind the plate tank capacitor, with its axis parallel to the front panel. What this deck lacks is a grid tank circuit, which I need to add. The tubes will be 812s or T-55s, and will be plate-modulated for 250 - 300W output. Question: What is the worse sin: lack of physical symmetry, or proximity of the gazinta to the gizouta? It seems that I'll have to compromize one or the other in adding the grid tank circuit, based on the present layout. The grid tank will be link-coupled to the exciter. Thanks for your assistance, -Larry/NE1S ______________________________________________________________ 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
