|
|
|
Input attenuator provides a passive 50 ohm load for the exciter and is rated at 100W. No frequency compensation is needed for 160m and 80m. |
Detail of plate choke construction. The form is made of fiberglass tubing with solid drilled and tapped end caps. |
Completed plate choke has 230 uH inductance. Phosphor bronze hardware is used in strong RF fields to avoid heating. |
| |
|
|
|
|
|
Detail of parasitic suppressors, plate choke, and blocking plate capacitors. Teflon sleeves route the hot exhaust air to vented openings in the top enclosure cover. |
Detail of the RF sensor PCB mounted on the input RF BNC connector, and the two back-to-back Jennings RJ1A vacuum T/R relays. Feedthrough capacitors bypass all the DC leads into the tube compartment. |
This inductor, shown here disassembled, started life as the tank coil in a Gates AM broadcast transmitter |
| |
|
|
 |
 |
 |
| Here is the completed tank coil, all spiffed up and cut to the target inductance of 16.5 uH. Not shown is a tap for the 80m inductance. |
The high voltage cable between the RF deck and the HV power supply uses RG6 coax with reverse polarity "SHV" BNC connectors. This is a safe, rugged way to route high voltage. |
You may not recognize this interior view of a Bird 1000W wattmeter slug. This slug was modified to give a 3000W full scale reading on a 50 uA panel meter. |
| |
|
|
 |
 |
|
| This is the "L2" coil for the tank circuit, fabricated from 3 T-200-2 toroid cores, taped with fiberglass and wound with Teflon-insulated 10 AWG wire. The 80m tap has not yet been installed. |
Detail showing the plate tune and load capacitor mounting. Shaft couplers route the rotors through the sub-panel to Jackson Bros. planetary reducers that provide vernier tuning.The two doorknob loading caps overheated during testing and were changed in the final design. |
These solid state timing modules are an easy, inexpensive way to ensure an accurate warmup time for ceramic-metal transmitting tubes. These are widely available on eBay for about $10. The GU74B requires 180 second warmup. |
| |
|
|
 |
 |
 |
| Look closely and guess who dropped and broke the $150 vacuum relay on the right. Ouch! There are five vacuum relays in the amplifier RF deck, plus another three in the power supply. |
Here's a tidy way to eliminate the frayed ends of coax cable shields. That, plus Teflon-insulated hookup wire, stainless steel hardware, and the liberal use of Ty-Wraps, make for clean wiring. If it doesn't look good, it isn't good! |
There's a lot of paperwork involved in any large homebrew project. Down the road, you'll thank yourself if you make the effort to keep well-organized detailed notes and records on your work. |
| |
|
|
 |
 |
 |
| Breadboard mockup of the screen voltage regulator. During testing, I found a mysterious motorboating problem that took days to diagnose and fix. |
Breadboard mockup of the control grid regulator circuit. |
The switching properties of numerous vacuum relays were evaluated before settling on the Jennings RJ1A for the QSK T/R relays. A digital oscilloscope made comparisons easy. |
