I spent most of July 2017 visiting with my sister Barbara, who is on a US Peace Corps stint in Albania, a rare DX entity. Besides seeing her again after a 15 month absence, I had in mind scouting the country for a holiday style DXpedition. Once there I discovered it has spectacular mountain ranges that would make for great SOTA activations. Here is a short slide show of some of the highlights of the trip.
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4/3/17: Just completed chassis layout V1.1. Found an even better GBU805 diode bridge in a salvaged washing machine DC motor controller along with two cherry 680-mF electrolytics. This diode features 600 PIV (had no specs for the previous diode) so I also added a 6H choke. The block is bedded to the chassis side, using it as a heat sink. Calculated resonance came out to ~2.5Hz based on formula f=1/2PI * sqrt (LxC). Adding the choke knocked down the ripple from ~ 350 mV to a few microV with the 30K ohm load resistor. The best I could get with the half-wave diode was between 3 and 5 volts of ripple. I was concerned about flyback voltage hurting the electrolytic cap on power down but neither the DMM nor the ‘scope showed any spike. The cap is rated at 200 VDC and the load voltage measured at 142 VDC.
I have a bunch of dual diode tubes including 6 and 12 volt types so I’m working out which to use for phase inverter and which for PP power stage. Also added 3A fuse to AC mains and 1A fuse to AC secondary winding, then re-arranged power supply parts to one end of the chassis for isolation. Preamp and PA tubes will be at the opposite end.
3/13/17: Decided to do a build-along while we’re on the audio amp analysis, using junk-box tubes and parts. In the slide show above, the tube right in front of the transformer is a 6SN7GTB dual triode from a HP 200AB sine generator I got at a hamfest. That gives me the phase splitter/preamp. Undecided on PP tube but have a few octals that could work. My 6J6 reads weak on the B&K tester. Next to it is a 5Y3GT I might use for B+. The repainted junk box transformer puts out 105 VAC nominal and 6.3 for filaments. Underside shows half-wave rectifier pack from an appliance tear-down. I’ll try to filter out the bumps and use either the 5Y3GTB or the 35Z5 that came with the Philco AC/DC radio if I can’t. Maybe. Have to see if I can get away with only 100VDC B+; theoretically should be possible but I’ll have to redo the component values.
I’ll look for a few 12AX7s and 6360s at the Maine State Hamfest this weekend just in case. FWIW I am amazed that some on-line vendors want over $100 apiece for so-called “gold-pin” tubes for each type, as if I’d be foolish enough to cough up that kind of cash for run-of-the mill tubes.
I’m always amazed how much time it takes to chase down parts and build stuff. My hat’s off to Paul for not only putting together the projects but also shooting and editing the videos. That’s all very time consuming.
I intend this as a ghetto-class, bread-board effort, simply a test fixture to learn on using expendable parts if I goof up. I’ll be saving the higher voltages and high-power tubes for follow-on projects. BTW, the line cord is not fused b/c I’m connecting to mains current via a fused VARIAC. I hope we get to reading tube data sheets and how to plan a design. Where to put the stake in the ground and start is always the hard thing for me.
4/3/17 UPDATE: Just completed chassis layout V1.1. Found a diode block in a salvaged washing machine DC motor controller along with two cherry 680-mF electrolytics. The diode features 600PIV so I also added a 6H choke. Calculated resonance came out to ~6Hz. Adding the choke knocked down the ripple from ~ 350mV to a few microV with the 30K ohm load resistor. I was concerned about flyback voltage hurting the electrolytic cap on power down but neither the DMM nor the ‘scope showed any spike. The cap is rated at 200 VDC and the load voltage measured at 142 VDC.
Guide rails center and hold ladder in place.
Check out this latest project: Tower Safety Stand Project
Now that summer fun is over its time to get back to some serious antenna work. I decided that along with an inverted L for top band, I need a decent receiving antenna(s) to dig weak signals out of the noise on the low bands. The K9AY terminated loop looks like a good antenna to start with so I’m building that. Rather than blindly copying a known design I decided to use some new test gear I got last year to do some bench comparisons on cores I had on the bench. Very instructive, to say the least. More info here: Toroid Testing
In January of 2015 I decided to splurge a bit and order a K3-100 radio kit, with the 8-pole 400Hz and 250Hz CW filters. I’ll probably add the sub-receiver and maybe even the pan-adapter later on. This slide show documents my progress so far. Click your mouse on the icons on the slide to stop or reverse the show.
First I framed the top and bottom of the hole to attach form sides, to keep dirt from falling in the hole – the dirt is really the form here. Bottom frame ID 47″ x 35″, top frame 40″x30″ to give pyramid shape to eliminate frost heave. Next I set and leveled the rebar, then bolstered the forms to make ready for the pour.
I calculated two yards of concrete to fill the forms with a little extra, so I made up a form to use any excess for guy wire sleepers. No guys for this tower but who knows what the future may bring?
I followed the Hygain tower recommendations for the rebar but made the block larger (two yards concrete vs 1 yard) for a safety margin. The block sits on ledge rock and should be very secure.
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Got the backhoe in to dig a hole for the tower base block. I’m going with a larger base block than recommended due to the soil conditions, winter frost heave considerations, and occasional high wind conditions here. My QTH is on a ridge just a few miles inland from the Penobscot Bay and the open Atlantic Ocean. Good for propagation to the East and South but subject to high winds from maritime polar air mass lows which often deepen more than forecast. Check out the rocks he had to extract. Not a project for hand shoveling!
Starting the concrete forms work. and a look at what I bought.