The “Old Buzzard” AM Rig at NE1S
First, so that there is no misunderstanding, allow me to explain the term “old buzzard.” To do this, I'll quote from W1UJR's excellent web pages: “Far from being a derogatory term, the name 'Old Buzzard' is most kindly thought of in the amateur radio community. Being an 'Old Buzzard' has much more to do with a state of mind than chronological age, but often Old Buzzards are indeed the elder members of the amateur service fraternity.” For a more in-depth analysis please refer to http://www.w1ujr.net/old_buzzard.htm. I call this transmitter the “Old Buzzard Rig” because it represents the type of rig a contemporary Old Buzzard may have built and operated as a much younger ham.
This project began when I visited Linwood Cook (“Cookie”), W1JRS, (now SK) back in the mid-1980's shortly after obtaining my ham ticket. He had this beautiful 1930's open relay-rack with several black-wrinkle panels, and some decks, installed. I expressed my admiration, and some time later he offered it to me. After moving it to my place and inspecting what I had, I found that this was not a complete transmitter, but certainly it was a good foundation for a fine example of a latter 1930s homebrew amateur transmitter. (Cookie had told me the guy who originally built it was the chief engineer at WGAN in Portland, Maine, at the time, where Cookie also worked. I wish I knew is name and/or callsign, and wish I had recorded this info from Cookie when he was still with us! I just got a lead (1/7/08) that Warren Hamilton, W1KNB, might have been the original builder.) This is what was installed in the rack originally, top to bottom:
1. metering deck
2. final amplifier deck, incomplete (no input tank, two 4-pin sockets but only one of them was wired)
3. exciter/frequency multiplier deck using 6A6 triode sections as xtal osc., doublers, and an 807 IPA – beautifully constructed! It supplies about 30-40W on 80M, 40M, 20M, and 10M through bandswitched link-coupled coils.
4. power supply for exciter deck using 83 mercury-vapor rectifier
5. regulated bias supply (not using this, ran out of rack space!)
6. three blank panels
I was able to obtain similar-vintage high voltage (1500V) power supply and speech amplifier decks from another old gentleman ham in Portland. These were also of black-wrinkle 19” rack panel & chassis construction. The power supply uses a pair of 866A mercury-vapor rectifiers (what else?) and the speech amp was wired for 6A3s as the audio drivers. Since I didn't have any 6A3s I replaced the sockets with octals and rewired them for 6B4s, which I was fortunate enough to have in my tube stash. Electrically they're the same.
At this point I got involved in other projects (such as building other stuff you've seen on my homepage, as well as lots that’s not posted here), not to mention raising a family and working for a living! But by 2005, about 20 years later, I had gotten down the list of projects enough to be able to resume work on this transmitter. I built up a plate modulator deck from scratch using 805 triodes on a NOS steel chassis I had stashed away, and painted it black wrinkle after all the drilling and punching was complete. I used one of the blank panels that came with the original unit for the modulator deck. A BC-610D modulation transformer I purchased from Fair Radio many years ago was pressed into service. I also built a bias supply and a keep-alive supply for the high-level negative peak limiting circuit on the modulator chassis. I used 3 high-voltage diode modules in the – peak limiting circuit, not period-authentic, but since it's also protection for the modulation transformer it's a worthwhile compromise. I did use tube rectifiers in the supplies (an 84 for the keep-alive supply and a pair of 1-Vs in the bias supply). The filament xformer in the modulator deck has two 10V windings: one supplies filament voltage to the 805 modulators, and the other winding lights the RF finals through a suitable dropping resistor in each supply lead.
Modulator deck top view:
Modulator deck bottom view:
The final deck looked like it was being built to use push-pull triodes, so I finished off the final deck to employ a pair of 812s I had on hand. I plan on converting it to T-55s which I have since procured. I added a split-stator variable capacitor below the chassis, as well as a five-pin socket to accept link-coupled plug-in coils for the grid tank circuit. I also added a plug-in 50pF fixed vacuum capacitor from plate-to-plate to supplement the rather small plate tank split-stator air variable above the chassis on 80-75M. It is not used and removed on 40M and above. The single plate tank coil that came with the deck was for 80M, and since this was to be a multi-band rig, the coil was in kind-of rough shape, and the jackbar was non-standard, I replaced the jackbar with one that would accept some BC-610 coils I had collected with this project in mind.
Final deck, as received, top view:
Final deck, as received, bottom view:
Final deck, completed and installed in xmtr, top view:
I wired all the decks together with vintage cloth-covered wire from a harness scrapped out of an old broadcast xmtr. I never laid eyes on that transmitter, but “dumpster-dived” for the harness! The transmitter first saw the airwaves in February 2006 for the final few hours of the AWA AM QSO Party, running on 75M. The intent was to complete it in time for that event, but I was running behind! Over the course of the next year I worked out some bugs, optimized a few things, and repaired some failures – I lost the 1st choke in the HV supply and the exciter plate transformer, and had to replace with suitable substitutes from my well-stocked junkbox. The transmitter has been used on 20M, 40M, and 75M, but spends most of the time tuned up on 75M. I run it at about 275 – 300W RF carrier output. Still need to get things tweaked in for 10M operation – I require a tad more drive to the 812 grids on this band. Here's a an air check recording made and sent to me by my friend Bill, KC2IFR, of Glens Falls, NY, in autumn 2007. Mine is the voice making the long (“Old Buzzard!”) transmission towards the end of the file describing the rig, and promising to put some photos up on the web. I guess I've fulfilled that promise.
Complete Old Buzzard Rig, from the rear:
As you can see from the pictures I have installed a 1935 HRO receiver in the middle of the rack. This is why the original bias supply had to go. So this rig is truly a 1930's complete “shack-in-a-rack!”
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