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Sailing Vessel Charisma

1969 28 foot Rhodes Venture

 

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As I found it, it was obvious that it needed some tlc and a lot of elbow grease to turn it back into a reliable unit. The first job was disassembly and cleaning.

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The wall-mounted components components were in pretty-good condition, but I wound up replacing the audio driver-related capacitors and a number of bypasses. The 807 rf driver tube shields originally made by Millen needed refinishing.

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Gates stuck to the 833 triode design long after RCA, CCA, and McMartin were building similar transmitters with 4-400 tetrodes - probably because, after selling so many of a proven design, they saw no reason to change. If I recall, the subsequent model was the same as well, excepting a solid-state crystal oscillator assembly. After that model came the MW-1 - the world's first solid-state 1 kw broadcast transmitter.

The cylindrical "sockets" for the filament connections were badly corroded. I turned them on a lathe while using a rotary wire brush, and re-tapped the setscrew holes.

The two RF 833s on the right turned out to be the only tubes that were usable after the restoration.

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This was the first model to use modern solid-state rectifiers rather than tubes - but those early diodes were fragile compared to today's parts, so they were replaced. All of the high-voltage wire was old and brittle, just begging for disastrous arc-overs, so that was replaced.

One of the first jobs was to install casters on the bottom of the chassis to permit easy movement. Unfortunately, during the transition to vertical, a support line slipped, causing an unforeseen swing which badly gouged the original HV transformer. Fortunately I had another similar unit in my packrat area which I retrofitted without much trouble.

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I made Delrin standoffs for holding the existing wiring harness away from chassis as much as possible to avoid future failures.

I encountered a few odd modifications which had to be undone, and a few failed connections. Unlike the earlier BC1T, this model featured a swing-out hinged chassis for much of the circuitry, but it is much easier to remove the right-side panel for better access.

I installed a new RF driver (807) plate relay which followed the HV contactor - normally the oscillator, buffer and driver come on with filament. I needed it to follow the HV so as not to operate without drive during periods of receive.

The output network was originally a PI-L-C-L with two of the coils being the front-panel rotary variables. Not needing 73+ dB harmonic attenuation, I converted to a PI-L by changing the two capacitors and removing the last LC.

RF amps The 0-5 RF ammeter on the front of the unit was burned out, so I built a torroidial sensor for a period 0-1 milliamp meter using a 22 turns on an FT-140-61 core terminated in 50 ohms, with sample voltage rectified by a Schottky diode. It works quite well and is accurate within about 3% from 1 to 4 MHz, compared to a known thermocouple unit.
W4NEQ I thought a new call placard was in order - complete with lightning bolts ...
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On the suggestion of Don, W4KYV, who converted his BC1T to 160 meters, I modified the oscillator stage by grounding the grid with a capacitor, and driving the cathode through a 1:4 torroidial unun. To ensure stability I ultimately used a 6 dB pad at the VFO input, which accepts 5 volts p-p for normal drive. The 12BY7A buffer stage required removing some turns from the plate tank coil, and replacing the parallel fixed capacitor with a variable to resonate.

I re-did the internal 50 ohm load with a relay - and installed a front-panel switch in a previously drilled "pre-sunrise power" hole.

W4NEQ Part of the transmit / receive switching included receiver mute, antenna transfer, VFO activation, and sequencing to ensure switching without hot RF. There was also a need to convert the classic push-to-talk to independent on/off momentary transmitter activation, without overriding the existing overcurrent protection relays. A cast box kept this shielded.

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Late December, 2012 - the unit is finally operational on 160 meters, remotely controlled from the operating position.