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Technical Tips from Mark W. Persons
Checklist for Collins 831/Continental 816 FM 20-25 KW Transmitters

Replace #387 lamps in filament, reset, and plate switches.  If switches break, Continental may not have a replacement available.  If so, substitute switches can be installed.

Mechanically zero the panel meters.

Clean Driver/PA blower blades by running screwdriver along blades to loosen dirt that builds up in them.

Clean overload relay contacts.

Replace capacitors on the three power gating cards and power control card.

Fan over power supply should pull air in.  Reverse fan wiring and fan blade if necessary.  This is a change that Continental made years ago.

Check muffin fan on back of card cage at rear of transmitter to make sure it is running

Move PA bias control and install extender shaft to front of transmitter so the control can be adjusted while the transmitter is running.

Lightly oil door interlocks and check low voltage interlock switches on them.

Add extra IPA door latches in center of door to make it the same as newest transmitters. 

Change rear door bottom screws to tapered type if traditional hex-head bolts are in place.  Continental part number 348-1004-010 for the screw and 786-0910-001 for the Delrin washer that goes with it.  This makes the back doors easier to put on. 

If the transmitter has 4CX250B driver tubes, install a shorted quarter-wave stub trap at the output of the exciter or input to the IPA.  This will prevent high voltages from a tube arc-over from damaging the exciter output stage.

Replace original nylon screws on PA fiberglass air chimney with thumb-screw type.  Continental part number 330-7031-020.  About $1.00 each.

Put the exciter into a dummy load and check for spurious radiation using a spectrum analyzer.  Replace capacitors on exciter RF output amplifier if spurs are found.

Check and adjust the Driver/PA air pressure switch so that it closes at 2� of Driver door opening.

Turn off the exciter and set the modulator bias controls so each tube has 120 m.a. of current for each tube.  Turn exciter back on.  It will be 170 to 190 m.a. when the transmitter is tuned and running properly.

Install a thermometer on the air input filter above the power supply and one above the air output above the PA. 


Tuning:  The Continental instruction manual gives good instructions.  Here are my tips: Adjust the motor-driven PA Tuning control for a maximum (peak) on the PA Screen Grid Current meter.  Adjust the motor-driven PA Loading for maximum (perk) RF output.  If either control cannot reach a maximum peak without running out of range, then adjust the height of the shelf above the tube to get it into range.  Be sure to tighten the shelf hose clamp...or it will arc and create a burn on the chimney.

Adjust the IPA tuning for minimum  reflected IPA power.  Adjust the motor-driven Power Adjust for the desired power level.  Refer to the book to make sure the PA Volts and PA Ampere current aren't too far off factory test data.  

Do NOT use the power output meter as gospel.  PA Volts x PA current x rated PA efficiency gives transmitter power output.  Adjust the Forward Power meter calibrate control on one of the control cards to get it to read 100% when all else is right.

January 18, 2012 e-mail:  Hi Mark, I really enjoyed reading your handy dandy "hints and kinks" for MW and FM.  One other tip I'd like to toss in regarding the FM Continental 816 series, be sure to check the fan on the harmonic filter. Since it is "out of sight and out of mind" it's frequently overlooked.  Another handy mod for combined Continentals using the 377D switcher panel and the Continental combiner.  Install a separate 24 volt UPS protected supply to power the 377D.  This prevents the 377D from losing it's mind during a power bump and cause the coaxial switches to halt mid cycle. Yes I know the 377D has batteries but the amount of down time I've saved with the 28v UPS protected supply is worth the mod.  Thanks again!!!  Jay from Dallas, Texas.

Hopefully this personal list will help others in maintaining Collins/Continental 20-25 KW FM transmitters.

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 

Mark W. Persons   Ham W�MH

Questions?  Email Mark Persons:  teki@mwpersons.com         

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page last edited 06/06/2017