Surplus  1kW  6-meter  PA



                                                                       www.gemoto.com/LarcanPA.htm
Background
Do you wish to burn a hole in the ionosphere on 6-meters?

A well respected Canadian company named Larcan was the first manufacturer of a 100% solid-state, high power VHF television transmitter. These transmitters used hot-swap 1kW PA modules to combine power up to 85kW. The Larcan philosophy was and still is "KISS".  The reliability of Larcan VHF transmitters has been phenomenal. 

Much like the post-WII surplus radio era and later commercial two-way radio surplus era, the potential for a second long lifetime in high-power amateur service is compelling.

                   
click image for more details
 

The two frequency ranges are of interest to 6-meter hams are:

  1. low-split lowband TV ch-2,3,4 (54-77 MHz) :  works on 6M with no mods
  2. high-split lowband TV ch-5 & 6 (77-88 MHz):  Also seems to work quite well as-is on 6M per the tests below.  If you wish to take an extra step, simple jumper and chip cap mods bring it to the full-power, on-freq version.


W1BRI photo

 


W1BRI photo

 


W1BRI photo
 


The Minuteman Repeater Association in the Boston area has received a very limited number of these very high power 6-meter PA's and will be selling them as a fundraiser for ham use only.  MMRA is selling them direct and through Buy-It-Now on eBay


Purchasing via eBay  as of Sunday, January 03, 2010  
(high split $350 with Buy-It-Now)

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330387252314

Or go to eBay and do a search for "Larcan"

50V power supply: Search eBay for "HP 226519-001" or "HPS3KW"

Purchasing Direct
Please send e-mail to K1IW (AT) MMRA (DOT) ORG for questions on ordering information. Please do not send payment without contacting K1IW first.  We need to make sure we have amps in inventory for you as they are selling quickly.

Local pickup is available in Northborough or Waltham, MA. Add $30 to the prices below to have the PA shipped. Payment by personal check, money order, bank check, or Paypal. Add $14 to the prices below if paying by Paypal:


hi-split (simple mods required for full 1KW SSB, 600W CW/FM) $320

lo-split (currently sold-out) $370


PAs ship fed-ex ground after payment clears the bank. For the local pickup option, contact K1IW for more information.


Real world technical and conversion info:

Brief PA schematic    NEW-> Full 20-page PA manual w/schematics

Ham 6M conversion info        Sample 50V PS via ebay

Real world experiences with pictures by W1BRI
 

 

Drill down
Advance to  2010.   The original model 1kW FET PA module debuted in 1987 and is still in production today.  This may become the TV surplus equivalent of a GE MASTR-II !   In a May 8th 2006 test at Larcan's Mississauga, Ontario production line, a 53 MHz carrier was introduced into a low-split lowband VHF transmitter power amplifier module.  To no surprise with ten-watts of drive, this PA made a full 1kW output with video modulation (similar to SSB) and a solid 600-Watts when in CW/FM.  This CW test is essentially the same as comparatively narrowband 5KHz modulation when used for FM voice communications.    

To be conservative, the PA's are rated at a minimum of 20dB gain when on the correct frequency.  However, spec sheets from factory testing of a standalone PA typically yields 22dB gain.

 

5dB per div sweeping 45-100 MHz on a high-split lowband VHF PA (77-88 MHz) under test at 51.050 MHz. Expect a cool 300W+  FM even when used out of the default factory spec. Expect a full 600W FM/CW when using a low-lowband split PA at 51 MHz (54-77 MHz factory spec).  The simple chip cap and jumper mods below will bring a high-split lowband PA into the low-split lowband frequency range at full specs.


W1BRI photo    (more info here)

Many PA's exhibit 22dB gain but 20dB is spec.  When operating out of factory spec with no mods (high-split lowband), expect the overall PA gain to reduce from 20dB to 15dB.   Only a few jumper and chip cap changes are required to convert a high-split lowband PA into low-split lowband at a full 600 Watts FM.  But even with no cap changes 300-Watts is plenty of power for most uses.  You can also get by with a smaller power supply at 300 Watts.

Suggestion:  Don't want to run 600W FM with a power supply good for 50V ~45A?  How about a meager 300 Watts?  Just purchase the high-split version and don't touch a thing.  By default the reduced coupling values will give you less RF power and far less DC current drain.

We were told by Larcan not to expect spurious emissions but obvious good engineering practices will require a look.
 



 

As amazing at it sounds, this is also a 1kW hot-swap PA.  The small 39V bias circuit board on the back ramps-up the biasing for a smooth, surge-free power-up sequence. 

The low current bias regulator also sources the bias voltage to the PA transistors for several other reasons.  It also sets the broadband frequency characteristics for a flat response across several TV channels.  This adjustment with pots located at each transistor, is not typically needed in 5 kHz "narrow-band" amateur service. This 39V regulator works off-of the primary 50 VDC B+ line. 

As with Motorola MSF-5000's and Spectras, you may want to replace the eleven blue electrolytic caps.  Unlike the Motorolas, these don't typically leak but to be safe, it is a suggested Larcan factory update after years of 24x7 operation... strictly optional.

You may want to change-out the special hot-swap RF connector (bottom) and B+ connector (top).  MMRA can sometimes provide the DC power connector mates if asked.  The main RF output area is simply the last rear-edge trace on a PC board so swapping the special RF connector with an N-connector may be easiest

 

The board uses eight SRF-3843-2 FET's per PA module for 1kW video/SSB or 600W CW/FM.  Eight 10A fuses protect each of eight FETs.  The fuse removal will also allow for optimal  biasing of each transistor for multi-channel wideband TV service. That adjustment is rarely required for ham operation due to the 5 KHz maximum modulation bandwidth typically used.

 

 

 

Replacing the SRF-3843-2 power FET is actually quite easy when using
standard practices.  Note the unsoldered tabs when the picture was taken. 

 

Current draw is approximately 38A per PA module at full power so you'll need at least a 45A power supply for 600 Watts FM/CW.  Transmitter B+ runs on 50VDC but it will also run just fine on 48 VDC.  Multiple cooling fans are mandatory.

NOTE:  These tests in no way suggest out-of-band capabilities on behalf of Larcan and this use is not supported by Larcan.  These are deliberate, non-normal tests when used outside of factory approved limits for amateur radio uses.