MMRA - Larcan Power Amplifier Information
Google Groups forum:
https://groups.google.com/forum/#!forum/larcan-6m-amplifiers


Purchasing Information

Quantity Left as of 4/20/17: 0
To purchase an amp directly from MMRA, please contact K1IW (at) MMRA (dot) ORG.

MMRA has a limited quantity of lo-hi (ch. 5) 1500W units for purchase.
These are the six transistor units. Conversion instructions below allow these units operate on either the 6m or 2m bands. Please review the instrctions to be sure you are up to it before committing to a purchase,


Amps will require modifications as described below to prepare them for operation
in the 50-54 or 144-148 MHz ham bands. (see documentation below)

These amps are available to licensed amateur radio operators only.

To purchase an amp directly from MMRA, please contact K1IW (at) MMRA (dot) ORG.
DescriptionMMRA Direct Price Includes Shipping
1.5Kw Final Amplifier$375
IPA2 600W Predriver (Same form factor but less transitors)
More Info
$200

Shipping mentioned above is to continental US addresses.
If you want them shipped outside of this region, please contact K1IW for pricing.

Payment Instructions:
If you have any questions, or wish to purchase an amp directly from MMRA, please contact K1IW (at) MMRA (dot) ORG. Be sure to include your amateur callsign and shipping address with your payment!

Send by Paypal to payments (at) mmra (dot) org.

On pay by check: Make checks payable to MMRA and send to MMRA, PO Box 669, Stow, MA 01775.

You may contact K1IW (AT) MMRA (DOT) ORG with any other questions.


Links & Documentation

Schematics
  • VHF-lo 1KW PA schematics
  • VHF-lo 1.5kW PA schematics
  • VHF-hi 1.5kW PA schematics

    Manuals w/Schematics
  • VHF-lo 1kW PA manual w/schematics
  • VHF-lo 1.5kW PA manual w/schematics
  • VHF-hi 1.5kW PA manual w/schematics

    1kW Amp Mods
  • Mods to convert 1kW lo-hi version to a lo-lo (K1IW)
  • Mods to convert 1kW lo-lo or lo-hi to VHF-hi (2m) operation (WA1ZMS)

    1.5kW Amp Mods
  • Mods to convert 1.5kW lo-hi version to a lo-lo (K1IW)
  • Mods to convert 1.5kW lo-lo or lo-hi to VHF-hi (2m) operation (N4NGZ)

    Miscellaneous
  • Improving Larcan 50MHz performance at the low end of the band (K1WHS)
  • A reasonably inexpensive 48V power supply (search for 'hps3kw' on eBay).
      Note that this supply has a minimum current of 5.7A (NOT energy-star certified)! Set bias of the 8 FET's to 750mA each and it will be OK.
  • Replacing the Connectors (K1IW)
  • MRF151G transistor datasheet
  • Real world experiences with pictures by W1BRI
  • IPA1 & IPA2 information
     


    Amplifier Conversion Information

    In all, there are six amplifier types: three frequency ranges and two power levels:
    NameOriginal RangeConversion Information Available
    To 50-52 MHzTo 52-54 MhzTo 144MhzTo 222MHz
    1kW Amps
    lo-lo54-72 MHz (Chs. 2 through 4) INFO Not Necessary INFO NO
    lo-hi76-88 MHz (Chs. 5 and 6) INFO INFO INFO NO
    hi174-216 MHz (Chs. 7 through 13) NO NO possible Not Necessary
    1.5kW Amps
    lo-lo54-72 MHz (Chs. 2 through 4) possible Not Necessary INFO NO
    lo-hi76-88 MHz (Chs. 5 and 6) possible INFO INFO NO
    hi174-216 MHz (Chs. 7 through 13) NO NO possible Not Necessary

    In addition to the final amplifiers, there are two intermediate power amplifier stages - IPA1 and IPA2. These are described here.


    W1BRI photo
     


    Background

    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
     

    More Information

    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).  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 four SRF-3943-2 FET's for 1kW video/SSB or 600W CW/FM. According to Larcan, and confirmed by Freescale Semiconductor who now owns this Motorola business, the '3943 is functionally equivalent to a MRF151G. M/A-COM has the build rights and is currently producing these. This device is rated at up to 175MHz, 300W (150W per FET). The MRF151G is available from rfparts.com for $110 - $120. If you really want the original SRF part marking, you can buy one from Larcan for $200. The datasheet for the MRF151G is in the links section above. Eight 10A fuses protect each half of the four dual-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. 

    Transmitter B+ runs on 50VDC but it will also run just fine on 48 VDC.  Current draw is 35A per PA module at full power so you'll need at least a 45A power supply for 600 Watts. 

    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.



     

  • Thanks to K1RJZ and for the original source of this page.