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6m Larcan Conversion

Discussion in 'Amplifiers' started by avistar23, Feb 10, 2012.

  1. avistar23

    avistar23 Active Member

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    Just bought a Larcan through someone i met from Captain Kilowatt.

    I will document the conversion and build process.

    I have a question for amp builders

    the larcan has no provision to turn off biasing, it has a slow turn on sequence if it is hot swapped, and there is no "on/off" pin like some other broadcast amplifiers, the bias is controlled by the swr/ bias board.



    Now.. here come my question, when in receive should i have the whole board cud off with an fet or relay, or should i leave power to the bias/swr monitor board and intercept the outgoing bias with an fet or relay

    this i would have done by a sequencer with the following sequence

    >engage tr relays > engage bias >engage ptt on radio

    is the sequence correct?

    the setup as of now is an ft846 barefoot to a 5 ele 50 mhz yagi

    next on order is an m2 7 ele long boom yagi to replace that.

    my second question is and i know this isnt the place for it

    we have next to zero local activity here (70cm 2m) anything like that

    if i put up a long boom 12 element yagi on 2, about 40 feet, with a good line of sight north into the states, anyone think id hit Miami? or is this a waste of time money and tower space.

    i normally work stirctly HF DX, but i got bitten by the 6m bug a few years ago.
     
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  2. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Glad to see you made contact with Warren about the amp modules. I am on my way over to his place in a few minutes to pick mine up. (y) I'll try and get some info from him.
     
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  3. avistar23

    avistar23 Active Member

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    #3
    Last edited: Feb 11, 2012
  4. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Hi again Michael. I just got back home from Warren's place with my module.I'll have some pictures later tomorrow. Warren suggested switching the bias off during RX standby simply because the module will be dissipating 200 watts of heat all the time and that will get quite hot. The easiest way is to simply break the bias line going from the board to the modules themselves. I can ID that better in a picture and will do so later tomorrow. The easiest way to do it is with a relay tied into the T/R relay. These amps BTW are rated at 1000 watts 24/7/365 and are from a TV channel 3 transmitter that was in operation for no more than 5 years at most. Warren checked the date codes on the FET's and they were dated 2006 so that's not bad at all.

    When I arrived Warren was getting your unit prepared for shipping to your requested destination and it should arrive when it is supposed too. Hopefully there are no problems getting it from there to you. I was surprised at how heavy the unit is. All the units look new but you should take a good look at the circuit board side when you get it. It looks like someone defaced it with graffiti. :whistle:

    I won't be getting mine on the air until summer due to antenna/tower issues and other things but hopefully we can work each other some day using these things on the air. if there is any type of opening from VE1 to C6 land I would think a six element to a 5 or 7 element with a KW+ on each end would be almost unimaginable for signal strength.

    73
     
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  5. avistar23

    avistar23 Active Member

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    Sound great, i agree, that was my whole point for heat dissipation, i just put another section on my rohn 25 tonight, and changed out my coax feeding my HF beam, now i have an intermittent extremely high swr, i think its in the rg213 jumper i used to go to the beam, as lmr400 was too stiff. My biggest headache is chasing swr issues, i hate it.

    it will be well into summer before i get online with the amp also. Looking forward to it. I will check out the board for the graffiti :) Once im online you can count on me being quite active, the beam will be fixed just about north, beaming right up into Canada. I spent 5 years over there in school.

    i am also interested in going QRO on HF, i would like to share the 50amp ps with an FET based HF amp also.
     
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  6. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Ok pictures as promised. The first picture is an overall view of the entire module showing the stripline circuitry and components.There are four FETs which have a Larcan number on them but may be replaced with a standard MRF151G if necessary. This is directly from a Larcan engineer but only after he closed the office door and replied with a whisper. :laugh: The only difference is that the Larcan marked devices have a tighter gain bandwidth for use in television transmission but for amateur use it would never be noticed in a million years. There are four devices and eight fuses. This is because each device consists of two identical FETs in a common package and each FET in that package needs it's own bias adjustment for proper operation. The fuses are removed and only the one connected to the device having the bias set is installed during setup.


    [​IMG]


    Next we see the bias line that needs to be broken on RX. it is indicated by the white arrow. The wide silver bar just above it is the B+ supply rail.




    [​IMG]



    Bias supply buss seen underneath the B+ rail.

    [​IMG]


    Rear view of the unit. The input is on the left and the output is on the far right. Warren has supplied the quick-connect input adapter but has no output adapters. The O/P connector will have to be either replaced or something made up to adapt to a regular connector. I may try my hand at a little plumbing work and try to devise something to adapt to a UHF connector. The DC power connector is in the middle as is the bias board. The bias board gets it's power directly from the 48-50 volt B+ supply.




    [​IMG]



    Close up of the output connector.

    [​IMG]


    Front view of the module. These units normally stand vertically in the transmitter.

    [​IMG]



    Top view of the heatsink. The ruler is a regular 12 inch ruler shown for scale.


    [​IMG]

    Now I need to pick up a cheap 48-50 volt power supply that will deliver at least 45 amps and preferably 60 amps for lots of headroom. With 10-15 watts or so of drive this amp should provide well over 1000 watts of clean class AB1 power on 6m. (y)
     
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  7. vo1ks

    vo1ks Active Member

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    Nice pics Garth...

    I have some gain response curves that may be of interest as well. I'll dig out my notes from Larcan to see if there is anything of use regarding the PA modules.

    Michael, your amp is in the mail...
     
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  8. avistar23

    avistar23 Active Member

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    Thanks for all the updates and pictures, i doubled confirmed that other uses of the larcan have broken the bias this way also.

    Thanks Warren i saw your email a while ago,

    also thos HP PS's that people are using for the harriss amps its under 30 bucks on ebay, quite a steal,

    for the input and output i will most likely completely get rid of the connectors, i will LMR400 from the output right into my coax relay, and a similar fashion with the input, what ive been thinking about the most is that the swr board appears to monitor both forward and reflected power, i would like to scale that to a set of meters, along with a meter for bias correct, and lED for bias voltage, a shunt and meter for +50V rail current, and an LED for voltage.

    id also like to set it up for LED's to show when the relays are engaged.

    its important to me to be able to monitor a wide array of functions and warning right from the front of the case. It will be a long road for my amplifier to be finished, but i plan to use it for many decades.

    Quick question, Does the bias have any form of thermal tracking? or is that not necessary on these FET's
     
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    Last edited: Feb 11, 2012
  9. vo1ks

    vo1ks Active Member

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    I've uploaded files to my web page.
    1kW module frequency response
    PA module testing
    FET testing

    6M / 2M kilowatt amplifiers

    Best approach to the connectors that I've seen is to put a BNC at the input and a Type-N at the output. You really shouldn't hard wire directly to the board.

    I don't recall any thermal protection on the modules. The overall transmitter had air flow and thermal monitoring but not on the individual amplifiers. It's unlikely there is thermal tracking of the bias current.
     
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  10. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Welcome to the forum Warren. (y) I see you found it despite my forgetting to send you a link. :cry:

    For those that do not already know,Warren VO1KS, is the television engineer I spoke about that has the Larcan amplifier modules for sale.

    What do you think Warren, it shouldn't be too hard to cobble up an adapter for that O/P connector using run of the mill plumbing parts and a little ingenuity rather than rip it out and replace it hey? I have made up a few adapters for CATV hardline before and the idea is basically the same. Then again that was for HF while 50 MHz is a little different or at least a bit pickier.

    I guess I need to read all the posts before I make my own post.:blink: I just saw warren's comment about installing an N connector on the O/P. :headbang I will likely go that route but you never know. :whistle:
     
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  11. vo1ks

    vo1ks Active Member

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    The original connector uses sliding contacts. I don't know of an equivalent anywhere. For this purpose it may be easier just to swap it out with a common connector rather than lashing something together.

    In the pdf with instructions to modify for 2 meters, the output connector has been changed to Type-N. I haven't done the work yet, but it seems to be fairly straight forward. A good quality Type-N connector, properly installed is ok to about 3kW at 50MHz, 1.8kW at 146MHz.
     
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  12. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    I have since scoured my junk box, well one of many actually, and found a really good silver plated Amphenol type N chassis connector that I will likely use. The coaxial relays I plan to use also have type N connectors on them and I have a bunch of silver/Teflon Amphenol connectors for coaxial cable as well so it looks like type N all the way to the antenna. The transmission line will be LDF4-50 with type N connectors except for pigtails on either end that will be RG-8 type likely Belden 8214 as I have a couple hundred feet of it just waiting to be put to use.
     
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  13. avistar23

    avistar23 Active Member

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    If you search, someone documented how to use a half inch coppr fitting and a few other things for an adapter, but its rather pointless as its alot more loss and things to go wrong when you can just swap it out
     
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  14. vo1ks

    vo1ks Active Member

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  15. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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