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6m Larcan Conversion

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  #1  
Old 02-10-2012, 11:13 AM
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Default 6m Larcan Conversion


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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Old 02-10-2012, 01:34 PM
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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. I'll try and get some info from him.
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Old 02-10-2012, 04:25 PM
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correction radio is FT-847

and here is a pic of the bias board



Uploaded with ImageShack.us

http://img88.imageshack.us/img88/2600/larcanbias.jpg

Last edited by avistar23; 02-10-2012 at 06:02 PM. Reason: adding bias board pic

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Old 02-10-2012, 06:20 PM
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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.

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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Old 02-10-2012, 07:19 PM
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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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Old 02-11-2012, 11:42 AM
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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. 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.





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.








Bias supply buss seen underneath the B+ rail.




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.








Close up of the output connector.




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





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




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.
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Old 02-11-2012, 12:25 PM
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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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Old 02-11-2012, 12:34 PM
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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

Last edited by avistar23; 02-11-2012 at 12:44 PM. Reason: Thermal tracking

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