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Author Topic: IC-718 200 watts out  (Read 8233 times)
KB7QND
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Posts: 43




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« on: March 29, 2011, 08:34:17 PM »

I've read about several modifications posted online about an easy adjustment that allows the Icom 718 to increase from 100 watts to 200 watts out.

Has anyone tried this modification and if so, what were your results?
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KC7YRA
Member

Posts: 254




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« Reply #1 on: March 29, 2011, 08:44:28 PM »

While I myself have not done this mod, I know several who have and have experienced rapid final failure. 

The output finals are not rated for that kind of power.

Plus, going from 100 to 200 watts is a 3db gain.  About 1/2 of an "S" unit.

So save your finals since you aren't gaining much.

Brad
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NO2A
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Posts: 678




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« Reply #2 on: March 29, 2011, 09:18:58 PM »

Besides ruining your finals this would also be illegal,cause it would splatter your signal up and down the bands. This is why the power level was set to 100 watts at the factory,to give you headroom(margin for error). You wouldn`t drive your car at maximum r.p.m.`s until the engine seizes up. It`s the same thing with your radio.
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W8JX
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Posts: 5004




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« Reply #3 on: March 29, 2011, 10:40:29 PM »

I ran a Kenwwod TS-140 at nearly 200 watts out in a mobile for many years in 90's without failure. I did add a aux cooling fan to it. I theory a pair of 2sc2879 can handle this okay "if" they are properly cooled. The 500 watt Ameritron mobile amp uses 4ea 2sc2879's in it last time i checked.
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KA1MDA
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Posts: 543




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« Reply #4 on: March 31, 2011, 03:28:35 AM »

You won't get 200W out no matter what mod you do. What you will get is maybe 110W out with enough clipping and wide band distortion products to fool your watt meter into reading higher.

To get an honest 200W out would require almost doubling the DC input power- that means 40A or so from your power supply. The original power cable and fuse holders are barely adequate enough to provide the 20A or so the radio needs to produce 100W.

Think of it this way- if there was a quick and easy way to double the output power, don't you think the radio manufacturer would have incorporated it in order to increase sales thru bragging rights? Or perhaps offer a 200W model of the same radio for a higher price?

Please do yourself (and everyone else on the bands) a favor and don't monkey with the settings. Unless you have access to a wide variety of expensive test equipment, including a spectrum analyzer, you have no reason to be poking around in the service menu. There is far more involved here that looking at a watt meter...

Tom, KA1MDA
www.ka1mda.org
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W8JX
Member

Posts: 5004




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« Reply #5 on: March 31, 2011, 04:52:35 AM »

I change fuses on mine and a 25 or 30 amp fuse does not blow at 25 or 30 amps. Radio are made conservative for reliability and pushing it to 200 watts can compromise reliability and create cooling issues. Unless you know what you are doing and have your ducks in a row so to speak you should not push design output power. Yes it can be done but it is not a simple plug and play because stock cooling will likely not handle it. 
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N4NYY
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Posts: 4742




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« Reply #6 on: March 31, 2011, 06:00:29 AM »

3 words. Buy an amplifier.
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WB6BYU
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Posts: 12773




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« Reply #7 on: March 31, 2011, 09:02:56 AM »

There is a lot of confusion on transistor ratings.  While it may be possible to get more output
power from a given set of transistors, the distortion level often rises rapidly, and the mounting
must be designed to dissipate more heat.  The former may make you unpopular with other
hams on the band, and the latter may fry your finals.  The transistors also are running
closer to their maximum voltage and current, so are less tolerant to SWR.

Transistors are generally run at less than the maximum output power for these reasons.
It is good engineering practice.

I remember there was a mod to run the TS-50 at 200 watts output.  Someone tried it and
reported that it dropped his usable bandwidth on 20m to 10kHz because the SWR shutdown
circuitry was so sensitive at the higher output power level.


Go ahead and make the mod if measured output power into a dummy load is more important
to you than having a clean signal and having a reliable rig that will last for many years.
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KB7QND
Member

Posts: 43




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« Reply #8 on: March 31, 2011, 06:29:04 PM »

I happened to see the mod when I was looking for the mod information for extended transmit for MARS.

I was curious about it.  I'm not going to do it.  But it was interesting to read the responses.

I've picked up a IC-718 to replace my 20 year old original owner IC-735....which needs repairs again.  The cost of all the repairs (two trips to Icom and needing a third) for the 735 was exceeding the purchase price of the 718, so I've just decided to replace it.  The 735 lasted 20 years of moderate use before needing any repairs. 
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W8JX
Member

Posts: 5004




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« Reply #9 on: March 31, 2011, 06:45:21 PM »

Just for grins I did a quick search and found mod in less than a minute. It seems 718 shares finals with 775.

http://www.rastforum.com/index.php?topic=80.0

(scroll down)
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K4XZ
Member

Posts: 82




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« Reply #10 on: April 01, 2011, 09:33:23 AM »

Your IC-718 works fine just the way It Is. I agree with all the other posts. Just leave It alone and It will work a long time with no problems. The 718 was my first brand new radio. That was 7 years ago. It still works fine. I use a 746PRO for my main rig sometimes I wonder why, but I still have my good old reliable 718 set up for digital PSK-31 & RTTY. It works great on these modes also. If it ain't broke don't fix It!

  73 Joe Patrick DE K4XZ
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KE3WD
Member

Posts: 5694




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« Reply #11 on: April 01, 2011, 10:32:34 AM »

On top of all of the other already mentioned very good reasons not to attempt to do this, please consider that the Filters, plus any associated switching relays for them, are not very likely to hold up under twice the RF power. 

And if there is a built in Antenna Tuner, likewise.


73
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OZ6ABM
Member

Posts: 24




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« Reply #12 on: April 01, 2011, 12:20:57 PM »

Even better, try to improve the antenna - it pays in the longer term (for all radios)

73
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W8JX
Member

Posts: 5004




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« Reply #13 on: April 01, 2011, 12:38:44 PM »

Or better still a amp,,,,
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KE3WD
Member

Posts: 5694




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« Reply #14 on: April 01, 2011, 06:21:54 PM »

An amp is never a good solution until you have a good ANTENNA system. 

Unfortunately, many cannot do that, for many and varied reasons. 


73
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