This is from mods.dk

"Some FT-100 owners may have experienced what is widely known as the blown SRF 7043 VhF/UhF output transistor or Mosfet final syndrome, which frequently occurs for no apparent reasons. The problem is contributed by Yaesu???s engineer???s lack of fundamental design and forethought.

The blowing SRF 7043???s problem are caused by the following reasons.

   1. Earthing and shielding problems causing self-oscillation and SWR problems.

   2. Insufficient or inadequate air-cooling system for the SRF 7043 heatsink, thereby averting the device???s heat sink to ventilate heat dissipated by idling bios current while in standby operation.

   3. Yaseu either completely ignored or never considered the possibility of Mosfet RF thermal runaways, by not designing prevention or monitoring heat-sensing circuits for the SRF 7043 output stage.

Vertex or Yaesu???s engineers, by adopting some ???quick fix??? modifications, have managed to get around most of these technical problems. These various Yaseu modifications are available on this web site. However, over a long period, the distressed Yaseu engineers have not managed to find the real solutions to these technical problems, which do raise a few questions.

   1. Why did Vertex or Yaesu???s engineers use SRF7043 for output finals when other cheaper and better quality devices such as ???Polyfets??? SK702 and Phillips BLF549 devices were available?

   2. Why did Vertex or Yaesu???s engineer???s use Aluminum instead of Copper material for the finals heat sink, when Copper has greater mass and heat conductivity, and unlike aluminum does not produce the phenomena known as hot spots.

   3. To prevent thermal runaways why did Vertex or Yaesu???s engineers not include a negative coefficient thermal sensitive zenner diode bios circuit, attached to the SRF7043 heat sink? There are numerous university papers and thesis???s on RF MOSFET thermal Bios circuits.

   4. Why did Vertex or Yaesu???s engineers deliberately design the SRF7043 Mosfet RF final stage to be continually running in the Class AB bios mode operation, while operating during standby mode? Taking into the factor of a bios idling current of .4 amps, multiply by 13.2 volts, this equates to approximately 5.2 watts of constant heat sink dissipation. Hence, there is a definite need for a modification to the air-cooling fan system to be continually running all the time. I question the reasons why the Yaseu engineers would design this output stage to be running in Class AB Bios mode continually all the time. Hence in Class C Bios operation, there would be no heat and no blow-ups, because there would be hardly any quiescent current flowing through the TX output Mosfet RF stage. Since the SRF 7043 Mosfet RF device operates in the VHF and UHF bands, mostly in FM mode. There is no technical reason (other then for a small reduction of power output or unless using SSB modulation ) why the SRF7043 cannot operate in Class C Bios operation, all the time. Even in SSB modulation when you have to use Class AB mode operation, you can still use Class C Bios operation for standby mode.

I cannot understand why Vertex or Yaesu???s engineers did not do the following.

   1. Why did Yaseu not make the FT 100 computer programmable? All they had to supply was an inexpensive computer cable and some software. FT 100 can easily handle extra bands (16) and memory; and if you can program them, wow. This computer programming would also bypass the frequency limitations and restrictions, able to set mode and repeater offsets, all within technical limitations.

   2. Why they did not include an inexpensive AM filter and a stable oscillator, making it very saleable item for number of other applications?

The Vertex or Yaesu???s engineers in my opinion did know what they were doing.

The major problem for a number of FT 100 users is experiencing the problem of replacing and obtaining the SRF 7043 MOSFET finals.

To buy a direct Yaseu replacement SRF 7043, costs about $203 in US dollars from Ham outlets. I understand that the S as in SRF stands for shit.

However, you can use the following substituted devices all quoted in US Dollars.

BLF549 80 watts available from Phillips, Arrow and other outlets $153.

MRF166W 40 watts available from Richardson Electronics $83.64

SK701 40 watts, available from Polyfet.com, guessometer price $84

Sk702 80 watts, available from Polyfet.com, guessometer price $98

WARNING, always wear a breathing mask and have a vacuum cleaner handy when removing damaged MOSFET RF devices. You can always use F2 or a rubbery glue, to hold things together when taking out damaged devices. Barium Oxide is a very poisonous substance to inhale. Never dispose of it in landfills.

Stray electrostatic voltages caused by incorrect handling techniques can easily damage these devices.

If you do not know what you are doing, always pay somebody else who does.

After installing the new device, always check the Bios current flowing through the device. The idling current in AB operation should never exceed 0.4 amps*. *0.8 amp in SK702. Use these figures at your own risk. Of course, you can always operate in the safer Class C operation mode. Make sure the cooling fan modification is working all the time. Do not forget Yaesu???s earthing modifications.

For the newbie???s, a thermal runaway occurs when a Mosfet RF device say normally running at 0.4 amps with no ventilation or cooling system, goes above it operating temperature parameters. Consequently, the devices Bios current increases, producing more self heat, and then more bios current, and so on, to point when it will self destruct. By increasing the Mosfets gate into the positive region, increases the current of the device. They have similar characteristics to Pentode tubes, but they are current devices.

Yours truly

Paulus Telfer"

Have not looked into availablity of the replacements mentioned. I am taking very good care of my original.

Jim

There is a different module that is said to work. Some mods required. I don't have info here at work, will check when I get home. Either someone posted it here or I found it on one of the online mod sites.

Jim

I found the manual at mods.dk

Took me about 30 seconds to find the manual online. would you like me to send you the pdf file (190k or so)? BTW the fast/slow switch means "fast=FM, slow=SSB/CW, ATT on/off sounds like the input power level (ON=3watt or less, OFF=5watts

Another trick I have seen, but never used. Take the studs before installing and rip through the middle of the board except for a half a foot or so on each end. Basically converting the 2x4 into 2 2x2s. Then insulate the wall with fiber bats or whatever. I wouldn't recommend it for a load bearing wall though. My shack has poured concrete walls, floor & ceiling with a minimum of 2 inches of foam behind the sheet rock. The XYL uses the intercom to yell at me (and I can shut that off!!).

Jim

With the kit installed and the bandswitch on my 180 in the 18 & 24.5 positions, the display shows only the kHz & Hz digits (the last 4 digits) in the 10 MHz position it reads out all 6 digits. So I would say that your rig has the kit installed. Nice old rig, I should use it more I guess. Seems like I am always using the newer, computer compatible rigs.

Jim

There, it is back today.

You can use about any dynamic mike on it. You need a real 6 pin phone plug with pin 4 to ground, pin 5 to mike audio and pin 6 PTT. Start with mike gain set to around 50 (both SSB & FM) and go from there. Get a local on 2 meters to set the FM on a simplex freq and someone on 2meter ssb for the ssb setting. If you don't have a manual it can be downloaded on line. If you can't find it let me know & I can send it. files run 5meg for pdf manual & 32 meg for pdf tech manual. Nice little radio.

Jim

Read the screen. Too many visitors this month so it went over his bandwidth limit. Check back tomorrow.

Jim

How about feeding it about 66 feet from the house end (Mast on other side of house?) with 450 ohm window line. That would be one to model. I think I will look at that when I get home. It would probably depend on exactly how much wire is on the long end.

Jim

And old answer is to use mast sections that slip together and put a hinge at the back top of the vehicle with a section  above the hinge lying on the roof. When you want to erect it insert the bottom section and push it down to a clamp at the bottom of the vehicle. You then have 1 section above the vehicle. If you use heavy enough masting you might be able to go 2 sections by inserting the third section in the front of the second section before tilting up. It will get a lot heavier though, more so with several antennas on it. If it gets too heavy because of heavy duty mast or multiple antennas use a winch to erect. You have to have a good fabricator, but it is a cheap, simple solution.

K0XU

http://w4emf.gs35b.com/mla2500-retro-gi7/
http://w8slc.w4zt.com/
http://gi7b.com/mla2500/index.html
http://home.comcast.net/~wb8wju/
http://w4emf.gs35b.com/mla2500-retro-3cx800/index.html

Here are a few. I am sure there are more out there.

Jim

Search for "MMANA", this is a freeware program. Works only in meters if I remember correctly, but it should be enough to get you some idea of what you antenna is doing.

Jim

There should be no issues there. I have never had any problems except with the amp. had to keep that at least a foot from the monitor.

Jim

You might try telling them that if you have to give up the radio equipment that you think you will take up heavy metal or grunge. Seriously, it sounds to me like they have some issues like many others that have no understanding of the hobby. And it sounds like the extended family if getting more use of the facilities than you are.
Explain that the antennas are necessary (no antenna = no radio). Try to keep them as neat as possible. And really, what do they want from someone your age, would they rather you were doing drugs and running with a gang? They don't know how good they have it!
Is there an older ham in the area that could take some time to explain some of this to them? Would they listen? I wish I was not so far away, I would come over myself and talk to them myself!!

I wish you luck.
Jim