Icom 745 -Limited RF Power

[AF6LJ]

Originally Posted by AG3Y

Well, if the 745 is old, my 720a must be ANCIENT!

I am sure glad I replaced the finals this past week, I'm having all kinds of fun with it and my "new" Johnson Matchbox and ladder-line fed dipole !


BTW, this is a "rigpix" photo. My rig looks a LOT better !

I knew someone who had one of those radios, they are quite good. If I am not mistaken it's only two or three years older than the 745. I wouldn't consider it ancient, ancient would be a Heath SB-100 anything before that is prehistoric.

[AG3Y]

After replacing the Transistors in the 720a, I set back the total power output to less than 100 watts by raising the ALC voltage with the appropriate circuit board mounted trimpot. I do a lot of 100% duty cycle digital work, and want to keep the same thing that happened to the old finals from happening to the new ones! Right now, the IC meter shows about 9 amperes steady state ( key down CW mode ), and it probably wouldn't hurt if I turned it down even a bit more!

Of course, the RF power level can be controlled by front panel controls as well ( on the 720a, I mean ) and I would advise you to check to see if you have similar controls available in that rig. I bet you do !

Good luck, 73, Jim

[AF6LJ]

Originally Posted by AG3Y

Well, if the 745 is old, my 720a must be ANCIENT!

I am sure glad I replaced the finals this past week, I'm having all kinds of fun with it and my "new" Johnson Matchbox and ladder-line fed dipole !


BTW, this is a "rigpix" photo. My rig looks a LOT better !

Those are very good tuners, when they match they do it in a very efficient manner.
No baluns or other things you don't need.

I love my Johnson Matchbox.

[AG3Y]

A little history lesson here. The 701 preceeded the 720 by a few years. I owned one of those for a short time, too. That radio ended up in South America being used by a Missionary for phone patches. I remember that he had to repair the radio by inserting strands of lamp cord wire through the little feed-through holes in the circuit board, because the high humidity caused the boards to expand, cracking the walls of those holes! Quite a job for someone many hundreds of miles away from civilization !

Unlike the 701, the 720 and the later "A" model feature general coverage receive, and bandswitching was accomplished with the infamous "rotary relay", that makes a "clack-clack" sound every time you push the "band change" buttons.

Incidently, the 720's functions are largely controlled by momentary contact pushbuttons, unlike the earlier radios which had several position rotary switches. It was capable of an early form of computer control ( which I believe I might still have the software for ) but the system was not compatable with the modern implimentations.

Back to the regularly scheduled thread, already in progress!

[AF6LJ]

Originally Posted by AG3Y

After replacing the Transistors in the 720a, I set back the total power output to less than 100 watts by raising the ALC voltage with the appropriate circuit board mounted trimpot. I do a lot of 100% duty cycle digital work, and want to keep the same thing that happened to the old finals from happening to the new ones! Right now, the IC meter shows about 9 amperes steady state ( key down CW mode ), and it probably wouldn't hurt if I turned it down even a bit more!

Of course, the RF power level can be controlled by front panel controls as well ( on the 720a, I mean ) and I would advise you to check to see if you have similar controls available in that rig. I bet you do !

Good luck, 73, Jim

there are the same controls, the 720, 740, and 745 have a great deal of circuity in common. The 745's PLL is considerably different than the other two radios along with a different logic board and feature set.

I had the occasion to aid a friend in troubleshooting a 740 a little over two years ago.

[AF6LJ]

Originally Posted by AG3Y

A little history lesson here. The 701 preceeded the 720 by a few years. I owned one of those for a short time, too. That radio ended up in South America being used by a Missionary for phone patches. I remember that he had to repair the radio by inserting strands of lamp cord wire through the little feed-through holes in the circuit board, because the high humidity caused the boards to expand, cracking the walls of those holes! Quite a job for someone many hundreds of miles away from civilization !

Unlike the 701, the 720 and the later "A" model feature general coverage receive, and bandswitching was accomplished with the infamous "rotary relay", that makes a "clack-clack" sound every time you push the "band change" buttons.

Incidently, the 720's functions are largely controlled by momentary contact pushbuttons, unlike the earlier radios which had several position rotary switches. It was capable of an early form of computer control ( which I believe I might still have the software for ) but the system was not compatable with the modern implimentations.

Back to the regularly scheduled thread, already in progress!

Thankfully the 745 doesn't have any double sided boards.
I always wanted an IC-701. That's old also but not ancient.

[AG3Y]

Icom made at least two, possibly three different radios using the chassis from the 701. I distinctly remember a 6 meter setup, and there was probably a 2 meter rig with the identical appearance. That would have made quite a neat looking station, to have both or three of those radios, either stacked or side-by-side!

[AF6LJ]

Originally Posted by AG3Y

Icom made at least two, possibly three different radios using the chassis from the 701. I distinctly remember a 6 meter setup, and there was probably a 2 meter rig with the identical appearance. That would have made quite a neat looking station, to have both or three of those radios, either stacked or side-by-side!

Here is the 2m radio'

IC-211



This I believe was the 6m radio.



I think this is right.

And fir UHF...



I think that's it....

[N0SYA]

For those of you who have the 720, there are some mods to reduce the likelyhood of solenoid failure, it's in the Nov 95 qst and hints and kinks 14th edition book by the arrl.

Then there's this much more involved one:
http://www.hayseed.net/~jpk5lad/IC-7...y%20Switch.htm

[AG3Y]

I believe there is still a Yahoo! Icom users group. Several years ago, I published the procedure I used to clean and re-adjust the stepper relay used in the Band-selecting portion of the 720a. At that time, there was also a string concerning replacing the rotary relay with a series of standard relays, used to select the proper band-pass filters. It made for a much quiter, and quicker operating radio, but in my opinion, it removed a lot of "character" from the 720 ! I have grown rather attached to that "Clack-clack-clack" over the years !