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Thread: Icom IC-751/751A

  1. #1
    Administrator ad4mg's Avatar
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    Icom IC-751/751A

    The IC-751 and IC-751A HF transceivers, mid-range rigs when introduced, still offer excellent value to new hams as a first rig, and seasoned hams as a backup, or even a primary rig. I personally still have my IC-751, bought in 1992.

    Both cover 10m-160m, including WARC bands, and run 100 watts CW/SSB/FM, 40 watts AM. Both rigs sport excellent receivers, quad conversion, if memory serves me right.

    The '751A had a few improvements over the '751, most notably a CW keyer. Both were available with optional internal switching power supplies. My '751 was powered most of the time by an Astron RS-35M linear power supply, although it had the built-in switcher. I found the rig ran pretty warm when using the internal supply.

    There are a couple of inherent problems with these rigs ... one being the problems with the capacitors in the PLL circuit. Any authorized Icom repair center can perform a PLL circuit upgrade. There also seems to be problems with a voltage regulator IC that powers the display. Mine currently suffers from this issue, and I have to turn it on about 30 minutes before I use it, and recycle the power after that short wait before the display will work.

    Additionally, the BIOS and ROM in both rigs is battery-backed. Allowing the backup battery to completely die causes the rig to be totally non-functional. I believe there are aftermarket BIOS/ROM boards available for these rigs that solves the issue. On the factory BISO/ROM board, the battery replacement procedure isn't for the feint of heart. When I replaced the bias, driver, and final amplifier transistors in my rig, I also replaced the backup battery. It basically consists of soldering the new battery in place before removing the old one!

    In spite of these issues, the radios are readily available at reasonable prices, and if they have been taken care of, they still are capable of providing years of service. Again, on the receiver, after 16 years of operating, I have yet to locate another HF rig that has a more sensitive, and quiet receiver. The transmitter is quite capable, and if the cooling fan is in working order, the duty cycle is quite high. The only reason I had to replace my finals was due to an amplifier malfunction that obviously threw some DC current back via the antenna connector.

    I'm no rocket scientist, so forgive the rather simplistic review. If I can locate the owners manual for the rig, I'll post the specifications later.

    73,
    Luke
    QAnon / GOP Republicans mentally lack the necessary intelligence to even tell a decent lie (Ex: A cabal of Satanic, cannibalistic pedophiles run a global child sex trafficking ring and conspired against former President Dotard dRUMPf during his term in office... Jewish space lasers, etc.). What in the hell makes anyone believe these melon heads can actually govern?

  2. #2
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    Re: Icom IC-751/751A

    Hi Luke, I agree with you about the 751A - I was thinking it also had a significantly improved receiver over the 751, but then again I'm an old guy and easily confused!

    73,
    Tad Danley, K3TD
    EM10dq

  3. #3
    Administrator ad4mg's Avatar
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    Re: Icom IC-751/751A

    Quote Originally Posted by k3td
    Hi Luke, I agree with you about the 751A - I was thinking it also had a significantly improved receiver over the 751, but then again I'm an old guy and easily confused!

    73,
    Hi, Ted. I'm pretty sure they shared the same receiver. I also remember the '761, although in a bigger case, also had similar, if not exactly the same receive circuitry.

    For some odd reason, I like the movement of the meter on the '751. It seems unique, and the AGC attack rate is just right on receive, making the movement of the meter very eye-pleasing. Odd what quirks of a particular rig stand out ...

    Soon to be 52, I'm no spring chicken either! :shock:

    73,
    Luke
    QAnon / GOP Republicans mentally lack the necessary intelligence to even tell a decent lie (Ex: A cabal of Satanic, cannibalistic pedophiles run a global child sex trafficking ring and conspired against former President Dotard dRUMPf during his term in office... Jewish space lasers, etc.). What in the hell makes anyone believe these melon heads can actually govern?

  4. #4

    Re: Icom IC-751/751A

    I have a IC-751 that I bought somewhere around the mis 80's. I have been well pleased with mine.

    The old memory board will eventually die due to battery if you don't replace the battery every decade or so. I was lucky to get 20+ years out of mine. If you replace the battery before it dies you are ok but if the battery dies the radio will no longer work and the board will need to be reprogrammed after battery replacement. There are are a few upgrades available to replace the existing board.

    * PIEXX ICOMPROM
    http://www.piexx.com/index.php?main_...products_id=26

    * WILLCO ICM-1024B
    http://www.willcoele.com/my1B.htm

    * EPROM/RAMBOARD from IK2RND
    http://ronhashiro.htohananet.com/am-...-ramboard.html

    I went with the ICM-1024B. Delivery was quick and th installation is simple, especially if you don't utilize existing buttons for the extra memories. It is really nice to have 1024 memories.

    IC-751 Manual

  5. #5
    Administrator ad4mg's Avatar
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    Re: Icom IC-751/751A

    Excellent references, Larry! Thanks for posting them.
    QAnon / GOP Republicans mentally lack the necessary intelligence to even tell a decent lie (Ex: A cabal of Satanic, cannibalistic pedophiles run a global child sex trafficking ring and conspired against former President Dotard dRUMPf during his term in office... Jewish space lasers, etc.). What in the hell makes anyone believe these melon heads can actually govern?

  6. #6
    Administrator N8YX's Avatar
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    I am going to be joining the IC-751A ranks shortly.

    x2.

    As much as I like my Cubics and Drakes, they're being shelved in favor of two -751A/R-71A/IC-2KL/AT-500 lineups.

    Plans are to slave the transceiver and receiver together. A custom PIC solution which would emulate Icom's IC-7072 interface is one possible solution. The -7072 was used for transceive operation when running the IC-720A/R-70 combo. Unfortunately, the same low-level CPU interfaces don't exist on the later equipment so I'll have to rig something up via the CI-V port. Another possibility is to use HRD or similar rig-control software.

    I should have done this a long time ago, but tinkering with the older stuff has been fun. Will post thoughts and impressions when the equipment is up and running. It'll be my main 80-40-20M QRO rig so if we Islanders set up a sked there's a very good possibility you'll get to hear the Icoms in action.
    "Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."

  7. #7
    Administrator N8YX's Avatar
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    Quote Originally Posted by ad4mg View Post
    ...Again, on the receiver, after 16 years of operating, I have yet to locate another HF rig that has a more sensitive, and quiet receiver.
    I now have a little bit of run-time on mine and I'll attempt to give some impressions, thoughts and on-air experiences:

    First...in regards to the receiver, I have: The TS-940S. But not just any '940 - you're looking for one in the 7+ million serial number range, the computer-control board (if fitted) should be Kenwood's IS-232 unit and one ought to look for a YK-88S1 SSB filter to replace the '940's narrower S2 unit. The Kenwood hears unbelievably well, but the Icom is right there with it.

    I'm a big fan of sub-receivers. They come in handy for lots of things such as spotting, allowing one to use a different mode/filter arrangement than which the companion transceiver is currently running...diversity reception, etc. The '751 allows this sort of flexibility but non in a master-slave (tracked tuning) configuration without a little bit of work. Namely, computer control or a PIC/Stamp-based I/O controller which actively polls one unit then sends the data to the other.

    My '751 has an R71A connected to it. Ultimately I'll design and build the transceiver adapter which is required for track tuning or I'll use HRD, N1MM or another CAT program to perform this task.

    Impressions: A nice, solid, simple-to-use, non-menued transceiver. Mine looks like it'll require a WillCo board so I'm planning to order two of them: a unit for the current rig and another for its future companion. I want a pair of these, one on each side of the current SO2R position. I lucked out and found an honest seller who didn't strip the filters out of the rig before it was sold to me. As a result, it has a full complement - 2.8/2.4 KHz SSB and 500/250hz CW. I'm planning on buying an Inrad 1.9KHz filter for each of the R-71As in order to give me a little bit more selectivity when operating SSB in contest or DX mode.

    Got on the air with our local 10M contingent last evening and everyone loved the sound of the rig. Nothing fancy in the way of a mic, just an SM-6.

    What makes this setup really work is the system. That is, add the IC-2KL and AT-500 to the trans-receiver pair and you have a 600w, all-band HF communications solution that is capable of automatic band switching, antenna selection and antenna tuning based on transceiver band setting. It doesn't take up a huge amount of real estate, either: The entire affair spans a mere 55 inches of desk.

    I would do this again in a heartbeat. In fact, I'm going to...and find one more piece as a spare, the IC-2KL "Export" (w/ factory-labelled 10M band switch position) model. I really like my other gear - the Drakes, Cubics, Yaesus and all the rest I've acquired over the years - each is a stellar performer in its own right. Space, however, is currently at a premium and I need to reduce the footprint of each operating position. The 751 does the job in spades. By itself it's good. Paired with the rest of the equipment: A K3 could beat it but not by much.
    "Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."

  8. #8
    Master Navigator W5IEI's Avatar
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    At one time I had the 751 A/2KL/At 500 setup myself.
    I loved it on the bands 20,and above.

    I have a local noise problem here with oilfield telemetry that renders some rigs useless on 40,and below when the noise blanker is on,and turned on high enough to
    deal with the noise.
    The 751 A was one of those.
    I still say,it's an excellent rig because of the way it worked on the higher bands when the NB wasn't needed.
    I only currently have two rigs that can handle the noise completely with zero ill effects.
    The Orion II,and the Yaesu FT 102.(The Orion 1 was able to also)

    When I think about it,those are the only two rigs I currently have without synthesizers,hmmmmm.
    Glad you like your setup,it sounds sweet!
    Ummmm, no I'm not peeing in my gas tank :)

  9. #9
    Administrator N8YX's Avatar
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    The Orion II...hmmm. I wish that TenTec would offer a set of transverters and companion solid-state tuner/amp for that rig. I would buy one in a heartbeat.

    That blanker issue is one of the reasons why I'm using a dual receiver setup in the shack: I can modify the gating characteristics of the R-71A's blanker circuitry and make it more useful on wide-band hash...or I can feed the wideband IFs of both into a differential amplifier/detector and essentially eliminate the hash at that stage. Thus far I haven't experienced really bad QRN/RFI issues here.

    Just bought another am/tuner combo and am working on a second '751. Those will go into storage as backups until I get the "big" shack built.
    "Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."

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