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Author Topic: IC-R70: Icom's forgotten gem  (Read 18298 times)

Offline Muskrat

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IC-R70: Icom's forgotten gem
« on: May 08, 2014, 0937 UTC »
The ICOM R70 was produced for only two years.  Today it is nearly forgotten.  Introduced in 1982, it was the flagship of Icom's line of radios, and the only serious competitor to Japan Radio Corporation's NRD-515.  It was the father of the infamous R71a, and the grandfather of the popular R75.  It was a triple/quad conversion receiver and shares it's basic RF/IF circuits with its offspring, as well as the receiver section of the ICOM 751a ham transceiver.   The radio was literially built like a tank, and was used by many top US Govt. Agencies, including NSA, and the FCC.  The chassis as well as the face and cabinet is solid steel, no plastic cabinets here!  The radio consisists of six separate, interconnected, conventional circuit boards.  No surface-mount components make this radio easy to service and restore.  When introduced in 1982, it was touted for featuring no less than thirty-six control knobs and switches.  This receiver is a knob-fiddler's dream!  The rig has every feature found on the well respected R71a, except direct frequency key input, memories, and variable noise blanker.  It does feature a two-step noise blanker though.  It also features a user adjustable reference oscillator useful for precise frequency calibration.  As the radio ages, this control makes it easy to put the radio on frequency.  The florescent green display shows the received frequency to 100hz.  Since there are no memories in this receiver, it has no volatile memory to die when the battery fails, like its later (improved?) offspring.  The triple/quad conversion makes this receiver ultra sensitive, and ultra quiet.  With no antenna connected, and the RF gain and volume controls full up, it is hard to tell the radio is even on.  The front-firing speaker, while not hi-fi, is far better for general listening than the top-firing speakers of Icom's later radios.  Of course for serious listening a good set of headphones is a must.  The radio was also designed to be used in a ham shack, and besides having a ham band only mode, it also has interfaces for interconnection with a transmitter, with the ability to monitor your own transmissions.  But, you ask, how well does this old soldier perform, compared to newer offerings?   By using the same IF strip as its offspring, it has the same filter options, including the popular FL44.  Stock, the radio has an AM bandwidth of 6khz, and a SSB bandwidth of 2.3 kHz.  Also, because of the excellent zero-beat, you can also use the SSB mode on AM stations in crowded band situations.  With the variable notch filter, and passband tuning, this is my go to rig for the difficult ones.  Its sensitivity is on par with the R75, with little noticible difference.  If I want to just listen to a favorite station, the Grundig Satellit  800 is my radio of choice.  But for the rare DX, it is the R70.  With all the advantages of the well-renowned R71a, and none of its disadvantages, this is a real gem.  The only problem with this radio is its little tuning quirk at band edges in general coverage mode.  This is well documented in the manual, and on several websites.  It is only a minor problem, and after a week or so of use, easy to adjust to.   Mine is now thirty years old, and I do not doubt it will still be running strong long after I am gone.  If you see one of these classics at a ham fest, eBay, or yard sale, grab it!  You won't be disappointed.
« Last Edit: May 08, 2014, 1026 UTC by Muskrat »
Grundig Satellit 800, Grundig 450DLX, DX 440, Icom R70, 55ft random wire, built-in telescoping antennas, home-brew Slinky dipole. Central Indiana.
Please send QSLs to muskrat39@hotmail.com

Offline BoomboxDX

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Re: IC-R70: Icom's forgotten gem
« Reply #1 on: May 09, 2014, 0030 UTC »
Nice article, Muskrat.

Never have tried any of the Icom models, although they used to sell Icom ham rigs at a local ham store that closed about 15 years ago. 

I always thought the early Icom ham rig, the 701, was a cool radio, though.
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Offline ChrisSmolinski

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Re: IC-R70: Icom's forgotten gem
« Reply #2 on: May 10, 2014, 1647 UTC »
I have an R71A, and while I don't use it much anymore, I agree it was a great radio in it's day. Two main issues:

1. The volatile memory that, when the battery died, also made the radio non functional. Not too much of a big deal, as there were third party solutions. I bought one, I don't recall the name of the company, but it was not that expensive. It gave you additional memories in banks, and if the battery did die, the other important data required for the radio to function was not lost, as it was moved to non-volatile memory.

2. Icom used really crappy trimmer caps in the VCO. After many years, they fail, causing the VCO to not lock over certain frequency ranges. My Icom IC-735 also suffers from this.  I am not sure if the R-70 is affected by this as well, or not. The Icom R-7000 VHF/UHF radio is not affected. You can replace the trimmers, but it is a pain. Another easier short term solution is to tweak the trimmers back and forth about once a year to clear the crud from the wiper.

Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
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Offline Tom S

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Re: IC-R70: Icom's forgotten gem
« Reply #3 on: June 17, 2014, 0313 UTC »
I agree with the trimmer caps comment.  IIRC there were four of them for four different frequency ranges, and when I bought my R71A one of the bands wasn't working until I tweaked the cap.  Seemed like every so often I had to tweak them, and temperature was a factor.  Seemed like I had to tweak them when the seasons changed from warmer to cooler and vice versa.

Mine had the remote control but I rarely used it since the radio was right there on my radio desk.
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Offline sat_dxer

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Re: IC-R70: Icom's forgotten gem
« Reply #4 on: June 19, 2014, 1639 UTC »
Here's the trimmer problem in action on this model:

http://www.youtube.com/watch?v=MxUuqg88wnY

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