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Two Older Sony Receivers:
ICF-7601 and ICF-SW7600

By Stephan Großklaß
Home Page: Sony 7600 Series Page (opens in new window)

Today we will be looking at two older Sony portables coming in the handy pocketbook-sized format that has proven to be a good compromise over the years:
The ICF-7601 measures 192.5 × 122 × 35 mm³ (or 7-37/64 × 4-51/64 × 1-3/8 inches), the ICF-SW7600 is slightly smaller at 191.2 × 118 × 32.3 mm³ (or 7-33/64 × 4-41/64 × 1-9/32 inches). Both use a rather powerful speaker that is 7.7 cm or approx. 3 inches in diameter, both are dual conversion designs, and both have been out of production for a good 10 years - but that's where the similarities end.

Both of them will be compared to my faithful old ICF-SW7600G, a well-established model in this class and my first serious shortwave rig. So, what can you expect when buying one of these on the used market?

[Photo]
Four on One Nightstand - from the front, first our two contestants, then the ICF-SW7600G, and finally (more for fun) the old Philips D1835 from the mid '80s. The alarm clock will not be dealt with in this review, but it be mentioned that it's radio controlled - wouldn't you also be with so many radios around?

A look at the ICF-7601

History and Concept

The ICF-7601 is the older of the two, having been made from about 1988 to 1993. Its sales price was some US-$ 129 or so. Apart from the small microprocessor controlling the switch functions, it's 100% analog. It covers mediumwave, the three lowest shortwave bands from 120m to 75m (or longwave, on the ICF-7601L) and FM as a single conversion unit (with an IF of 455 kHz for AM and 10.7 MHz for FM, respectively), the shortwave bands from 60m through 13 m, including 22m (except for the band segment around 19 MHz), are covered with a dual conversion design with a 1st IF of 10.7 MHz +/- 350 kHz and again a 2nd IF of 455 kHz. This dual conversion design is quite interesting, since it uses a fixed (crystal controlled) 1st mixing frequency for each band, so what's varied with the main tuning knob is the mixing frequency for the second mixer. Since this is lower than the 1st mixing frequency (up to a factor of 3 for 13m), better frequency stability can be obtained this way, which is always critical for analogs with their notoriously drifty LC controlled oscillators. On the 1st IF, inexpensive ceramic filters similar to those used in FM IF chains are used to keep frequency ranges outside the currently selected band away from the 2nd mixer; life of the 1st mixer is made easier by antenna tuning circuits switched together with the cystal oscillators. The telescopic whip antenna (about 69 cm in length and with a provision for attaching an inductive antenna coupler) is used for the dual conversion shortwave bands and FM, the other ranges have to make do with the built-in ferrite rod.

Operation

The front of the ICF-7601 is unlikely to overwhelm anyone with its complexity: Speaker grille on the left, scales on the right with some sliders and buttons underneath and a small tuning LED in the upper right. Four of the buttons are used for selecting the SW1 (or LW), SW2-10 (dual conversion), MW and FM bands, another turns the radio off, there's a "hold" slider to disable button operation and last but not least the shortwave (2-10) band selection slider (which looks like it was taken over from an ICF-4900 or somesuch because it's rather small - parts recycling?). On the left side of the case you can find a DC in socket, a mono headphone socket (which is rather stereo friendly) and the usual useless carrying pouch, on the right there's the volume slider (which could be a bit easier to move), the tone switch and the main tuning knob. Ah yes, there's a small stand on the back (a bit flimsy for my taste), right next to a small world time zone map, along with a battery compartment for 4 AA (R6) cells; finally there's a telescopic antenna on top. That's all.

It seems to me that back then the ICF-7601 was Sony's entry-level shortwave rig, similar to the ICF-SW35 today. Indeed, the case construction is not quite as stable as I'm used to from other "7600" receivers, and the receiver concept looks a bit like an ICF-4900 with more bands and features added in a larger case with a larger speaker. Still, analogs with this kind of performance and quality are no longer being made today.

Performance

That's what you've all been waiting for, right?

On FM, sensitivity seems to be good even with no preamp FET used, but selectivity is W-I-D-E. That's not overly amazing with just a single FM IF filter. One should try replacing it with one of Murata's SFT10.7 series filters (these are the equivalent of two conventional SFE10.7 filters at comparable insertion loss), maybe the 180 or 230 kHz variants. Scale accuracy isn't outstanding on my sample.

On mediumwave, the effective sensitivity of the ICF-7601 is so close to that of the ICF-SW7600G that even now I can't decide which one is better in this regard! (One problem is the very different frequency response of both rigs, which makes comparisons a bit difficult.) In terms of selectivity, the 7600G is ahead, but apparently mostly due to its aggressive audio lowpass filtering. Scale accuracy is quite OK.

In the SW1 range, I noticed good sensitivity, though image rejection isn't particularly exciting and I did see some mixing products from higher bands in the 2...3 MHz range. Due to the large range covered, the scale is rather coarse and not a big help on 75m.

On the SW2-10 bands which are spread over approx. 650 kHz each, the scales contain frequency marks in 50 kHz distance; the theoretical frequency reading precision is some 10 kHz which is very good for an analog. In practice, I found that the scale accuracy mostly ranged from spot on to no more than 10-15 kHz off, with larger deviations only encountered near the edges of the bands. This is really good for this kind of set.
Selectivity is not quite as good as on the ICF-SW7600G, but this seems more a result of the latter's much more aggressive audio filtering, since I found it to be almost as good as on the ICF-SW7600 (i.e. 5 kHz separation is quite decent, 9 or 10 kHz away it's almost perfect unless the adjacent station is really strong), which uses the same filter as the newer 7600G but with less tight audio lowpass filtering. I found quite a bit of IF level hiss on the ICF-7601, which could be reduced considerably by switching the tone control to NEWS.

Sensitivity is kind of hard to gather on this set, since absolutely everything connected to it serves as an antenna, in best pocket radio manner. This makes measurements with phones or AC adapter rather unfair. So I had to resort to batteries, where another problem arises: My comparison rig, the ICF-SW7600G, noticeably loses in sensitivity when run off rechargeables. This could lead to the paradox situation of the ICF-7601 even being slightly ahead. All in all, I would say sensitivity is good, up to par with the SW7600G or SW7600 when the band is peaked up right (13m seems a bit weaker than some others on my sample). If you happen to have an ICF-7601 with unexciting shortwave sensitivity and know your way around radios, I'd suggest to obtain a copy of the service manual and do an alignment.

Sensitivity to overload is one area where the 7601 doesn't fare too well. Particularly the 31m band with its very strong signals in the evening (I'm in Central Europe, which is notorious for high SW signal levels) overloads it pretty badly so that only fully retracting the aerial helps. Attach some phones or an AC adapter, and overloading starts again - did I mention using the AC adapter cable as antenna is a real bad design decision? (Not even the old Philips D1835 is that bad, and that's a single conversion design!) Even on bands with medium signal strengths you frequently hear some quiet whistle from an IM product. Well, at least strong signals in one band don't affect the other ones. I did notice some bleedthrough from a local FM station in the lower 31m band; theories as to where this mixing product is created are still being gladly accepted. The reference receiver does not exhibit such overload issues.

Image rejection is fair on SW1 and excellent on the dual conversion shortwave ranges. The reference rig does show some images, maybe due to 1st IF leakage or 2nd mixer leakage.

Apart from the IF level hiss in AM, I like the speaker audio of the ICF-7601, which is just about a magnitude better than on the ICF-SW7600G. Listening with headphones, you quickly notice there's quite a bit of bass expansion going on with the tone switch in MUSIC position, which may be somewhat tiring in the long run.

The ICF-7601 is everything but a battery hog. It should run many hours with decent alkalines, and since it still works halfway well down to about 3 V, batteries can be squeezed out quite well. I don't think rechargeables are needed; if you do use them, be sure to keep a multimeter at hand to check cell voltage in order to avoid deep discharge.

All in all, the ICF-7601 is a good choice for areas with lower signal levels, where its sensitivity will be quite welcome; in a strong signal area you may be annoyed by the mixing products. I'd consider it "tweaker's paradise", since an alignment and FM filter change may help the performance considerably. It sure is a fun rig, but please don't pay insane sums for one.

A look at the ICF-SW7600

History and Concept

The ICF-SW7600 was produced from 1990 to 1993 and usually cost a bit more than US-$ 200. It was the successor to the venerable ICF-7600DS (ICF-2003), which in turn had been little more than an ICF-7600D (ICF-2002) with different colors, the revolutionary little receiver from 1983. In this case, the improvements over the older models were present but not spectacular; rather a key design guideline seems to have been effort and cost reduction while retaining or improving performance.

The ICF-SW7600 is clearly less complex than its predecessor, which can be seen not only in the reduced number of PCBs but also the missing meter band display and the lack of a clock display while the receiver is running. It also shows a much higher degree of integration, which is not surprising given it was introduced seven years later. Performance did not suffer except for FM, in fact the audio is better and AM reception is generally less noisy. Battery life particularly in FM could be noticeably improved, a sideband choice for SSB was implemented and it was possible to do away with the backup batteries.

The ICF-SW7600 is a PLL synthesized receiver tuning FM (in stereo via headphones) from 76 to 108 MHz or 87.5 to 108 MHz with 100 or 50 kHz steps or AM from 150 kHz longwave up to 29995 kHz shortwave continuously (on most models), with 3 kHz steps on longwave, 9 or 10 kHz steps on mediumwave (selectable via a switch in the battery compartment; doing so clears the memories) and 5 kHz steps on shortwave. (Panasonic already offered 1 kHz steps in the RF-B65 back then.) On FM, it's the usual single conversion design with a 10.7 MHz IF using two nominal 280 kHz IF filters (and, BTW, an RF preamp FET), for the AM ranges it's a dual conversion receiver with a 1st IF of 55.8425 kHz (a crystal filter is used here) and a 2nd IF of 455 kHz (with a 6 element ceramic filter, Murata SFR455I). A product detector is provided for SSB reception, with two different carrier insertion frequencies to give preference to the upper or lower sideband. For shortwave and FM, the telescopic whip (about 69 cm in length) is used, LW and MW are received via the ferrite rod.

Operation

The front panel is neat and tidy: Speaker grille on the left, display and buttons on the right. Above the display you can find the obligatory tuning LED, below it there's a little table (with only mediocre readability) showing the frequencies of the various shortwave bands. The display itself shows the frequency if the receiver is on or the time if it isn't, it also displays the number of the currently chosen preset and indicates the operation of the sleep and standby timer functions, if applicable. Right next to the display block sits the numeric keypad with the keys for direct frequency entry; in the upper right there is the sleep timer button (which turns off the radio after approx. 65 minutes) next to the on/off slider and switch. The latter functions the same way as on the newer ICF-SW7600G - if the slider is in position LOCK, the radio just shows the time and otherwise cannot be operated; this is done to avoid accidental battery depletion. On the bottom, five buttons are neatly organized in a row, with most of them having a second time or timer related function when the receiver is off but not locked: ENTER for saving memories (doubles as time set button), BAND (doubles as standby timer set button) for band switching together with the somewhat small pair of tuning keys next to it, the scan tuning start/stop button (also used to enable the standby timer) and last but not least the small key protect button which is used to lock the buttons to avoid accidental frequency changes and such.

The left side of the receiver shows a DC in jack, headphone (stereo), line out (mono), tape control and possibly external antenna (not on my sample, silly postal regulations) jacks along with the attenuator switch and finally the usual useless carrying pouch.
On the right side you can find the volume control slider (easier to move than on the ICF-7601, though a smooth wheel is yet better), tone switch (the usual NEWS/MUSIC choice), AM mode switch (selecting between AM operation without fine tuning, AM with fine tuning, LSB and USB) and the fine tuning wheel (which varies the frequency by about +/- 8...9 kHz on my sample, which is a bit much for my taste).

Finally, the top of the receiver contains a small light button for momentary lighting of the display, and on the back you can see the battery compartment for 4 AA (R6) cells and a rather big, stable flip-out stand with a world time zone map on it. Phew.

While I did like that you can cross rather large frequency areas quickly thanks to the 5 kHz steps, some people may be annoyed by the chuffing associated with quick tuning. (Continuous reception wouldn't make much sense at least on AM, that's why the audio is muted upon retuning.) I found the frequency entering concept with the separate buttons for AM and FM to be somewhat weird, given the strict separation is not mirrored anywhere else. Standby timer operation is limited to the last frequency tuned to, unlike in later models which have separate presets for this. Like in the 7600G, the scanning function on FM only looks at signal strength and will stop a few times on a stronger station. The receiver features the luxurious number of 10 presets which can be randomly used for either FM or AM stations.

Performance

FM performance is nothing to write home about - sensitivity is noticeably lower than on my 7600G in spite of the latter's modified filters with higher insertion loss. The stereo threshold, however, seems to be lower, but this might also be caused by the reference receiver's narrower filters (I had them changed to 150 plus 110 kHz, which improved selectivity dramatically) which cause higher distortion. Selectivity is not really awe-inspiring either, as to be expected from the two 280 kHz barn doors (but hey, it's better than with only one). I found what appeared to be some sort of mixing product or spurious response from a strong local station on 101.8 MHz on 96.5 MHz; this was not present on the 7600G. Overall, I'm not too surprised that at one time a new proud owner of an ICF-SW7600 wrote that his old ICF-7600DS (or ICF-2003) had been better on FM, apart from stereo of course.

In the AM ranges, it gets much more interesting. Sensitivity on mediumwave proved to be near identical in both the ICF-SW7600 and ICF-SW7600G, i.e. pretty good in this receiver class. This continued in the shortwave bands when both receivers used the same AC adapter. With both running off rechargeables, the sensitivity on the higher bands seemed to be better on the older model at first, but in the end the sensitivity varied far more greatly as a function of the supply voltage than between the two. Antenna tuning could partly be improved on both models by using the simple ADDX-PRE-1 antenna tuner / preselector. Mixing products were a tiny bit harder to produce on the SW7600 than on the newer model. Maybe this is related to the somewhat higher supply voltage for the FETs in the 1st mixer and lower supply voltage for the preamp FET, who knows. Image rejection proved to be identical in both models, i.e. approx. 30-40 dB for +910 kHz. (Again, I had not expected this. The measurements taken by Radio Netherlands suggested the SW7600 should be noticeably worse.) Selectivity is not quite as good as in the 7600G, which probably is related to audio filtering, since the IF filter used is the same. The SW7600 is a tiny bit ahead of the 7601 (i.e. 5 kHz separation is quite decent, 9 or 10 kHz away it's almost perfect unless the adjacent station is really strong), but lets much less IF level hiss come through. The SW7600's frequency response is much easier on the ears than the rather muffled audio of the 7600G.

SSB demodulation works rather well, with nice, clean audio, though there is some distortion on the first syllable with very strong stations (a rather common AGC related problem). Unlike in newer models, SSB is not really sideband selective - the LSB/USB setting only alters the frequency of the inserted carrier so that more of the desired sideband is inside the frequency range the filter lets get through, but you can still tune both sidebands that way and may be bothered by stations on the opposite sideband you did not want to hear. The lack of any sideband separation makes ECSS (listening to AM stations in SSB) pretty much impossible (even if you can get close to the carrier, the volume will be oscillating with a beat tone), which is too bad because the SW7600 does not feature synchronous detection yet (of course). The fine tuning range is rather huge at some +/- 8...9 kHz on my sample, which not only makes clarifying SSB stations a bit tricky (though certainly doable) but can also lead to the listener finding himself more than 5 kHz away from the displayed frequency - as if 5 kHz steps alone didn't make precise frequency readings for SSB hard enough.

In terms of speaker sound, the SW7600 can pretty much keep up with the ICF-7601 (i.e. it's noticeably better than the 7600G); the audio via phones is rather nice with good bass, only the highs on FM are a bit lacking in comparison with the 7600G and other equipment.

While I have not evaluated battery usage - which is likely to be similar to that of the 7600G - I can tell you that there is no battery warning and that the receiver still plays decently on only 3 V. You'd better have a voltmeter at hand when using rechargeables to avoid deep discharge.

Overall, the ICF-SW7600 is quite a nice older portable with good AM RF performance, though its features are rather dated by now. Anyway, if you aren't bothered by the once-typical AM distortion (meanwhile, I'm somewhat spoiled by synch detectors, particularly the one in the AR7030) and don't listen to SSB very frequently, this one might be for you. (To be fair, the synch detector in the 7600G does not help a great deal with selective fading distortion and rather prefers to unlock upon severe fades. It is nice for sideband selection, though. AFAIK the 7600GR features improved synch detection.)

ICF-SW7600 trouble spots

And now for something completely different... failures, that is. You may know that electrolytic capacitors are no infrequent trouble spots, and they're even more likely to be if they aren't treated properly. The filtering cap in the DC/DC converter that generates +15 V - C127, a 22µF 6.3 V part - is such a case. The DC/DC converter operates at a rather high frequency of almost 2 MHz, and that poor cap has to take all the ripple it generates, which heats up the thing and leads to faster aging in the end. Later models contain a small ceramic cap in parallel, which takes care of the high-frequency ripple. Symptoms of C127 failure are a PLL that only locks slowly or even fails to lock with a noise similar to that of a machine gun (which is caused by the PLL unlocking upon a voltage drop on the +15V line which in turn is caused by the DC/DC converter being unable to supply enough current). An underperforming C127 may also cause trouble on FM alone, which may be remedied by exchanging C69 (Vcc buffering cap for the CXA20111, 220 µF 4 V) - apparently the current draw from the DC/DC converter is largest on FM because of the varicap diodes used for tuning (otherwise +15V is only used for PLL related functions). I suspect most frequently used ICF-SW7600s will face C127 related problems in the long run. Problem is, you have to be pretty good at SMD stuff to repair this.

See my Sony 7600 series page for more details (opens in new window).

 
 
 
 
 
 
 

   

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