Radio Shack's Superadio clone -- the OPTIMUS 12-603

THE STORY OF A RADIO SHACK SUPERADIO CLONE

The Radio Shack Optimus 12-603, a 1990's era Superadio-style radio. I took this pic while the radio was actually playing a station, either local 1590 KLFE or 1600 KVRI, which plays South Asian music.

Being a radio nut, I have a few radios, as is obvious from my posts here on my blog about them. And one of the classic radios used for MW/AM radio listening and AM band and FM band DXing (distance listening) is the GE Superadio.

I have several Superadios: a Superadio 1, a Superadio II, and a working and non-working GE Superadio III (my working SRIII is a very good performer -- the non-working one was hit by saltwater when I took it on a boat once). The GE Superadio was produced from 1979 until the early 2000's some time -- GE sold the brand to RCA, and some of those Superadios were a bit hit-and-miss. But the early ones, from 1996 and earlier, were as good as AM and FM gets. The only thing missing was stereo on FM. The audio was excellent, battery life terrific, and the radios would pull in any station worth hearing.... Well, almost.

At the time of the Superadio's heyday there weren't many, if any, competitors. Some boomboxes were good sounding on both the AM and FM bands, and pulled in distant stations, but aside from that, the Superadio was about it if you wanted a good sounding, high-performance radio for the house, jobsite, emergencies, or to take camping.

A close up of the Optimus 12-603's tuning dial. A bit more high resolution 'log scale' than the GE Superadio III's dial. 'Log scale' dials were used in analog days when dials could be off by 10 or 20 KHz or more, and the ruler like 'log scale' provided a bit more accuracy for logging the station's dial position in a log book. Most people just ignored the 'log scale' and memorized where the stations were. :-)

ENTER THE OPTIMUS!

Some time in the mid 1990's, when Grunge was still king, conservative talk began to rule the MW/AM daytime radio airwaves, and Art Bell was THE nighttime radio show here in the U.S., Radio Shack came out with a new "super radio" of their own, the Optimus 12-603. The official name for the radio was "Tuned RF AM-FM Extended Range Receiver", which was written along the top of the radio. A classy looking black badge with OPTIMUS across the front of it graced the lower left corner of the grille.

Optimus was Radio Shack's brand name for at least some of their stereo and audio equipment, and with this particular radio the Shack decided to put that brand name on an AM/FM radio -- temporarily ditching the Realistic brand name.

When the 12-603 came out, a lot of DXers thought that perhaps the Optimus 12-603 was a GE Superadio in Radio Shack labelling. After all, the two radios look similar: a large black case, big tuning knob on the right side of the case, three silver slide switches on the front (Wide/Narrow, AFC, and AM/FM bandswitch -- just like the GE Superadio III), and three audio controls (Treble, Bass and Volume -- also just like the GE SRIII).

The Optimus had a stylish, sleek looking analog tuning dial, a black metal grille, and the casing was high-impact, black plastic -- which was classic 90's styling. All-black plastic radios were popular in the 1990's. I have a 90's era Panasonic clock radio, a 1991 boombox, a 90's era Sony Walkman, and a few other such electronic gems from that era which all were in black regalia. In this case, the Optimus 12-603 was no different.

The receipt I found in the back of my Optimus. $49 for the radio itself. November, 1996.

A pic of the Radio Shack where I bought my Optimus TRF 'superadio' in 1996. By the time this pic was taken in April, 2018, the store had already closed. :-(

BUYING THE RADIO IN '96

After seeing the radio in the local Radio Shack store (now just an empty storefront, unfortunately), I finally chipped in the $55 to buy one and a set of batteries. I still have the receipt: I bought it on November 5th, 1996.

When I got the radio home, I discovered that although the Optimus was a good radio, it wasn't quite as 'hot' as the GE Superadio. First, the comparative volume was a bit lower, and on the AM band the AGC was a bit tamer than that of the GE Superadio III. The volume between distant stations (like regionals) and local stations was more pronounced. On a GE Superadio, the difference in volume isn't that great between local stations and strong regionals, because Superadios have fairly hot AGC (automatic gain control).

Secondly, on the Optimus, the sensitivity seemed to fall off a bit above 1600. It still brought in local Top Band (X-band) stations, but not as well as the GE SRIII did. The sensitivity and selectivity seemed were good below 1600, though, with the GE SRIII having a definite edge band-wide and a definitely 'hotter' sound overall.

My Optimus 12-603 with the front off. You can see the wires connecting the main PCB (on far right) to the 4 inch, 8 watt capable speaker. The yellow circle is around a small flat-head nail I used to secure the handle after the original plastic peg holding it together broke, a long time ago.

MY REFRIGERATOR RADIO

I used my Optimus from time to time, and then after a while, it fell by the wayside. I took the back off once to try to modify it, after reading about a mod on the internet -- this was probably 2001 or 2002 or so. The mod sucked (made performance worse!), so I undid it, and put the radio back together. I also broke the handle by accident -- I can't remember how or when. I fixed it by supergluing a nail to the inside of the case, to hold on one side of the handle. It still works well that way. :-)

For probably ten years the Optimus was my kitchen 'refrigerator' radio -- mostly unused, gathering dust atop the fridge. Very sad, I know.

Last night, after seeing it up there, covered in dust and some kitchen grime, specks of dirt on the whip antenna, and looking a bit unappreciated and forlorn, I took it down. I cleaned off the dust with a paper towel and spray cleaner, plugged the radio in, and fired it up.

The inside of the Optimus 12-603, with the front off. The main PCB can be seen, with "Super Radio" printed across the top, along with "City", possibly the Chinese manufacturer. The round, metallic device at the upper left corner of the PCB is the tuner control, which was a bit dirty or oxidized, and needed a shot of Deoxit. The main chip, which is the heart of the radio, is the long black rectangle, right center.

IT FIRES UP!

I pressed the power button. And it worked! Tuning was a trick, though. The MW stations in the middle of the dial would lurch and heave and garble -- it was like something was haywire with the tuner, as if it were jumping around incrementally. Obviously, the potentiometer that operates the varactor diode tuning was acting up. Probably dirty, with some oxidation or dust inside. Exercising it helped a little.

Finally, I decided to "fix" the issue the right way: I took the radio's back off and squirted some Deoxit into the control, and worked it back and forth with the tuning knob. Problem solved. In the process, I looked over the radio, and took some pictures of the inside.

Although some of the later, varactor-tuned GE Superadio III's had issues with their tuners, it's not the case apparently with the Optimus 12-603, as they reportedly all had good components inside the tuning circuits. Since I hit my Optimus's varactor tuner pot with Deoxit, I've had no problems.

That said, if you have an Optimus (or GE Superadio) and it hasn't been played in several months, it's a good idea to run the tuner control from 520 to 1700 and back a couple times, to clear any oxidation in the varactor tuning's potentiometer. I've done this with my Optimus periodically after periods where I didn't use it for several months.

A close up shot of the heart of the Optimus radio -- the LA1260 IF chip is circled at top, the UPC1213 AF audio chip is upper right, and the FM Front End chip (amplifies FM before it gets to the main circuits) is circled at lower left.

A REALISTIC TRF CLONE INSIDE -- WITH VARACTOR TUNING

The Optimus is a standard TRF with varactor tuning instead of a tuner capacitor -- in some respects, it appears to be a simpler version of a GE Superadio III. But that's where the resemblance ends. On the inside, it's more like some earlier Radio Shack AM-only DX radios.

In reality, the Optimus 12-603 more resembles the last of the Realistic TRF models -- the Realistic 12-655 and 12-656. It is very similar in circuitry, except the Optimus is varactor tuned, and it has an IF chip instead of discrete transistors in its IF circuits. I have both of the famous TRF models, and the Optimus most resembles the later, 12-656 model -- the Optimus has a similar loopstick (130mm versus the TRF's 140mm), a similar FET RF amp, two IF cans (two stages of IF filtering, versus three in the 12-656), and an AF chip for audio amp and mono audio output (also similar to the 12-656). It has similar selectivity and sensitivity to the 12-656 (the more famous 12-655 was a hotter AM radio).

The 12-603 also is similar to its predecessor, the 12-650 AM-FM TRF, which was a big silver cased thing that had similar circuitry -- the main difference being a bipolar junction transistor in the RF amp stage, different IF chip, and a ceramic filter / IF can combination instead of two IF cans in the IF stages.

The Realistic TRF 12-656, the radio probably used as a template for the MW/AM circuitry in the Optimus 12-603. 130-140mm loopstick, FET RF amp, Converter stage, three IF cans with IF amplification, detector, and into an AF chip for audio. This particular TRF had a tone switch -- the Optimus has two tone controls. The two radios (12-656 and Optimus) perform similarly.

A schematic diagram of the Realistic TRF 12-656. The Optimus circuit is basically similar, except there are connections for varactor tuning, and it uses an IF chip instead of Converter and IF amp transistors. The 12-656 has what appears to be the same 140mm loopstick and one extra IF can (three versus two in the Optimus), and the Optimus has an extra stage of RF amplification in the LA1260 chip. Both have a mono AF audio chip, and mono headphone output. Both have an external antenna connection that is coupled to the loopstick. Unfortunately, there is no schematic available for the Optimus that isn't proprietary, so I can't show it here. One can be found on the Earmark Superadio site linked below in this article.

A schematic diagram of the Realistic 12-650, their first AM-FM competitor to the GE Superadio. It is similar to the Optimus 12-603 which succeeded it. AM, FM (mono), IF chip, although it has three IF stages -- with the 12-650 having an IF can / ceramic filter /  IF can combination instead of two IF cans like the Optimus does. Obviously, there are only so many ways to wire a TRF AM radio. One can say that all of these radios: 650, 603, the earlier TRF's, and the GE Superadios, are all similar. But it looks like Radio Shack merely updated its earlier radios with varactor tuning and a nice, black case to make the Optimus 12-603.

The conclusion I reach is that instead of being a GE Superadio clone, the Optimus is probably more properly described as a Realistic TRF clone! It looks like a combination of earlier Realistic TRF radios, with varactor tuning and an IF chip.

Another major difference for the Optimus, of course, is that it also gets FM, and it has two tone controls, and tunes the MW/AM band as high as 1700 Khz. Perhaps the fact that the Optimus is not as hot above 1600 is a further indication of its Realistic TRF heritage.

AN OVERVIEW OF THE CIRCUITS INSIDE THE OPTIMUS

The IF chip in the Optimus 12-603 is a Sanyo LA1260, which is used in a lot of hot radios (the CCrane EP being one of them). The LA1260 has a fairly robust MW/AM RF amp built inside it, which is probably the reason LA1260 equipped radios work so well on the AM band.

Along with the hot LA1260, the Optimus has an FET transistor for MW/AM RF amp, which gives AM band signals an extra boost. The IF filters consist of two IF 'cans' strung together, which give the radio wider selectivity than a GE Superadio, which has four IF 'cans'. The Optimus's FM section has a 'Front end chip" which I couldn't read. On the net I found info where it said it's an LA1186. Front end chips are used on FM to boost the signals in front of the main chip that operates the radio.

[NOTE: For those not into radio circuits per se, an IF 'can' or filter helps the radio filter and amplify the radio waves. An IF 'can' is a coil, and a ceramic filter is a solid state device that basically does the same thing, except differently. Generally, IF 'cans' have a wider, more pleasing fidelity, whereas ceramic filters are a bit more sharply tuned, and a lot of radio aficionados like to put ceramic filters in their radios to make them pick stations apart better.]

The audio chip is relatively quiet compared to the GE's audio circuit (the Optimus's AF audio chip is a UPC1213).  UPC1213 AF audio chips are rated at anywhere from 1.8 to 2.4 Watts -- which obviously depends on the volts supplied to the chip, and the impedance of the speaker. The clearest guess I have on the UPC1213's output here is that it's putting out 1.3 Watts max (9V, 8 ohms = 1.3W according to the UPC1213 datasheet), because the Optimus has an 8 ohm speaker.

Using three separate chips for the RF, IF, FM and AF functions is different from a GE Superadio, which uses discrete transistors for the FM RF section, a single standard, bipolar junction transistor for the MW/AM RF amp, and a single chip for FM-AM IF and AF.

A pic of the antenna terminals of the Optimus "super radio". The far left terminal is for the AM band. The next connections to the right of it are for FM and Ground, with choices for 300 ohm and 75 ohm FM antenna connections.

The Wide/Narrow switch on the Optimus is for MW/AM only, and it narrows the bandwidth a little bit for DXing. When it is set to wide, it's not as drastic a difference as one encounters with a GE Superadio III, which also has a Wide/Narrow switch.

In some cases, having the Optimus set to 'WIDE' on AM improves the performance and the sensitivity, which is the exact opposite of how it works with a GE Superadio. This is something I discovered by accident after I first wrote this article. So if you have an Optimus and you're running it on "NORMAL" (Narrow filtering), try the 'WIDE' setting.

The Optimus's AF Audio chip, as I said, isn't as loud as a boombox or a GE Superadio -- even though the speaker will handle 8 watts, I think the AF chip is putting out less than a watt. It still gets the job done. The speaker -- a 4 inch one, smaller than a GE Superadio's -- is a good one, and the headphone jack is mono -- so a stereo-to-mono adapter is needed when using stereo headphones.

A pic of the Optimus 12-603's 8 Watt, 8 Ohm speaker, which is capable of handling anything the radio's 1-2 watt AF audio chip can put out.

Overall, the sound is very good on an Optimus, even on the MW/AM band. FM and AM are both rich sounding, and crisp and clear, with the tone controls truly tailoring the sound where desired. The bass cranks audibly, and the treble control can either sweeten the sound or dull the highs where desired. The radio is more crisp sounding and less 'scooped' sounding than a GE Superadio.

One curiosity is the main PCB -- at the top of it, it says "Super Radio" and "City 110396". I am guessing "City" might have been the name of the manufacturer, and "Super Radio" obviously indicated what Radio Shack was trying to emulate with the Optimus.

A pic of the 130mm MW/AM loopstick -- the same size loopstick used in the Realistic TRF 12-656, an earlier Radio Shack TRF model produced 1978-1979 or so.

DX PERFORMANCE -- GOOD, BUT LESS THAN A GE SUPERADIO

Long distance MW/AM band listening on the Optimus is quite good. It's not up to a GE Superadio, but better than a lot of other radios, as it's a TRF.

For example, while typing this, I am listening to KSTP 1500, with clear reception (minor splash from 1510 KGA's hip-hop music just one channel up). Usually KSTP is one of my test stations. If a radio can pull it in from nearly 1400 miles away (2200 km), it's a good radio.

The clarity of sound helps in DXing, as the radio sounds good through its speaker. On DX channels I find I have to turn the volume up over half (sometimes to 3/4 or more) to get a decent read on the station. My other test station is 1570 XERF, a bit farther away at 1700 miles (2730 km). Right now it's barely readable on my Sangean PR-D5, and the Optimus only receives traces of audio on peaks, with some bleedover from 1560 KNZR Bakersfield. XERF comes in (unreadable, but audibly in staticky Spanish) when I add an external loop.

I also heard KXEL Waterloo, Iowa on 1540 Khz, underneath local station KXPA (which plays standards and an eclectic mix of classic hits at night) in its weak spot.

Tonight on the X-band, the Optimus just picks up XEPE 1700 (Mexican Spanish talk) without an external loop. With the loop, it comes in readably, along with a music station just behind it. It's weaker than it should be otherwise, though, as my PR-D5 picks up XEPE, plus two stations behind, just using its 200mm internal antenna.

Also, recently, I have logged KMRI 1550 "La Raza" (in Salt Lake City, Utah) with Ranchero music, and KMPC 1540 Los Angeles with Korean programming -- even without a loop.

An external loop is probably a must for serious Long Distance listening on an Optimus, although below 1600 the Optimus does well on its own. If you use an external loop, the Optimus favors the right side of the radio, or a 'sweet spot' right in front of the '108' on the FM dial (probably where the loopstick's coil is).

A 130mm MW/AM ANTENNA, AND EXTERNAL TERMINALS

I also measured the antenna on the Optimus. It's about 130mm, which is similar to the one the DX-375 has (140mm), and several other good radios, including one of its predecessors (the Realistic TRF 12-656) -- and bigger than some radios like the Sangean ATS-505, 818, etc. (which have 100mm loopsticks).

The Optimus, like the GE Superadio it emulates, also has antenna terminals on the back of it -- for MW/AM and FM. I don't know anyone who has ever used rear terminals with a GE or Optimus radio, but it's nice that they are there, in case one wants to use an outdoor antenna, or beverage antenna on a DXpedition.

Even so, when using the external antenna terminals on the AM band, I would use some sort of diode protection to guard the radio against static discharge -- as the RF amp transistor is an FET, and FET transistors are sensitive to static and can blow if a static discharge hits them, and the 12-603 doesn't seem to have diode protection on the external antenna terminal. The FM antenna terminal seems to have back to back diodes. According to the only schematic I could find, they don't show up on it, but they're clearly visible on the main PCB. AM external antenna diodes, however -- at least from a cursory look at the radio -- appear to be missing.

A couple back to back diodes from the AM terminal to the GND terminal would do the trick (two diodes, wired in parallel, each diode in opposite polarity from the other). They could be secured externally, just screwing them in back to back between the AM terminal and the GND externally. In a pinch, a high value resistor (like 500 ohms or 1 megaohm) might also work to bleed off static electricity if you use an outdoor wire antenna with an Optimus.

BATTERY LIFE AND EMERGENCY PREPAREDNESS

I don't know about battery life in an Optimus -- it's been so long since I had batteries in mine I don't know how long they last. My guess is that with the lower audio output, battery life is probably very good for the size of the radio. It probably would be a good emergency radio for that reason.

If you are using batteries in your Optimus -- should you have one of these radios, or find one -- don't forget to use the AC/DC switch on the back of the radio! It's easy to miss!

A pic of my Optimus 12-603 before I removed the tiny patch of rust forming on the upper left side of the grille. Such things can happen if a radio with a metal grille is sitting near a kitchen window or refrigerator for a long time -- especially in a humid climate. I cleaned it with a small knife file (sandpaper might have taken off too much paint around the rust) and treated it with spray lubricant, which I spray on a paper towel and apply that way. Once you do this, you have to continue to treat the rust affected area to keep it from getting worse. If black paint is removed, a black Sharpie perma-pen can recolor it. You may have to retouch it with a black Sharpie later on, but it's no big deal. I've done the same to one of my GE SR3's and the grille of my Panasonic RF-B45. Spray lubricant will check the growth of rust. But the grille has to be rechecked periodically, and maintained.

AS '90's AS IT GETS

In conclusion, if you happen to have one of these Superadio clones, or see one for a reasonable price on the internet, they're worth the money. The all-black radio style is about as 90's as it gets, for one. The overall good performance is another plus. The main drawback is the MW X-Band. Even using an external loop the X-band is a bit weaker than a GE Superadio or Sangean PR-D5. During the 1990's AM radio technology for tuning consumer radios 1600 to 1700 wasn't as proficient as it is presently. I have a 1996-era Sony Walkman M78 that tunes from 520 to 1700, and it's basically dead above 1600, and it's digital. Then again, I might have an Optimus that wasn't aligned as well from the factory.

For anyone who has one of these radios, and would like more info, Mr. Carter's excellent Superadio web site has a page dedicated to the 12-603, with in depth info on the radio:
http://earmark.net/gesr/12-603.htm

IN OTHER LIFE...

In other, non-radio related things, the weather here has taken a turn for the rainy. It's still fairly warm here in the Seattle area, with daytime temperatures in the 70's F (about 18C or so) and nights reaching 50F or so. This weekend is our Labor Day weekend, which used to be a holiday observing the rights of workers and the like, but now is merely a three-day weekend for people who can afford it to go to the ocean or mountains. I, of course, am staying home.

As I type this, I am in my writing room, and the South Asian music of 1600 KVRI (a station about 100 miles north of here) is playing on both my Sangean PR-D5 and my Optimus 12-603. The PR-D5 obviously has the station in a bit better (with it's 200mm loopstick and DSP chip), but the main difference is the fadeouts. A little more cleanup on the Optimus (I found a very small patch of rust starting on the edge of the grille) and I'll be taking pictures to put on this blog post.

Snow in March, 2019. When the lights were out... but was it beautiful outside.

As today's extra pic, I'm including a snow pic from earlier this year. I mentioned in March that we'd had a snowstorm, but I never included any snow pics. Here is one of some fir trees, with a hill in the background that has more snowy trees. When I was a kid, snow on fir trees seemed so magical. It not only reminded me of Christmas, but because snow is rare here, it always struck me as a Christmas card come to life.

Until next time, here's hoping that life is going well wherever you are.
C.C. 8-30-2019

ADDENDUM, 1-16-2021:

After about a month or so of not using my Optimus I switched it on to hear it playing while doing some blog writing, and when I tuned towards the middle of the dial -- towards a MW radio station I wanted to hear -- the radio acted wonky, as if it didn't want to stay tuned on the station... the tuner pot was wigging from just sitting. Oxidation. 

What I did was to tune across the entire MW band a couple times at slow to moderate speed, and it fixed the glitching. It may need more Deoxit tuner lube/cleaner, but I didn't want to take the radio apart at the time, to do that. 

When radios use potentiometers and varactors in the tuning circuit, that can probably be an issue -- oxidation inside the tuner potentiometer. I've never had this issue with my GE SR3, and Optimus Superadios are supposed to have been supplied with high quality tuner components, so I'm just chalking it up to oxidation (from a long period of disuse) for now, probably left over from sitting on top of the refrigerator for years, and I probably didn't get all the oxidation out of the tuner when I gave it a shot of lube last time.

Caveat: if you own one of these 90's marvels, turn it on, tune around, give the radio some exercise now and then. :-)

ADDENDUM, 9-19-2022:

Two nights ago I decided to fire up my Optimus 12-603, after another year of non-use. The same thing happened. The tuning and reception in the middle of the AM band was wiggy until I tuned back and forth, across the dial, several times. Obviously, some dust or oxidation occurred, and tuner potentiometers are fairly sensitive. 

Now the radio is working normally. I guess it's time to give the tuning potentiometer a shot of DeOxit. Or use the radio more often -- which is probably preferable. Since then I've been using the Optimus every night for a bit.

As it was, the night I first fired the Optimus up I was able to hear WCKY, Cincinnati, underneath KFBK Sacramento. WCKY is about 2000+ miles East of here. Which isn't bad for a radio just using its internal antenna! The reception was remarkably clear, also.

I also added a little to one of the captions in this article, where said that I apply spray lubricant to bits of radio grille, from which I have removed rust (using a small needle file). I apply the spray lubricant to the grille with a paper towel -- spraying the paper towel, and then I wipe the lubricant on the grille section that way.

ADDENDUM, 10-14-2024:

I recently learned that the Optimus 12-603 seems to be more sensitive and DX'es better with the radio's filter switch set to 'WIDE' instead of 'NORMAL' (i.e. Narrow) as you would normally have a GE Superadio set to for DXing. So I added a paragraph in the article to reflect this. The conclusion is to switch back and forth, depending on MW DX conditions. In some cases at least, WIDE will work better than "NORMAL".

I also added a sentence on the using 'back to back' diodes on AM, when using an external wire antenna, which could protect the RF amp transistor against static electricity, as well as a sentence suggesting that Optimus (and GE Superadio 3) owners move the tuner back and forth from 520 to 1700 a couple times before using the radio, if it's been sitting unused for several months (to clear any oxidation from the tuner varactor potentiometor -- which is similar to a volume control).