Hy-Gain 623 (Utopia)



Classic Status: Hybrid premium, 23 channel SSB Base

Appeal: Previously owned one, and also owned by friends.

Condition: Cosmetic, Good. Electrical, Good

Acquired: Late 90's, from Blue Bandit

This is my trusty Hy-Gain 623, also known as the "Utopia".  This model was first made in 1974.  The 623 was somewhat of an oddity in the CB radio market in the 1970's.  There were no other radios which shared it's unique hybrid circuitry and design, in sharp contrast to so many other "cookie-cutter" rigs that were being made back then.  This rig was also a study in contrasting technology, as part of its unique circuitry included a state-of-the-art 1st generation discrete chip Phase Locked Loop (PLL) digital frequency synthesizer,  while at the same time utilizing an "old school" tube R.F. output final amp.  The audio amp is a unique (for a CB radio) direct coupled solid state design which yields fantastic sounding transmit audio which rivals a full tube rig in warmth.  The receiver is a simple single conversion design, but it pipes both the AM and SSB I.F. through a high quality narrow 7.8 Mhz crystal filter which results in a fairly sharp and narrow bandwidth with very good adjacent channel performance.  The R.F. front end consists of F.E.T. type transistors which have many of the characteristics of tubes, including R.F. overload immunity.  The clarifier control could be expanded to cover, not just one, but many channels and this was a common method for gaining access to the RC ("A") channels and for going below Channel 1, for those inclined to do so.  The "S" meter is one of the best that I have ever seen on a CB rig.  Not only is it large and easy to read, but it tracks fairly linearly.  Calibrating the meter for S9 at 50 uV, you can then decrease the signal in 6 db increments and the meter will drop in 1 "S" unit steps all the way down to S4 before it starts to lose its linearity. The same is true going above S9 up until +30.  The transmitter side of the meter accurately tracks in actual watts as well.  Nice!  It would seem that whoever designed this rig paid a great deal of attention to details, and it really shows when operating.  

Despite their fairly high cost (Only the Tram D201 and Browning Golden Eagle were more expensive at the time), there were a few 623's in my local area.  Those who ran them had plenty of good comments to make regarding the performance of the rig.  Interactions with these people eventually resulted in me finally getting one second hand for a reasonable price in the late 70's, after 40 channel rigs became legal and the value of the old 23's plummeted.  I used the rig for a couple of years, alongside other rigs.  When I was forced to cut back on my growing stable of radios a few years later, I foolishly sold the rig.  When I started waxing nostalgic in the late 1990's about some of the "classics" of the day, it came as no surprise that I would desire another 623.  Eventually I got my wish.

Now for a little background history on my current rig.  My second 623 came my way courtesy of Blue Bandit sometime in the mid 90's, after he had picked it up from another local and having served as his vacation home base radio for several years prior.  It was not in A-1 pristine shape, and it took a bit of work to get it back to good operating condition.  Somewhere along the line, a previous owner had changed the microphone jack from the original 1/4 phone jack, to a more common 4 pin style.  The rig needed to be completely cleaned both inside and out to remove cigarette tar film. The film coating had gotten so bad, that the radio was starting to have frequency drift problems as a result.  Some of the solder connections on the plugs and sockets needed to be touched up.  A few filter caps were changed out, and the varactor tuning diodes in the VCO circuit were changed to higher range versions to accommodate channel expansion mods, which were performed so that I could use the radio on my then home channel of 29.  All of the controls and trimmer pots were either cleaned or replaced. The volume control had also developed a problem where it will not turn all the way down, which required replacement.  Considering that the radio is now over 35 years old, I guess this sort of stuff is to be expected.  The SSB and AM power mods were removed and the rig was given a complete alignment.  So that's where the rig now stands.  

Now for the post alignment performance specs (My own measurements, not the manufacturer's claims):


Sensitivity: .3uV (.2uV SSB)  for 10db S+N/N. 

Adjacent channel selectivity: 60db @ 10Khz.

I.F. Frequency: 7.8 Mhz.


AM Power: 3 watts.

SSB Power: 16 watts.

AM Modulation: 120+%, 15 watts peak (No modulation limiter was included in this design).

2nd Harmonic suppression: -62dbc.

Other spurious emissions: -55dbc.


Now, the numbers are rather dry, and only tell a part of the story.  How the rig performs in actual conditions is a better indication, and the following is my subjective opinion of the rig.

This rig, I have to admit, is one of my favorites.  Both the receiver and the transmitter are first class.  But the main reason I choose to run this radio above some of my others is that I have a unique interference problem in my radio room.  I have a cable modem and wireless router which radiate all sorts of spurious signals.  Some of these spurs fall into the image frequency of some radios equipped with a 455Khz I.F.,  which causes a steady S5 noise level while the network equipment is on.  One of the network's bigger spurs is at 27.220 Mhz, which can reach a level as high as S9 on the meter.  The Hy-Gain, since it does not use a 455 Khz I.F., is immune to much of this interference, and the narrow bandwidth, and sharp skirts of the crystal filter puts the 27.220 Mhz spur completely out of the receiver pass band.  Because of this, I can hear people much better on this rig than on some of my others.  Because of the narrow I.F. bandwidth, I can also instantly tell if another station is off-frequency.  Someone as little as 1 Khz off is clearly noticeable, and anyone more than 2 Khz off sounds like they are transmitting on SSB. The receiver audio fidelity is fair, but not outstanding.  I mostly attribute this to the condition of the internal speaker, which is still the original 30+ year old part, which is also sporting a small hole in the cone.  The transmit side of the equation is similarly impressive with that of the receiver.  Most people like the "warmth" of the modulation from the Hy-Gain.  It compares favorably with my Tram D201 in both punch and clarity.  Lack of modulation limiting allows this rig to "let it all hang out" without being clipped to 100%, but you have to be careful not to drive the audio too hard or the audio amp goes into a curious shutdown mode, where the amp just stops amplifying and it takes 1 or two seconds for it to recover.  This is a curious design quirk that all 623's that I've seen have exhibited.  It's normally not a problem for those who are conservative in their mic level setting.  But for the "nothing short of maximum" crowd, this could pose a problem.  Another quirk that I observed, relates to receiver performance.  I noticed that some of the weaker stations had what sounded like a heterodyning signal riding along with their signal.  It's not strong, but it noticeably, if only slightly, distorts their signal.  When the problem didn't go away after a few nights, I started looking into it.  What I found was that on channel 21 (Where I do 98% of my talking), there is some sort of synthesizer mixer spur that combines with the demodulated signal, and causes this condition.  Other channels do not do this, and if I drop to channel 20 and use the clarifier to slide up to 21, the problem is gone as well.  I don't know if this is a design issue, or a problem caused by the well used condition of my 30 year old rig.  Since I can workaround the problem, it's not a something which affects me all that much, except for the psychological effect of knowing that there is something "not quite right" in the rig.

What attracts me most to this rig is the overall receiver performance in the face of my local interference issues as well as the accuracy and size of the "S" meter.  I am also pleased with the nearly "Broadcast radio" sound of the transmit audio.  The overall professional-looking, no-nonsense appearance of the radio is appealing to a utilitarian like myself.  If I were to come up with any negative points, I would have to cite the aforementioned synthesizer quirk, as well as a tendency for the frequency alignment points to drift over time.  Right now it is a neck-n-neck race between this rig and the Tram D201 for my vote as overall favorite.