All Things Wireless & Letterpress

All Things Wireless & Letterpress

Sunday, December 27, 2015

The Lafayette "Dyna-Com", Part Two

My own personal Dyna-Com arsenal is actually quite a recent acquisition.  I have owned several over the years, but usually they fell prey as trade collateral.  Seems the mystique and attraction is rather widespread and somewhat unexpected. So I would buy them.... only to trade them for something else within about a year.  

I always had an attraction to these "Bricks", and purchased my first one in 1977 (I think.)  The reason was pretty surface: Our local Lafayette, in downtown Orlando, FL., carried crystals for what was then called "Channel 22a".  Back before the FCC opened up 40 CB channels, we had 23 channels.  Channel 23 was used on a shared basis with class C remote control devices.  I recall that channel 23 was almost useless in the Philadelphia area when I lived there, because the traffic signals utilised channel 23.  Or, so was the popular opinion behind the mass of tone signals.  Between CB channel 22 and 23 was 20 KHz, or two channel spaces.  These we referred to as "Channel 22a" or "Channel 22b".  These were shorted out on the channel selector of synthesized CB rigs, so they could not be used.  There were countless schemes describing the magic wire to cut to access these "super secret" channels.  It was just too easy to simply buy the high power Walkie Talkie and insert the "super secret" channel crystals!  And so, that's what I did.  Me and the guys (the guys and I . . . sheesh . . ) would hang out on 22a, much the ire of others from whom we wished deliverance from.

Later in years as a Ham, I purchased a couple Dyna-Com 3Bs on this new medium called "eBay".  I used them when I was on my roof working on my 40m vertical antenna, and needed something to both keep me company up on the roof, and provide a way to shout down to the control op when doing remote adjustments at the antenna feed point.  I always got a kick out of working hand-held portables out in the open. And, sorry, it was more entertaining to listen to the CBers than the diminishing crew on 2m.  In fact, I have as of the past five years seen our local amateur VHF community all but vanish.  The CBers are still having their morning coffee on the air.  What gives, guys?

Just as an aside, the longest distance I ever talked point to point on a hand held unit at any time on any band, was using that very Icom 2AT in the photo.  I used it atop Brasstown Bald's ranger station look-out, and raised Thomasville, GA.  Essentially, I was up in north Georgia almost at the Tennessee line, and I talked down to the Florida Line, spanning the whole state of Georgia from north to south, on one watt, two meter FM simplex.  I have also spoken point to point with parachutists at twenty thousand feet in a free-fall drop. Rigs like the Dyna-Coms are fully capable to perform these same amazing point to point contacts, conditions permitting - of course!

So, let's talk about these devices, generally.

These radios were designed to have similar receiving and transmitting characteristics as Lafayette's CB base units, the Comstats 19, 23mk5 and 6,  25A, 25B, the HB series bases and the Telsats.  They have single conversion superhet receivers utilizing ceramic filters.  Adjacent channel rejection was about the same as the big bases and mobile units.  They had a speech amp circuit Lafayette referred to as "Range Boost", which focused increased audio into the amplitude modulation sideband envelopes. I might call it an early form of speech processing.  It was not simply increased gain.  The Comstats had the Range Boost function as well.  It made quite a difference when copying a 3 watt AM signal through heavy QRM.  

They have provision for external mic, external speaker, external antenna, and external power.  Channel switching is a side panel function.  They carry a battery indicator that would indicate both voltage and signal strength . . . to some degree.  On the lower right of the above photo you can just see the external power and charger jacks.

The two and three watt units carried a battery pack for eight AA cells.  The higher power systems used the whole rear panel of the unit as a battery holder for either ten AA cells or twelve equivalent NiCad batteries.  When Alkaline or any non-NiCad batteries were used, a battery spacer was inserted into one row, as seen in the diagram above.  This served the purpose of keeping the voltage to 15 volts (the rated voltage for the five watt Dyna-coms).  The spacer made it possible to use only two batteries in one of the rows.  NiCad batteries were 1.2v each, so twelve NiCads were used.  More on this later.

There were a few accessories available for these units.  Of course, no thinking person who just dumped fifty or more bucks into a walkie talkie in 1969 would just take her naked into the woods.  No, you had to get that genuine cowhide case.  That really dressed her up, and more: they provided genuine protection!  These were cowhide cases that would themselves cost as much as those walkie talkies were we to purchase them today!  Kenwood was the last company to make cases like these, for their TR2400 HTs.  Those were made by Gucci, believe it or not!  The Dyna-com cases, well . . . not Gucci, but I wish my boots were made like these.  Oh, and bringing up boots: you keep these cases supple with saddler's soap and protected them with Kiwi shoe polish.  Just a hint.

Another accessory that was a must is the power supply.  The units rested in it.  Unlike the stand-up chargers for VHF/ UHF rigs, there are no charging connects at the bottom of these units, so you plugged the charger in at the side mounted charging plug.  You plugged external power into the external power jack provided right next to the charging plug.  Two different plug heads.  Lafayette would tell you that you needed their power supply, but any supply 12 - 15 vdc would work for the 5-watt units, for the 1 - 3 watt units,  no more than 13 vdc.  The higher power units would work at 12v, but much below this starves the system.

You could also get an external speaker and an external mic.  For stateside systems that were channelized by individual xtal pairs, which would include all the Dyna-coms up to the 12 channel types, the external mic used a single mono 1/8" mini phone plug.  This enabled you to use what amounted to a small speaker as a carbon mic.  It's the same mic as the speaker-mic used by the walkie talkie itself.  But you still have to key the PTT (push to talk) on the walkie talkie itself.  You could not key the mic.  I found this next to useless.  Not entirely useless, but next to it.  The 23 and 40 channel systems used the standard four-connector mic plugs so you could plug a regular mobile mic and key by it as with a regular mobile or base unit.  The foreign export models such as the Dyna-Com 3F also came with a standard mobile/ base mic plug.  I wish they were used on all the Dyna-coms, but then these foreign models were AM/FM units.  That may have had a bearing on why they did this.  It could have been contracted by the services that intended to use them, such as law enforcement or military.  Dyna-Coms were not used by military or law enforcement in the US, but rather by private citizens or companies, such as construction companies or marine facilities.

There is a drawback to using a keyed mic.  Your body is figured into the design of these walkie talkies.  You, dear user, become the counterpoise for the antenna!  This means that to make your little unit an effective radiating device, your own body, capacitively coupled to the metal body of the walkie talkie by your holding it, provides the ground it needs to see.  How can you tell?  If you have a working Dyna-Com, turn it on, pull out the antenna to full extension (always!  Whenever you use these, pull that 'tenna all the way out!) and set it on a table.  You will hear the S/N, native to the receiver, fall off as you back away.  When you pick it up, those signals become significantly louder.  That's the way almost all such hand held units work!  Of course, with the external antenna (another accessory!) body contact is not necessary.  Mentioning the external antenna jack, let me say that it is also a 1/8" mini-jack.  Great for audio. Not great for RF.  I found that I needed to build a small patch cord converter with an SO 259 at one end to use my external antenna, which uses RG58-U coax for the antenna feed.  My old Sears 1.5 watt CB HT used an RCA jack, which was still inadequate, but not quite SO inadequate in that actual converter plugs were made for several units out there that also used the RCA jack for RF output.  The Johnson "White Face" Messenger One, to name one.  To my knowledge and in my experience, no such adapter was made using the mini plugs.  I may be wrong.  Such a converter plug is not mentioned in the Lafayette catalog....unless I missed it all these years!

There is also a provision for a PA system.  I still can't figure out that one.  Why a PA system from a walkie talkie?  They are not bull-horns.  But . . . I'm sure some one may have used one at a private party or a bingo game, so sure.  Public Address away!  But for crowd control - I'm still trying to form that mental image.

Let's revisit the battery installation for the five-watt units again.

As mentioned earlier, these sets were designed to take NiCads and AA cells.  There is no mention in the manual that there is a slight difference in cell size between the two battery types.  Yet every 5-watt unit I have ever seen will not fit AA cells as shown in the diagram supplied by the manufacture.  Just to make sure, I checked out the AA cells specified that are still being made!

Specifically the Eveready E-91.  The exact same size as the Dura-cell AA batteries.  No bueno! They absolutely do not fit.  Lafayette, what gives??   Let's take a closer look at that spacer deal shown in the manual:

The spacer is a conductive cylinder, like a short metal rod cut to the size of two AA batteries.  It's purpose is to short the negative end of the battery in series above it to the negative terminal of the battery holder section in which the battery "tube" lies.  Yet this only affects one of the three battery "channels" (the troughs wherin lie the batteries when slid into their holding tubes) !  So this spacer reveals nothing.  We are still stuck with two channels that will not hold the specified AA batteries!  So, here are the solutions I came up with.

I simply made three spacers from aluminium rod about the same diameter of  a penlight cell!  One for each channel.  This way I still had 9 batteries, or 13.5 v.  The rods were actually a tad thin, so I built up the thickness by wrapping masking tape around it to build up the diameter so it fit snugly in the home-made "battery tube", which I made by simply taking a sheet of photocopier transparency film, available at any Office Depot or Office Max, and cutting three strips approx three inches wide and long enough to permit the two ends of the battery series within the tube to make contact.

The tubes are held in place with masking tape.  So far, my cheap home-made tubes seem to be doing the trick.  If anyone out there knows of a source for thin walled tubing that will snugly hold penlight batteries in place, let me know, and I will post it.  The purpose of these tubes is to keep the batteries from moving.  Four batteries in tandem can create an avenue for slippage which will, in turn, create a scratching sound through the speaker.  So the batteries and your spacers need to be held in place.  Obviously, the spacers that I made were short enough to make the remaining three batteries in their respective series physically fit!

Now, I did something else that might be...well....maybe not kosher, but it has worked so far.  Noting the voltage being lower than the 15v these sets were designed for, I replaced my spacers with AAA cells!  I then wrapped tape around them to build up their diameters to snug well into their tubes.  So, now we have 1.5v x 12 = 18v!  What th....?   Yes, friends, that's what I did.  And with no apparent issue.  I will need to pull one or two out and place the spacer in two of the channels, but just to show that it can be done, there you are.  I might recommend one AAA cell and two spacers, to be absolutely "kosher" (my Hebrew background popping in there.  Oi!)

Here is a close-up of the battery tubes, the penlight (AA) batteries, and one of the AAA cells in place with masking tape wrapped around it to secure a snug fit.  And again, while I inserted an AAA cell in all three battery tubes, producing a voltage of 18vdc, the current will be different.  Just a head's up.  All this means is that the power discharge from the two different batteries ( I/R drop) will be different.  What this spells is probably a shorter battery life than if all the batteries were the same.  I do not anticipate this to be significant.  But then, we are making do with what we have on hand: parts for these rigs are not made anymore.  So, use your own judgement regarding mixing batteries and cutting and using spacers.

So, that' it for this installment, gang!  Stay tuned for the Great Road Test!

-gary // wd4nka.


  1. Really awesome blog. I have gotten some great Walkie Talkie reviews from here. Thanks for sharing.

  2. Not sure if you are still monitoring this thread, but I have acquired a Dyna-Com 3b from a resale shop. It looks like it was manufactured yesterday! Works great too. It accepts 10 AAs. As it only has the crystals for ch 10, is there any chance of getting more crystals?

  3. Irsno! Thanks for your comments. As you can tell, it does take a while for me to get back to these comments. I promise to check more often. Actually, I am not used to folks making comments at all on my blog! :)

    As far as I can tell at this point, the best way to locate Walkie Talkie xtals, which in my parlance are CB xtals, third overtone, is on eBay. I check to see what it would take to have them made, and wow! Talk about expensive. But on eBay, you can find new old stock xtals for these "Bricks" for between eight to ten dollars a pair (Transmit and Receive xtals.) Make sure the receive xtal is 455 kHz lower in frequency to the transmit xtal. The Dynacoms will handle 26mHz through 29mHz without re-tuning.

  4. Hello Gary.

    I know your problem with Ni-Cd AA batteries.
    He deals with a bit of battery history :-).
    In the past, AA cells were smaller, now manufacturers have used maximum size margins for the cells to have maximum capacities.
    Old devices were not adapted to such great tolerance scales. Old AA Ni-Cd cells were 400 and 450mAh. They were about 1mm shorter.
    Gary, there is a solution when you use AA industrial cells they will all fit properly :-).
    They are shorter, sometimes they need to solder a tiny drop of tin or a thin plate of tin on their poles.

    Charging: According to the 24V power supply, the charging current is reportedly 50mA.
    I have not tested this, currently lack the funds to purchase 12 AA cells.

    Best wishes,
    Arek from Poland.

    ps. I noticed that old 27Mhz portable radios - what the higher power model has less sensitive receiver :-(.
    Lafayette dynacom 3b has a better receiver and despite having 3W input power (1 - 1.5W out) it has a wider range than dynacom 12A.
    Midland portable devices were even worse, fatal sensitivity, particularly powerful models (2 to 5W input power).
    It looks as if the US government limited its reach deliberately, even 5W input power, portable radio had the same range as much weaker :-(