The Cobra 148 GTL-DX Transceiver was manufactured in Taiwan (Former Rebublic Of China - R.O.C) for Cobra Communications Product Group, DYNASCAN CORPORATION, 6460 W. Cortland Street, Chicago, Illinois 60635, USA in the late 1970's and early 1980's.
Cobra made several versions of the 148 GTL-DX Transceiver and Cobraworxshopz aim to highlight the different chassis and revisions to ease identification of this now Classic and in our opinion Number #1 CB Transceiver of all time.
The First Cobra 148 GTL-DX manufactured was the MK1 Chassis PC - 879 AA/AB
Shown below is the Chassis number and location inside the MK1
After the success of the MK1 Cobra released the MK2 Chassis PB - 010 AA/AB
The MK2 Chassis had several circuit improvements over the MK1 and less components.
Shown below are the Chassis numbers and their location on the MK2 Chassis.
The Cobra 148 GTL-DX MK1 has several external visible differences from the later MK2 making identification easier without the need of removing the Cases. The Bezel and Face Plate of a MK1 and MK2 are virtually the same but the rear panel has all the clues as to which version you own...
Cobra 148 GTL-DX MK1 serial numbers, stamped into an aluminium plate and riveted to the rear panel of the Transceiver, generally start with the number "03" see the MK1 serial number plate below "03001555". Cobraworxshopz are interested in finding the MK1 with serial number "03003349" do you own this??
Cobra 148 GTL-DX MK2 serial numbers, stamped into an aluminium plate and riveted to the rear panel of the Transceiver, generally start with the number "13" see the MK2 serial number plate below "13005330". Cobraworxshopz are interested in finding the MK2 with serial number "13011251" do you own this??
Cobra 148 GTL-DX's that have a Heatsink attached to the rear panel, generally loose the serial number plate to accomodate the Heatsink. When doing this mod, some Technicians remove the "Bias-Shorting" PCB from the RF output stage and replace it with the serial number plate, thus keeping the identity of the Transceiver, see below.
Further differences between a MK1 and MK2 Cobra 148 GTL-DX can be clearly seen on the rear panel of the Transceiver.
On a Cobra 148 GTL-DX MK1 the RF driver and RF final Transistor are side-by-side, screwed to the rear panel of the Transceiver. The screw heads can be clearly seen above the serial number plate on the rear panel. On the MK1 only One (1) hole is visible between the RF Transistor screw heads drilled into the rear panel. See the inside picture below, showing the hole (arrowed) between the RF Transistors.
The Cobra 148 GTL-DX MK2 RF Transistors are spaced much further apart on the rear panel, with 3 (Three) holes visable between the RF Transistors Screw heads, see below picture.
Cobra 148 GTL-DX MK2 back panel showing Three (3) holes arrowed in Green between the RF Transistor screw heads arrowed in Blue, see below. (notice original plastic cover still on serial number plate - one of our Mint 148's!)
A quick glance at the rear panel of a Cobra 148 GTL-DX should give you enough information as to which version of 148 MK1 or MK2 you own or are considering buying, even if the serial number plate is missing.
Another notible difference between the MK1 and MK2 is seen on the rear panel. The MK2 has two (2) Oval shaped holes punched into the Aluminium that the MK1 does not have. See the below MK1 rear panel for reference and compare to the MK2 underneath.
MK2 rear panel shown below, the two (2) Oval holes are arrowed in Green
For a definitive answer a look inside the Transceiver at the Chassis number of the PCB (Printed Circuit Board) is essential.
If you are having difficulty identifying the version of Cobra 148 GTL-DX because the serial number plate is missing or a Heatsink has been added and the serial number plate has been thrown away and not used as the "Bias-Shorting" PCB (shown earlier) then here are some differences to look for.
The Cobra 148 GTL-DX PC-879AA/ABMK1 Chassis uses 4 rows of tuning coils/inductors with 4 Crystals (MK1 has 5 Crystals in total including PLL Xtal). The below picture shows the 4 rows of coils/inductors and associated Crystal at the end of each line, arrowed in Red.
The Cobra 148 GTL-DX PB-010AA/AB MK2 Chassis is very different when compared to the MK1's same Tuning coils/inductors. The MK2 has only 2 rows of coils/inductors and 2 matching Crystals (3 Crystals in total including PLL). This later and more advanced design makes the MK2 simpler to re-align and tune for Technicians and for the Manufacturer during production and uses less components.
There are many circuit and component differences between the Cobra 148 GTL-DX MK1 and MK2 Chassis. Cobraworxshopz have highlighted just some of the easier to see variations between the MK1 and MK2. Identification of this excellent Transceiver's different Chassis should hopefully be made easier with this information.
PB-010 AA & AB
The PB-010AA Chassis was the First Cobra 148 GTL-DX MK2 version produced. There are a few notible differences between the AA and AB Chassis. The below picture is of a 010AA Chassis, notice how the 3 tuning pots VR3, VR4 & VR6 are all orientated the same way round.
The below picture is of a 010AB Chassis tuning pots VR3, VR4 & VR6, notice how the middle tuning pot VR3 is upside-down compared to the 010AA Chassis above. (VR3 slightly obscured by black wire).
Another Interesting difference between the 010AA and 010AB Chassis is the fact that some of the Transistors on the 010AA Chassis are assembled on the PCB 'Backwards'. Compared to how they are shown on the 010AA PCB printed layout and on the 010AB PCB. The picture below shows an 010AA Chassis, notice how TR39 (centre) and TR14 (top left) are shown as being assembled the wrong way round, like some other 010AA Transistors!
The 010AB pictured below shows TR39 and TR14 in the correct way round compared to the 010AA above.
Further differences between the 010AA and 010AB Chassis can be seen in the Crystal Filter FL3 (10.695Mhz) used in the two revisions of Chassis. Pictured below is the 010AA Crystal Filter (MCF Model 10M-4S Taiwan Uni).
The 010AB Chassis uses a (TEW FL096) as FL3 10.695Mhz Crystal Filter, shown below.
The PB-010AB MK2 was the latest Chassis but sadly the last Cobra 148 GTL-DX Chassis produced (Except 148F GTL-DX in 1997). A pinacle of RF Engineering and in over 30 Years since it's design the PB-010AB Chassis is still being copied and produced today, Superstar 3900/158EDX/3900EFT, Connex 4800, Magnum Deltaforce, S-9, Ranger 2950DX to name just a few that share the same 010 PCB Chassis design.
The below picture shows the solder-side of a MK1 (PB-879AB) Cobra 148 GTL-DX Notice the extra components that have been added to the chassis.
The below picture shows the solder-side of a MK2 (PB-010AB) Cobra 148 GTL-DX Notice how the later chassis negated the need for extra components to be added when compaired to the MK1 chassis above.
The "13" Connection
The Cobra 148 GTL-DX and the number "13" seem inexplicably linked for some reason? Cobraworxshopz have over the years discovered "13" connections with the number "13" and the Cobra 148 GTL-DX Transceiver.
Here are a few we will share with you, how many can you find? Please email us with your Cobra 148 GTL-DX number 13 connections and we will publish them here;
The MK2 serial number starts with, you guessed it, "13"
The front panel of a Cobra 148 GTL-DX has "13" controls, as mentioned in "Section IV" of the original Cobra 148GTL-DX owners manual, see below.
The model number Cobra 148 GTL-DX interestingly, 1 + 4 + 8 = "13"
There are more, can you find them? Some are not as obvious as the aforementioned.
You may know of some we don't so please let us know your findings.
Boxed as supplied New
John "JENTEC" Nugent, the late Genius and maker of the famous Cobra Transceiver MKV also made a "special" Cobra 148 GTL-DX. This "special" JENTEC Cobra 148 GTL-DX was the forerunner to the Transceiver MKV. The radio was easily recognisable, sporting a black/charcoal JENTEC Cobra 148 GTL-DX Face Plate with white lettering, making it is easy to see where the MKV has it's origins. John designed a modification to expand the frequency PLL (phased locked loop) coverage by utillising an EPROM type device or Electronically Programmable Read Only Memory.
The JENTEC 148 modification was called the "COB P1" dated 15th December 1983.
The mod consists of 3 pcb's (printed circuit boards) shown below is the JENTEC COB P1 pcb. Notice the circular clear plastic 'window' in the middle of the chip. Inside the window is the actual I.C. (Integrated Circuit) complete with connecting wires surrounding the chip. The window on the EPROM is designed to allow UV (Ultra Violet) light to bathe the I.C. for a minimum of 30 mins and thus erasing any program data stored. An EPROM UV eraser device is used for this purpose. The EPROM is programmed with binary data in an EPROM programming device connected to a personal computer serial or USB port and then downloaded with binary program code, i.e. 26-30mhz . Once programmed the window must be covered by a sticker for example, to stop the data being destroyed by ambient UV light.
JENTEC COB P1 EPROM Module (1)
The COB P1 EPROM pcb was soldered directly onto the 148 channel selector pcb! via the strip of pins (bottom of picture) Cobraworxshopz have not seen this ingenious design used before or since, the COB P1 circa 1983.
A closer look 'through the round window' of the EPROM I.C. is shown below.
COB P1 Transistor Module (2)
Used in conjunction with the EPROM module are two further pcbs. Shown below is the COB P1 Transistor module, consisting of 4 transistors, 3 diodes and 2 resistors and 5 wires. A hole is drilled through the center of the PB010 chassis through an earth track and the Transistor module is chassis mounted using a plastic space, nut and bolt.
COB P1 Diode module (3)
The COB P1 Diode pcb module is shown below, this is the smallest board that completes the COB P1 modification. Mounted next to the line of tuning pots used for the mode offset frequencies, it utilises 6 diodes and 5 wires, used for band switching, eg. low-low to hi-hi 6 blocks of 40 channels from band switch.
The COB P1 modification by John Nugent enabled his "special" JENTEC Cobra 148 GTL-DX's, 6-band (low-low to hi-hi) capability combined with all the ALPHA +10Khz channels and UK27/81 - UK40FM 27.60125-27.99125Mhz.
Cobraworxshopz wishes to extend our gratitude to Mr. John Godding of Cumbria UK, for his time, effort and assistance with the JENTEC COB P1 information.
Cobraworxshopz.com offer Servicing, Repairs, Tune-Ups and Clean-Up essentials.