Gemtronics GTX-77

[scooter490]

I have A Gemtronics GTX 77 40 channel sideband mobile radio. It has the PLL02A loop in it ,but when I did the channel mod it will not go. I was told it needs a crystal swap to make the loop go. It's a good radio with and slides 5KC up and 4 down. I know the old O2A loop will go. I have a AM only GE that has the extras in it. I can't seem to find any information on the radio. It looks a lot like a Colt 480.

[TheCBDoctor]

I have A Gemtronics GTX 77 40 channel sideband mobile radio. It has the PLL02A loop in it ,but when I did the channel mod it will not go. I was told it needs a crystal swap to make the loop go. It's a good radio with and slides 5KC up and 4 down. I know the old O2A loop will go. I have a AM only GE that has the extras in it. I can't seem to find any information on the radio. It looks a lot like a Colt 480.

Hi scooter490,

You do not need to replace any crystals in the Gemtronics GTX77 for channels. The 02A chassis is the most versatile PLL ever made. Sams Photo Facts made a service manual for that radio, which I have. CB-224.

Gemtronics is actually a great radio made by Cybernet. The base stations had covers made of real wood.

Respectfully,

[scooter490]

I can't seem to get it to go above 40.

[Night Crawler]

Check your work it should go above 40 if done correctly unless the chip is defective.
[Please login or register to view this link]

[TheCBDoctor]

I can't seem to get it to go above 40.

I would be careful because the 02A PLL is no longer made. You have to cut the traces going to the binary counter, and then put 4.7 K Ohm resistors across the cut. Unlike the MB-8719 the 02A does not pull high when left at rest. If you put voltage to a Pin that is normally low it will pop the PLL. You need to use resistors across the cuts you make. Many mods call for 4,700 Ohms, but I use to use 6,800 Ohm resistors. It will still work and reduces current draw.

Be careful and good luck.

[scooter490]

Thanks guys. The only combo I didn't try was pin 10 to ground. I have the 3.3k resistors on the cuts. I have the Sam's photo facts coming for the radio, so I'll be able to find a ground then.

[Nagant]

Your Gemtronics GTX-77 is what I would consider a rarer Cybernet radio and somewhat collectible if it is in really nice condition, especially since it's a SSB. However doing the channel mod lowers the value a fair bit.

[scooter490]

I do have uppers in the radio now, but it only goes to 59. Channel 1 becomes 28 and it goes up to 27 which is 59. At 28 it's back to 28 again. To get that combo I cut pin ten added a 3.3 K resistor across the cut, then put a wire on pin 10 and another to board ground Via a switch. I've seen information that says to do the same to pin 9 to get from 60 on up to 28085,but that does not work. So now I'm lost.
Any idea's?