Help needed-148GTL driver bias issues

Got a Spare pic of your Divers Foil side?

I have a hunch...

Diode may not be grounded...or at least not grounded to Foil ground - it could be floating earth chassis - back panel.

Some transistors need even 100mA to work.
Mike

Got it - thanks...


Not to be a bother but where are you "plugging in" the diode?


Remember, the diode needs to be - forward biased.

It's just "odd" to see the mA requirement for the Final in AM go so high so quickly.

Older days, we set it in Grant and 148GTL's for no more than 180mA in AM - about 120mA for Driver in AM mode.
They still heated up like banshees.

When you said you got negative voltages, this was why I posted that "180 ohm" resistor mod.
For some ungodly reason, they took care of Finals by trimming voltage across the transistor from Voltage source to Ground . But they neglected the Driver - and I don't know why - losing the 2166 or the 1306 was easy enough - they never bothered to balance out or at least send the trickle current to ground when at idle.

Heck even the 138 as well as the 146GTL are affected (offended) by this omission, Hr2510's onto the PC-122 and even Grant...

Well, you'd ask why worry about idle current - for the very effect you're having now. NEGATIVE Base lead voltages will damage the Driver

Simply put - for the bias itself wasn't the problem - the ability to BALANCE the Bias to keep the 2166 or the 1306 off or stay stable and drain off the 8VTX (floating) across the diode - that current - was the problem.

Galaxy does this on the RECENT entries for MOSFET designs
,
Gotta love that they think a 100K resistor deserves a Capacitor designation...SIGH - their hearts in the right place...

But Ranger/RCI - New home of Galaxy and Cobra...don't...


I'd put one a 180 ohm or even 220 ohm (note the 330 ohm R182) just to take and DROP some of the voltages so the Driver doesn't kick on, in high-gear forcing the Final into full on. Your 400 mA reference...

If you have one 2166 driver in the Hand, it's worth far more than two in the trash...

Ok once installed now what? Well, you should be able to easily trim the mA between 50 to 70mA on the meter and KNOW you're not pushing the Driver with that much, more like 1/2 less mA depending on the Value of your bleeder resistor - the higher the ohmic value - up to the value of the bias buffer resistor in there - you know you're dividing the mA draw by 1/2 between the two resistors - lower value makes the bleeder resistor take in more current - The Diode will take care of the rest. The 1306/2166 or whatever you use in there - will thank you...

Yo're most Welcome - glad you can use this trick to keep the driver driving "safe"


Only thing I wanted to mention

Dmans said:

The remaining carcasses of 148's that I have (with ugly faceplates and rough cases) may find a new home in the Navaho case/cabinet.

73
David

Click to expand...

You're not alone in this - I have several radios with broken bezels - rought shape that need a little TLC over to work on myself.

So I wish you good luck with your endeavors!

Check! Check!

Dmans said:

So I have accumulated 3 or 8 148GTL's in the last couple of years. One of which will be repaired due to the cosmetic condition of the faceplate, case, circuit board etc. using components from the others as needed

Click to expand...

. This is my collection last time I checked, half work—- half doesn’t work, and I’m fixing them when I have nothing to do. Or what else can I do

You can use a galaxy bezel on that radio. Just have to get a face plate sticker because the face plates come off the old bezel pretty hard(usually) Sometimes you get lucky. They have to be straightened. You can get them flat but they will need a sticker to hide the rub marks from straightening.