gr1225 power amp question

[cms1126]

Ok so after reading all of the wowes about the gr1225's pa going out i have come to the conclusion that that is the problem with my vhf gr1225. my question is, would it be possible to use a gm300 or m120 or maxtrac 300 pa on the 1225? and if not does anyone know of any places to get refurbished pa's or used ones that are in good condt? i dont really want to drop $300 on a new one.

-Conner

[Bill_G]

If you have no power out on xmit, but can hear the station on a portable or a service monitor, chances are the rfpa died. Theoretically yes, you can swap the boards between models in the heat sinks. Pay attention to the connectors. You have to do an alignment afterwards. Sometimes you can recover the rfpa by reflowing the mica caps with silver solder after removing the burnt solder.

[JimCT]

The most common problem with GR1225 PA's is the chip capacitors on the base and/or collector tabs of the output transistor. If they're bad, you can sort of pick them out with a probe. Sometimes it's possible to resolder them, but they won't last. They're not terribly expensive. They should be soldered with solder containing 2 percent silver. It's a little hard to find, but worth the effort as the caps will last much longer.

[Will]

Some R1225 25 - 40 watt power amplifiers have the short heatsink.
The longer heatsink does better but still needs lots of wind going by it.

Resolder with silver bearing solder at the final transistor, replace some of the chip caps with clamped book mica types.

[chartofmaryland]

I have more 1225 UHF and VHF pa's than I can imagine, these were heading for the circular file when I pulled them from its cold dead hand.

There is great reward in replacing all of the capacitors around the final and on the underside of the PCB so the spurious output is corrected caused by overheating the PA, along with providing a stable PA once repaired and the power adjusted.

All, and I mean ALL 1225 PA's have to be run at no more than 25 watts.

If you attempt to produce more than 25 watts you have to provide an external heat dissapation system that is liquid cooled or go ahead and get another PA to replace the failed unit as you will be replacing it soon.

The only time it worked for me to run the 1225 PA at 35 watts for an extended period of time was to remove the radio chassis from the repeater enclosure and place it into a server rack in a server room where the room temperature did not exceed 68 degrees.

I have large quantities of the replacement parts and have changed many of the failed units with all coming back online and providing service when the power was reduced.

CoM