GR1225 Is It Really 100% Duty at 25 Watts?

[Birken Vogt]

We have a VHF 1225 repeater on the shelf getting ready to go into service as a repeater. It would be nice for us if it could do continuous duty at 25w but I want to know if it will burn up if we try this. Another user in the vault has his UHF untis set up on their sides with little computer fans blowing across the heat sinks. I don't know what power level they are running or if this is really necessary so that is why I am asking you guys. (When it all comes down it will not run 100% for a long time in the future but it might run for some minutes during a yak-fest now.) The radio just looks so small to be continuous.

[Bill_G]

That series is *not* continuous duty xmit. It will run cooler and last longer at 25W, but you can still burn it down by talking too long.

[wavetar]

It's true, despite the Motorola claims, the GR1225 won't last at 100% duty cycle even at 25 watts. However, the majority of the time, it's the solder on the final PA transistor that dries out from the constant heat & gives up, not the transistor itself...it's likely rated for 100% duty at that power level. If you remove all the existing solder & reflow with high temp silver solder, it will last much longer. An extra fan across the heatsink, and you'll be in business for quite some time.

[KX5MOT]

I have a 10 watt UHF version, just curious how well they last?

[Will]

The big problem with the GR1225 is getting enough air blowing past the heatsink. The GR housing is not really made with air flow in mind.

The R1225 repeaters we have have just the R1225 radio vertically mounted with the heatsink up and the front down AND a fan blowing across the heatsink on a flat rack panel. In this configuration the hot air rises away from the heatsink. Takes up more space tho. But there is no controls or other stuff in the way power supply is on the other side of the rack panel with the duplexer.

Look into the better German fans at frozencpu.com.

[Will]

I have a 10 watt UHF version, just curious how well they last?

The 10-12 watt do much better as there is less heat dissipated in the heatsink. Also the heatsink is smaller, no extended fins like the 45 watt versions.