This is my opinion so take it for what it is worth.
The Radios like the 6900FFC4 ( and the large Galaxy) are handicapped from the start as far as being stable on SSB.
You have a radio that is "fairly stable" on SSB and then you bolt a 400 watt amp to the chassis.
Almost any radio needs to be turned on for a bit before it settles down on frequency, you have to give the radio a moment for everything in the radio to warm up .
As you start talking, you are pouring heat into the chassis of the radio, 4 2879`s ( or in the case of the Galaxy 8 MOSFETS) and it builds fast, then the internal fan comes on. Then you un-key and the radio starts dropping temp and you are getting Temp swings.
I know that the heat sink on these radios have fans, but look at the size of a heat sink on a DX-500 and the heat sink on the bottom of a 6900FFC4.
And even the 500 needs a fan(s).
Some will say that the heat sink is not getting that hot...but a considerable amount is getting transferred to the side rails of the radio, and it is heating the internal components.
The VCO section of the radio has to deal with this and I just feel it is too much.
If you have an AM/FM only radio it is not so critical, but in a SSB radio it is just asking too much.
Plus the added heat is not good on the longevity of the radio in general.
I feel you are better off with separate radio/amp combinations, and the added thing that some one already said, if the amp goes down, you can still talk on the radio.
For what it is worth.
73
Jeff
