"Floyd Sense" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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I'm just about there with my TR7 restoration, but have one more elusive
problem. I've got the later pre-driver board with the MRF476. After
running CW for a while at 100W out, the output drops off and eventually
goes
to about zero. If I let it sit for a while, everything is OK again. I
traced the problem to the MRF476 - when it happens the heatsink is very
hot.
If I cool it down with a blast of cooling spray, I have full output again
until it gets hot. I found the problem described pretty well in the
document by VE3EFJ titled: "Drake Mods, TR7 Mods". His solution is to
improve the bias on the transistor by inserting a bundle of three
paralleled
1.8 ohm 1/8 watt resistors.
I read somewhere else that one shouldn't use this approach. Has anyone
else
had this problem and fixed it with the suggested bias change? I really
don't see any other option at this point. I've touched up the solder
joints
on everything in the bias network for that transistor and no change in
behavior.
73, Floyd - K8AC
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