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Icom IC-706MKIIG

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Die Serie IC706MKIIG hat zwei verschiedene Endstufen, was sehr wenig bekannt ist. Die zuerst produzierten Geräte MKIIG hatten Endstufentransistoren mit der Bezeichnung J7044. Gegen Ende 2003 gab es wegen auftretender thermischer Probleme dieselbe Typenbezeichnung MKIIG mit einer neuen Endstufe, deren Transistoren die Bezeichnung RD70HVF1 tragen. Die alten Transistoren sind weltweit nicht mehr erhältlich. Man konnte die alte Endstufe auf die neuen Transistoren umrüsten, was aber sehr zeitaufwendig war und solide Kenntnisse erforderte. Die Geräte der neuen Serie haben dann Seriennummern mit 150xxxx. Es ist folglich nicht empfehlenswert einen IC706MKIIG mit den Transistortypen J7044 zu kaufen. Die Geräte IC706 – IC706 MKII sind davon nicht betroffen. Vor einigen Jahren wurde das Problem im Internet veröffentlicht, aber nur wenige Amateure haben es gelesen.

706MKIIG/775(DSP)Finals
These two, probably others, and any manuf. who used the J7044 MosFet for a final, have a terminal issue. The finals (SR(F or K)J7044(MP) are no longer available. I have tried to contact a few sources, and a couple of parts hunters.. no Stock, No availability. The PA in the MKIIG was changed in about 2004 to a newer (totally different RD70HV)(New/Old Finals pic) device. You can swap out PA units for about $500! This includes the finals (no drivers)(706MKIIG only) A bit spendy, but at least there is a fix.

The 775(DSP) has had very few cases of Final failure. The 775(DSP) PA unit is also pre-designed to use the MRF140’s, the MKIIG cannot. The 706 MKIIG has had more cases of final failure than the 775, more MK2G’s sold out there too, than the 775.

Beware buying used MKIIG’s. The Serial number change is OLD > 0xxxxx, Newer 15(or 16)xxxxx.

I had the unique oppurtunity to evaluate the old 706 MKIIG PA unit and the new one. The primary difference between the old final and new final, is the package. Performance criteria is actually almost exactly the same. The HF transformers and componets are the same between the two boards. The driver (old MRF1508, New MRF1518) is different on the new board, but is basically a newer design, with the same spec’s.

On the VHF/UHF side I was able to grind away enough board and fit the new final in place. I needed to move the filter caps (input and output) closer to the body of the transistor, but otherwise it worked perfectly.

This will not be as easy for the HF side of things, as one finals has quite a few bottom board side lands that would be cut or damaged. If I get the chance to do this, I will report back on how it went.

sdr