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I think it mainly depends on what you want to use for a power source. 9V will use ~1.3A in transmit, 12V will be under an amp (working from memory here!) 12V is tempting to use a nominal 12V source, but fully charged it will be more than that (13V or more!) So you'd need (read: should have!) a regulator to limit it to 12V anyway...

There's been discussion here that swr and other factors can push the voltage limits of the BS170's. Hans thinks he's got that under control, in the QMX, FWIW.

At this point, I might consider building for 9V and then use a Buck/Boost converter with output set to 9V, to adapt to the voltage that's actually available. Downside is possible noise from the converter, and a slight loss of power efficiency. Upside is the operating voltage of the BS170's will be more stable, and maybe more safety margin on the voltage. (Maybe not, too-- Lower voltage should mean more current being switched off, which could translate into a larger di/dt spike! :-( )

I like the idea of 9V/Buck-Boost because it strikes me as relatively foolproof, re: supply voltage.? I don't know if anyone has compiled BS170 failures for QMX vs 9 or 12 volts...

Good Luck!

73, Paul -- AI7JR

Well I'm back;

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Ludwig, since we determined that Q507 was good (until I broke the legs off), is there anything else that I need to pay particular attention to, to determine why there is no output power. I was going to wait to reinstall the parts that I uninstalled to avoid damaging while I removed Q507, but I think I will assemble everything and reference your last message you sent with the voltage information of some surrounding parts. What is your recommendation as far as winding T501? 12V or 9V? Is one more successful than the other as far as you can tell? If I need to rewind T501 back to 9V, I'd rather do it now while that portion of the board is partially empty.

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As always, thank you and the others so much for the input and help to get this radio working.

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73

James

KA9TII? ?

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Paul -- AI7JR