Re: Connecting QRP-PA-2008 to the Sierra
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This may be slightly OT but related.
My Sierra was suffering from the dreaded "Low Output Syndrome" and I had tried several mods to beef it up. Finally I decided to try the DLQRP 2008 amplifier so that I would have 5 w rather than 400mw on 20 m.
This amp requires both a fixed and keyed 8v. The keyed 8v is available as +8 tx off of the collector of Q4. My measurements of this showed that the voltage was only 4 v on keydown. I think this limits the drive out of buffer Q5 but I'm not sure why I'm getting 4v rather than 8v.
As an experiment I replaced Q4 (2n4126) with another PNP I had in the junk box, a 2n3906. I reasoned that since it was functioning as a switch the hfe difference shouldn't matter. But now the collector voltage is only 2 volts!
I need some advice. Do I need to get another 2n4126 or might the problem be elsewhere?