This is still kicking my butt.? I have been completely rebuilding the stages from scratch.? All parts removed, traces checked, then all parts replaced with new.? Q90, the pre-driver, and the final stages are working.? The pre-driver Q911/Q912 are still running away as they rapidly heat.? They start at 20 mA of bias and the voltage increases across the 11 ¦¸ emitter resistors at a rate of about 1-2 mV per second.? I've removed, checked, and replaced all of the transformers multiple times.? 2N2222As replaced multiple times.? I've built multiple kits with SMD parts - flux, 60/40 solder, and 600¡ãF on the WES51 iron haven't let me down yet.? The pre-driver had zero bias after replacing everything except R90 and R93, and the three caps.? After replacing the three .01uF caps, I got 2 mA of bias.? After replacing R90 and R93, there's no change.? Signal is getting through the chain and relays - I can trace the signal through the stages to the antenna - it's just that the pre-driver's cutting the signal roughly in half.? This doesn't make any sense.
Does any of this sound even remotely familiar???
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On Mon, Nov 19, 2018 at 03:58 PM, ajparent1/KB1GMX wrote:
On Sun, Nov 18, 2018 at 10:32 PM, AndyH wrote:
The RF chain is behaving very differently after than it did before.? When I first completed the mods, all of the stages had consistent current draw, the 2N2222A stages were set to 20 mA, and there was no excessive heat from any of them.? Now, however, Q911 and Q912 start at 20 and within about 5 or 8 seconds run up to 50 mA and start to cook.? And since the fuse blew, output power hasn't exceeded half a Watt.
Obvious that you popped something.
FYI if the bias on the 2n2222A (remember not the crap plastic PN2222) is climbing is to while transmitting
full power or at Zero power (no modulation)?? If its climbiing did you also mod the bias for the
2n2222s(all of them?)?? IF the power is climbs with no power out make sure your output transformer is
actually sending power through all those relays to the antenna.
Allison
