First a couple of basic checks on your measurement setup -
- make sure your scope and probes are set up correctly: most scope probes have a? 1x and 10x option, and it needs to match that same option on your scope, otherwise the readings will be incorrect by 10x
- when you measured the output, did you have a dummy load attached?? hopefully so, unless your scope has a 50-ohm termination option turned on (but most inexpensive scopes don't have an internal 50-ohm termination).
- when you measure, are you measuring peak-to-peak voltage of the sine wave, or an RMS value?? Most scopes report both; peak-to-peak is probably best for debugging
?
If the above are done correctly, you are seeing very low power out of the QMX, but real power.? 4W out should be about 40Vp-p, but Tune SWR default is 50% voltage, so about 20Vp-p.?? The 5Vp-p you measured would be 62 milliwatts (5Vrms would be 100mW).?? So please first confirm your measurements.
?
If they are correct, it means your BS170s are not amplifying the signal much, if at all - or maybe all your LPFs are turned off due to no bias current, so the signal isn't coming out.
?
Most often we don't have a bias current problem, but Jeff has noted that sometimes the L501 gets broken (one of those 330uH coils), or C504 (the big tantalum capacitor) fails.? So you could check those two items.? Also check that L504 and L514 are soldered in properly and not cracked (since I understand they are a bit fragile) - and that your diodes are not soldered in backwards.? Any of these could cause havoc with the bias current.
?
Stan KC7XE
