Quote:
Originally Posted by G8DLH
The anode dc load of the RF amp is 5k6. (Seems far too low to me. I would have expected something like 100k - 220k). This, in parallel with the O/P impedance of the RF Amp. could be heavily damping the tuned cct. - depending on the degree of coupling between pri. and sec. of the transformer.
Try increasing the physical spacing between pri. and sec. You'll lose some overall gain, but the selectivity should improve.
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Al - the anode load of an untuned RF amp has to be low, since the stray capacitances will be the 'real' load on the output. A few tens of pFs will only have a reactance of a few k-ohms at the top end of MW. Reducing the coupling or tapping the primary down will improve the selectivity though. I'd use an EF85 rather than an EF80 for smoother gain control.
Neil
