The AM Forum

Any difference in NF when using LO injection on G1 or on the deflector electrodes?  I've searched a bit on Google and can't find much information on the NF when using either injection technique.

Pete

Haven't tried it both ways, Pete, but I'd suspect that since the deflection plates wanna see some voltage it'd be better to use the grid for the input signal and inject the LO at the plates.

I do know that the NF is more than adequate without using an RF amp by using the grid.  You can also apply AVC voltage at the grid.

The RX I built using this arrangement (3 6BA6 IF stages, for smooth AVC control) was almost silent, and the signals had no noise modulation on them. 

All I can say is try it both ways and see...

Hi JN

I'm going to try 6EH7s in the IF stages.  Wish me luck:)

I can see some advantage with G1 LO injection for the PD stage, that might allow balancing out BFO feed through and leakage that could affect the AGC range.  IF injection voltage for the deflectors shouldn't be an issue at the final IF.

Pete

I had considered that, but I spoke with someone (can't remember who, but he has a web page) who built a SSB xcvr using 6EH7s and he said he had a lot of trouble with IF oscillation.  They are frame grid tubes with high IMD immunity but also very high gain.