Why are all going crazy about reducing power of a single 6146? Leave it alone and install a 3db or 6 dB attenuator at the antenna output. Either 1/2 power or 1/4 power respectively. Case closed. The rig will be left in resellable condition, and when you want the original level back... just remove the attenuator. I do it with a double pole double throw coax relay (any relay will do)when the lower level is needed. This is alot less work and is foolproof. George KC
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Geoff Edmonson Sent: Monday, April 07, 2003 11:43 PM To: amradio@mailman.qth.net Subject: Re: [AMRadio] re: Ranger driving Thunderbolt Jeff: Please forward to AMReflector for me as I cannot mail to the reflector from work. The tube in the final is not what sets the loading. It is the ratio of Xcp to Xcl in the pi-network that sets the loading. You could replace the 6146 with a 6AQ5 and it would only serve to melt down the 6AQ5, but before melt down the thing would be loaded the same. You can run 20 watt with a 4-1000 if the loading ratio is correct. If you need to drop the plate current (and RF output) simply add more capacitance across the output connector (in parallel with the loading capacitor). The plate meter in most of these small rigs measures cathode current. This means it includes screen current with the plate current. It is possible to reduce the plate current at resonates to very little (like 5-10 ma) but he meter will show maybe 25-30 ma. This is because as you reduce the plate loading the screen current will increase. This phenomenon will cause a slight increase in RF output as the plate tuning is moved off the dip (resonance). You can increase the value of the screen resistor to reduce this effect and make the cathode current meter read lower. If a separate power supply is used for the plate supply of the small rig then a small variac can be used to reduce plate and screen voltage at the same time this will allow the plate loading circuit and screen circuit to remain unchanged while reducing output by means of a lower supply voltage. Good Luck John, WA5BXO _______________________________________________ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
