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Using a rough approximation formula like:
Ep/1.8Ip=R calculate the approximate optimum loading at the tube you want. These are only rough guesses, but will be close enough.
2000/.5*1.8 =1800 ohms.
Leave the tubes in sockets, and place a 3.6k carbon or metal film resistor from each anode to chassis with short leads. The resistance isn't terribly critical, because this is a rough approximation anyway. 3.3K's would work.
See if looking backwards through the tank with the analyzer, power off of course, yields reasonable settings of the plate and load capacitors on all bands.
You would want about 250-300 ohms of capacitive reactance on the plate side for each upper band edge.
People will get really anal about a certain value, but the truth is even if you are off by 50% there will be very little performance change. The only real danger is going to low in capacitance value, which can make the tuning mushy and the load control behave backwards. If the operating Q is 10 or 20, there will be very little change in performance.
How much operating grid bias do you have on the tubes at normal idle current settings? That determines the grid resistor size.
http://www.w8ji.com/grid_driven_tetrodes.htm
Last edited by W8JI; 02-23-2012 at 02:45 PM.
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Ok, I should have listened to my body but decided on a rework of the pi-network. I have now connected the "open" end of that coil to the antenna as also the load capacitor. So its now typical pi output. The band switch numbering was reversed and 400w out on all bands, but I still need to get the tappings right. For example max output on 20m is when bandswitch is inbetween 20 and 15m. I am stopping now as my hands are killing me with this psoriatic arthiritis. I'll do some MFJ work over the weekend.
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Just another thought. I see that my rig is showing a mis-match on the input to the grids as its not 50 ohms. What effect will a 50 ohm resisitve load, placed infront of that 390 ohmresistor, have on the grids?
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 Originally Posted by M0ELS
Just another thought. I see that my rig is showing a mis-match on the input to the grids as its not 50 ohms. What effect will a 50 ohm resisitve load, placed infront of that 390 ohmresistor, have on the grids?
All of that info is on the link I gave.
http://www.w8ji.com/grid_driven_tetrodes.htm
You have to know the bias voltage to know what grid resistance to use, or what the grid resistance you have will do.
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Ok thanks, will do some more reading. Hands are still painful, so not doing much at the moment.
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