Just to clarify, I used 1.6 for "K", which in Ian's spreadsheet is in the middle of the range for AB: Single 8877 4KV 625mA 60% efficiency "K" factor of 1.6 = 4000 ohms plate load impedance. Jim W7RY
I donīt believe that the anode voltage drops to zero volts at 625mA anode current. 4KV voltage swing in your calculation is probably too high. 73 Peter Just to clarify, I used 1.6 for "K", which in I
Hello, it should be remembered that the values of loading capacitance, tuning capacitance and the inductance of the tank coil not only depend on impedances and frequency, but also on Q. The designer
Right. I said maybe and maybe not. I also included a link to the constant-current curve for the 8877 so he can find out for sure. 73 Jim W7RY I found that this is far from the correct value for the 4
ORIGINAL MESSAGE: (may be snipped) REPLY: The solution to this problem has been known for decades. A simple coil between tube anode and the rest of the circuit provides the equivalent of an L-network
Good point. If I lower the swing to 3800 and raise the current to 658mA to keep the same dissipation, the guesstimated plate load impedance drops to 3610 ohms. Lowering the Q to 10 then puts the load
Absolutely. I learned that trick from Carl, seems like a few hundred years ago. This design uses 3uH of "lead" inductance for just that reason. It raises the tune capacitance at 10M to a practical va
Note that this lengthens the VHF 'parasitic tank circuit' between the plate, the frame of the tune capacitor, and the cathode. So it can cause instability. This design uses 3uH of "lead" inductance f
It means squat unless you believe Measures voodoo. Kill the parasitic tendency right at the anode with a correct value L. Proper layout and construction practices even work with a pair of 4X1's on 10
ORIGINAL MESSAGE: (may be snipped) On the highest bands, the problem is another one: All that tube capacitance and stray capacitance forces us to use a Q higher than we would like! For example, on 1
Nope, its no wonder considering their attitude problem on the telephone. Carl KM1H On 10/20/2013 8:54 PM, Carl wrote: All 3 of the Command Tech amps 1/2/3 tubes used a single toroid switched for 40,
circuit is commonly called a L-PI. Typ coil values are .3 to .7 uh. And no, it doesnt make the amp unstable. A buddy recently completed a 80-10m YC-156 GG amp. Now that tube is 35 pf from anode to gr
Who talked about a YC-156? There are tubes with less capacitance around. The coil value depends on the tube capacitance. 73 Peter circuit is commonly called a L-PI. Typ coil values are .3 to .7 uh. A
Roger - Palstar is no longer in the amp business. I have the first HF2500E he built. I flew down there a few times to watch the build. I flew there to pick it up on a Friday afternoon when they told
&&&& so what ? The point is no single 8877 is gonna require a whopping 3 uh b4 the main 10m Pi-net to get it to work on 10m. Maybe .3 to .5 uh. BTW.. there is one helluva lot of current in that coil
$$$ to attend, and ask for their $$ back ! Ditto with RF consultants. Strap the bandswitch correctly as per my previous post. DONT use braided wire for the various taps, use silver plated cu strap. I