[AMRadio] Re: need help |
bcarling at cfl.rr.com
bcarling at cfl.rr.com
Sat Oct 22 12:20:09 EDT 2005
What about using a 130 volt 5 Watt zener diode in the cathode? On 21 Oct 2005 at 21:48, Gary Schafer wrote: > I just looked up the 4-400 and I see it requires more bias than I had > remembered for AB1 operation. It requires -130 volts with 2500 on the plate > and 750 on the screen. > So a 50 ohm resistor with 100 watts would only provide around 100 volts peak > drive voltage. Not quit enough. > > A 100 ohm resistor should provide around 140 volts peak with 100 watts. That > should work with little drive to spare. > Probably the easiest would be a 200 ohm resistor (close to the 170 ohm > resistor). A 4:1 balun should match it close to 50 ohms. > A 200 ohm resistor and 100 watts should provide close to 200 volts peak > drive voltage. > > I did this setup (balun and resistor) with a pair of grid driven 1625,s > driven by my 20A. It worked well. Voltages were less of course! > Stray capacitance will change things a bit. > > 73 > Gary K4FMX > > > > -----Original Message----- > > From: amradio-bounces at mailman.qth.net [mailto:amradio- > > bounces at mailman.qth.net] On Behalf Of ne1s > > Sent: Thursday, October 20, 2005 12:30 PM > > To: Discussion of AM Radio > > Subject: [AMRadio] Re: need help > > > > With a 50 ohm grid load on 4-400s, I think you'll find you'll get very > > little amplification from the stage - the 40400 grid(s) want(s) to see > > more > > voltage. I went throught this exercise one (on paper), so went with a 1:16 > > balun into a 800 ohm non-inductive resistor network in the actual design. > > Problem was, I couldn't make it broadband enough to cover more than 3 > > consecutive bands at a time, and finally resorted to a T network on the > > input, loaded with about 2000 ohms worth of resistors. > > > > -Larry/NE1S > > > > Gary Schafer writes: > > > > > The input impedance should be very near what the value of the resistor > > is. > > > In this case 170 ohms. The 4-400's will most likely be run in AB1 so no > > grid > > > current. > > > I would put in a 50 ohm resistor instead. You should get enough drive > > with > > > it. Figure what the bias voltage will be on the tubes. Then figure what > > the > > > peak voltage will be from the exciter at 50 ohms. If the peak voltage > > will > > > be greater than the bias voltage on the tubes then you have enough > > drive. > > > > > > 73 > > > Gary K4FMX > > > > > >> -----Original Message----- > > >> From: amradio-bounces at mailman.qth.net [mailto:amradio- > > >> bounces at mailman.qth.net] On Behalf Of esieb at sympatico.ca > > >> Sent: Wednesday, October 19, 2005 10:46 AM > > >> To: amradio at mailman.qth.net > > >> Subject: RE: [AMRadio] need help > > >> > > >> I'd have used an MFJ 259B to actually measure the input Z. > > Alternatively, > > >> you can always use a small tuner to "tune" the input. I do that > > anyway > > >> with my Drake L4B, (use a small MFJ mobile tuner with meter). > > >> > > >> 4-400's, eh? Nice amp! If your plate voltage is high enough, you > > ought > > >> to > > >> get serious power out of that baby! > > >> > > >> 73, Ed, VA3ES > > >> > > >> > > >> From: Edward B Richards <zuu6k at juno.com>: > > >> > > >> I want to drive a linear amplifier with a rice box that requires a 50 > > ohm > > >> load. > > >> The linear amp uses an input to a 170 ohm, 80 watt swamping resistor to > > >> ground, then > > >> through a .001 mfd capacitor, then through a VHF parasitic suppressor > > >> consisting of 4 turns of wire around a 47 ohm resistor, to the grids > > of > > >> a pair of parallel connected 4-400A tubes. > > >> > > >> What I need to know is the impedance of the input. Is it close to 50 > > ohms > > >> or do I need to use a matching network between the rice box and the > > >> linear amplifier. > > >> > > >> > > >> ______________________________________________________________ > > >> AMRadio mailing list > > >> Home: http://mailman.qth.net/mailman/listinfo/amradio > > >> Help: http://mailman.qth.net/mmfaq.html > > >> Post: mailto:AMRadio at mailman.qth.net > > >> AMfone Website: http://www.amfone.net > > >> AM List Admin: Brian Sherrod/w5ami > > > > > > > > > ______________________________________________________________ > > > AMRadio mailing list > > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > > Help: http://mailman.qth.net/mmfaq.html > > > Post: mailto:AMRadio at mailman.qth.net > > > AMfone Website: http://www.amfone.net > > > AM List Admin: Brian Sherrod/w5ami > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio at mailman.qth.net > > AMfone Website: http://www.amfone.net > > AM List Admin: Brian Sherrod/w5ami > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio at mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami >
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