[AMRadio] Re: need help


Mike Dorworth, K4XM k4xm at arczip.com
Sat Oct 22 13:00:00 EDT 2005


That would do the bias supply but he is talking about the peak RF voltage to
make the tube work. Peak RF voltage is a hair less that the 130 volts for
grid current less AB-1 operation.
----- Original Message -----
From: <bcarling at cfl.rr.com>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Saturday, October 22, 2005 12:20 PM
Subject: RE: [AMRadio] Re: need help


> 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.
> > > >>
> > > >>
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