[AMRadio] need help


Edward B Richards zuu6k at juno.com
Wed Oct 19 21:24:26 EDT 2005


Thanks, Gary.

Ed K6UUZ

On Wed, 19 Oct 2005 20:02:19 -0500 "Gary Schafer"
<garyschafer at comcast.net> 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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