L7 wattmeter is average reading as can be determined by looking
at the schematic in the manual. If I recall correctly, it is
identical to the Drake WH-7 (and W4) wattmeters. The sensing
point is located between the T/R relay and the output connector.
73,
... Joe, W4TV
> -----Original Message-----
> From: amps-bounces@contesting.com
> [mailto:amps-bounces@contesting.com] On Behalf Of Bob AD5VJ
> Sent: Tuesday, April 06, 2010 8:05 PM
> To: 'Michael Tope'; amps@contesting.com
> Subject: Re: [Amps] DRAKE L-7
>
>
> Hi Mike
>
> The power supply I am using came with the amp. It is enclosed
> in a rectangular case which is a sort of lattice material. It
> sits on the floor as it is quiet heavy. I am not sure if it
> is the stock one or not. The amp as I received it had many
> mods done to it including one so it will work on all bands.
>
> It is my first amp and I am not really sure how to evaluate
> it fully yet although I am attempting to absorb the manual.
>
> As a example I cannot find anywhere in the manual as to what
> type of meter is the power meter (watts) not sure if it is
> rms or peak reading. Also not sure if it is reading output to
> the antenna or input to the circuit.
>
> Bob AD5VJ
> > -----Original Message-----
> > From: amps-bounces@contesting.com
> [mailto:amps-bounces@contesting.com]
> > On Behalf Of Michael Tope
> > Sent: Tuesday, April 06, 2010 9:00 AM
> > To: amps@contesting.com
> > Subject: Re: [Amps] DRAKE L-7
> >
> > Bob,
> >
> > Are you using a stock L-7PS or L-4PS power supply with your
> L-7? The
> > numbers you are getting don't seem to make sense. The L-7 runs the
> > 3-500Zs in zero-bias mode similar to the SB-220. The resting plate
> > voltage in the SSB position is something along the lines of 2500 to
> > 2700 Vdc. Using your numbers, 3200 volts x 640mA = 2050
> Watts DC input
> > x 65% efficiency = 1330 Watts.. If the 1800 watt number were real,
> > your efficiency would have to be on the order of 90%. Also, at 1800
> > watts output with only 100 watts drive, the L-7 would need close to
> > 13dB gain.
> > That isn't a realistic number unless the anode voltage really is up
> > around 3600 Vdc in which case I think you do get a little more gain,
> > but
> > regardless of gain, efficiency is never going to be any greater than
> > 70%. The gain of the L-7 is not much more than 10dB at stock plate
> > voltage. Using a realistic numbers for anode voltage, I get
> 2300 Vdc x
> > 640mA = 1472 Watts DC input x 0.65 = 957 Watts @ 9.8 dB gain.
> >
> > Using my L-7 just now on 160 meters with 90 watts CW drive (Diawa
> > reads 90W, FT1K meter reads 100W), I got 2100 Vdc x 700mA x
> 0.65 = 950
> > Watts = 10.3dB gain. The actual reading on my Diawa CN-720B was 900
> > watts which would correspond to 10.1dB gain. The L-7 power
> meter read
> > 1000 watts. I am not claiming that any of my numbers are super
> > accurate, but they are consistent with what I would expect
> from a pair
> > of zero-biased 3-500Zs.
> >
> > FWIW, the anode voltage reading on my other L-7 reads
> higher even when
> > I use the same power supply. I think this is from drift in
> the carbon
> > composition resistors used in the voltage divider in the
> anode voltage
> > metering circuit. Sounds like your watt meter calibration may have
> > drifted as well.
> >
> > 73, Mike W4EF..........
> >
> >
> > On 4/5/2010 7:38 PM, Bob AD5VJ wrote:
> > > I would however like to run this by you guys:
> > >
> > > I am looking at the meter right now in ssb mode and it
> shows at idle
> > 3600
> > > Plate Volts and zero plate amps.
> > >
> > > I know to get to power out to the antenna I multiply the ep by ip
> > > and
> > take
> > > away about 40 percent since ep and ip is input power not
> the output
> > power to
> > > the antenna.
> > >
> > > Leaving the amp in ssb mode and then placing my TS-850SAT in tune
> > mode
> > > (50watts output) at key down the plate voltage shows 3350 plate
> > volts, the
> > > Drake Plate current shows 580ma when the plate is dipped
> to minimum
> > and the
> > > load is increased to full output until no further change can be
> > detected and
> > > output is maximum and voltage and current are stabilized.
> > >
> > > Then I transmit in rtty (pulsing using the mark - no data) at a
> > > drive
> > level
> > > of 100w (alc at midpoint - processor off) - leaving the
> Drake in ssb
> > mode on
> > > transmit, I retune the amp using the mark pulse and the plate
> > > voltage
> > drops
> > > to 3200 volts and the plate current shows 640ma of current with a
> > power
> > > indication of almost 1800 watts output on the drake power meter.
> > >
> > > I think the power meter is supposed to be reading power out to the
> > antenna
> > > but not sure it could be power input to the plate. Doesn't the
> > > output
> > power
> > > in this case seem a little high on the drake avg power meter?
> > >
> > > Since this is an avg power meter, it would be 1.3 or so
> times this
> > > on
> > voice
> > > transmissions for PEP seems awfully high.
> > >
> > > Bob AD5VJ
> > >
> > >
> > > _____________________________________________
> > > From: Bob AD5VJ [mailto:ad5vj@ad5vj.com]
> > > Sent: Saturday, February 06, 2010 4:47 PM
> > > To: Amps@contesting.com
> > > Subject: DRAKE L-7
> > >
> > >
> > > Can someone pls tell me why when I am loading
> up my antenna with
> > > my Drake L-7, the Keyer on my IC-761 gets stuck. I have to
> > depress the
> > > VOX then turn the rig on and off to get it to unstuck.
> > >
> > > Any ideas?
> > >
> > > 73,
> > > Bob AD5VJ
> > >
> > >
> > > _______________________________________________
> > > Amps mailing list
> > > Amps@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/amps
> > >
> > >
> > >
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|