Bob,
There are pictures of the L-4PS with the following Ebay ad:
http://cgi.ebay.com/Drake-L-4B-L4B-HF-Linear-Amplifier-Matching-L-4PS-HAM_W0QQitemZ150430698367QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item23065e4b7f&ssPageName=RSS:B:SHOP:US:102
AFAIK, the L-7PS and the L-4PS are identical (the L-7PS may have come
stock with more compact electrolytics). The wattmeter in the L-7 samples
the RF signal at the output of the amplifier. The full scale reading is
switchable between 3KW and 300W for forward power and 300W for reverse
power. I believe the power meter provides an average reading.
73, Mike W4EF............
On 4/6/2010 5:05 PM, Bob AD5VJ wrote:
> 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
|