Peter, from what I can see, from your results the drive power vs. your power output I would say is about what you should expect.
Remember running the L4B on 120V the amplifier will not be as efficient as running on 220V. Also, running the amplifier on a standard 120V, 15A house circuit is not near what the amp requires. The specification for the L4B running on 120V requires a 30A circuit minimum. So when you are running the amp on a standard house circuit the primary voltage is probably dropping down to something much less than 120V. That is why I say from the measurements you indicated using a 120V house circuit, the results are about what I would expect to get. For maximum efficiently of the L4B it should be run from a 220V 30A dedicated circuit. Also you drive level should be closer to 100 watts drive. Under that condition, I would expect an output ranging around 1200 watts on 80 meters to 1000 watts on 10 meters. If you need to drive the tubes harder to get the output level the tubes may have become weak over time with use. Try your L4B on 220V on a dedicated 30A circuit, I think you will see a world of difference. Ron / WB4HFN -----Original Message----- From: drakelist-boun...@zerobeat.net [mailto:drakelist-boun...@zerobeat.net] On Behalf Of Peter Alterman Sent: Saturday, August 28, 2010 5:08 PM To: drakelist@zerobeat.net Subject: [Drakelist] L-4B follow-up Hello Fellow Drake Fans, To recap: The wattmeter on my Palstar AT1500DT reports that I'm getting variable output from my L-4B on dedicated 120v house circuit. On 40 it looks like 800-900 watts out, but on 15 maybe 500. The matched 3-500Zs are about 5 years old, the power supply was rebuilt from kit (Evan may even remember my plaintive cries for help) and I keep a muffin fan over the power supply sucking warm air out. So I promised to do some testing and report back. Here's what I found. First, the setup: Yaesu FT-1000MP Mark V via RG-8X to Drake L-4B L-4B output via RG-213/U to Palstar AT1500DT Output via RG-213/U to Balun Designs 1:1 choke balun (unun) 5 kW model 1115du to Heath Cantenna via RG-8/U patch cable 10+ minute warmup 2600 volts key up in SSB mode 120v AC on a dedicated 15a. circuit Grid current @ 200ma. The results: Band Freq est.drive volts/keydn ma/keydn meter on usual antenna 80 3545.41 40w 2250 520 800w 700w 40 7012.54 72w 2250 520 800w 900w 20 14063.85 68w 2250 520 700w 600w 15 21045.28 70w 2250 550 700w 500w 10 28045.11 80w 2200 620* 600w 450w Caveats: The Cantenna is by no means the best dummy load but it worked. I have no idea whether the Palstar wattmeter is anywhere near calibrated and it may be frequency-sensitive. Have no idea how accurate the L-4B meters are, but the voltage readings seem to be spot-on, e.g., 1700v in CW/Tune and 2600v in SSB modes. Notes and Observations: 1. Regardless of the accuracy of the Palstar wattmeter, I WAS cranking up the RF power knob on the Yaesu, so I am sure the variation in required input drive is real, though the actual readings are open to question. 2. Also, I only allowed the amp to draw 620 mils on 10 for a few seconds, for test purposes, to keep the drive @ 200 grid mils common. When I backed the drive down to 550 ma on the plate on 10, the grid showed 160 ma. and the wattmeter read 500w. 3. The higher the frequency, the more a minor SWR imbalance showed on the Palstar meter, though never more than 1:1-1. I suspect that this means the Cantenna is not a perfect 50 ohm resistive load; but then, we knew that. 4. The output readings on the dummy load differ sufficiently from what they are with my antennas connected (see above) that it suggests I could do well by doing some work on the transmission lines, coax switch, etc. Nevertheless, something seems to be sub-optimal with the L-4B. It may be time to do some work on the RF deck. The question is, what? Your thoughts and wisdom most welcome, Peter W2CDO _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
