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![]() Yes it does. Drake did an excellent job when they designed and manufactured the L-4B. Well, I'll say this- it sure is a pretty amp, with that lovely blue glow from those meters and that warm glow from those beautiful filaments. Mine was cranking my signal out in fine style the first 24 hours of the dx contest, getting me easily across the pond to all over Europe from NJ on 80 meters and making me quite proud. I wasn't even transmitting when all of a sudden..... ka-pow ! a flash of light from the power supply, and I dove for the power switch, and unplugged the line. Then the smell of burning something or other. So far here's what I've determined, then we can debate how excellent it was designed. There are 2 bleeder resistors up on top of the PS on either side of the transformer. They are 50k at I guess about 50 watts, and if so, are within spec even at 3000 volts. One of them opened up for some reason, and I can't think of a eason for a bleeder to fail other than it just got to be too old. Now, 120 volts is derived from the bottom of the bleeders through another power resistor of about 5 k, I forget exactly. This positive 120 volts is used for the antenna relay and in standby is applied to the CT of the filament transformer to cut off the tubes in standby mode. So when the bleeder opened, the HV probably went up a little, and the tubes drew some extra current, I don't know how much, or how long but eventually it blew a little 0.82 ohm fuse resistor in the HV lead. Still TBD is how much damage was done to the tubes due to the loss of bias. I really don't like the way they get bias and will consider putting in a little 100 volt transformer in the RF section to derive my own bias. In fact it could even be redundant, fed in parallel with the original through a diode. Now I am searching for a replacement bleeder, has to be the exact size as the original because there isn't any extra room in the PS. Gee I'd like to put in a bigger bleeder, because bleeders should not fail. Wonder if Drake considered this senario when the L4 was designed. Maybe so, maybe they figured no serious damage could come to the tubes and eventually the PS failed safe and stopped before the house caught on fire, because this could have happened when I wasn't in the shack. Rick K2XT |
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