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Machlett 3+500zg tubes

Here's what we use for 11-meter AM hot-rod operators.

The coil is #14 copper, three turns wound on a half-inch diamter. One 100-ohm 5-Watt carbon-film resistor inside, and another one in parallel alongside it. The long "tail" on each is to make it flexible enough to remove and install tubes without damaging the solder lug at the top of the plate choke.

7cfFPZ.jpg


Looks crude, but driving the amplifier hard produces a lot of harmonic energy. The parasitic choke will trap enough of this harmonic energy to overheat and cause the original 2-Watt part to fail, usually with a crack down the middle.

And if your main interest is sideband, you won't be driving the SB-220 hard enough for this solution to make sense.

But the nichrome suppressors will probably overheat if you use the SB-220 as an AM hot rod.

73
 
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Reactions: 543_Dallas and Shadetree Mechanic
Install them last night was no problem.. think I'm all set now very happy with the sb220. Very happy with the new tubes. Very good output..swapped out radios to one that has lot more swing really perks up the sb220
 
Never hurts to put a SWR meter in between the radio and the amplifier. Key the radio with the amplifier active, calibrate and then read the SWR.

This tells you how close the amplifier's input impedance is to 50 ohms. If it's really high, this can be hard on the radio.

73
 
Stick it in between the two pill and the sb220 then it brings it to a Flat match as tech said gathers another ...........so Watts..
 
552fl said:
Stick it in between the two pill and the sb220 then it brings it to a Flat match as tech said gathers another ...........so Watts..
Click to expand...

I understand what you are doing. My question was if this is normal for a sb220 used on 11 meters to have a high input swr. Is the input circuit not broad banded enough to cover 10 and 11 meters? You're about .... cans short of a 6 pack. :D
 
Must be tuning the input Circuit of the two pill going into the sb220 .. that's how the technician ran it when he installed the capacitors and and new metering board seems to help quite well..
 
552fl said:
Must be tuning the input Circuit of the two pill going into the sb220 .. that's how the technician ran it when he installed the capacitors and and new metering board seems to help quite well..
Click to expand...

If the output of the 2 pill is off or the input match on the sb220 is off the tuner might make it play better but it's still a half assed way to do things.

552fl said:
wow. didn't know that it do that many watts..thanks bbi
Click to expand...

Why do you keep bringing up watts? Here's what my bbi modified sb220 will do with weak tubes. That's the 2 pill driver in the background
20180902_202635.jpg
...and yes those 90 degree connectors get hot fast.....bad idea to use those. The rg213 gets warm too.
 
That's all it will do??should not run it like that.. better drink your 6- pack if you run it like that.
 

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