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1st AMP AL-811
- Thread starter W1MSG
- Start date
yep, i was a little confused by : "...but close enough to where the radio is shutting down the power due to a high vswr ." , but,i thought that i had 'dain bramage too
Ok so now I am dangerous, I have some what of a clue what I am doing tuning up the amp, I have the Pi network tuned up to reduce the vswr to the radio and thats working Great.
Now Ameritron talks about tuning it gives initial settings for what ever band you are on.
So for instance it says 4 1/2 on Load and 8 1/2 on Plate (tune) start at zero out put on the radio and increase the output until either you reach 450 mA on the Plate Current and no more than 150 on the grid current.
Ok got that, no problem.
Next I tune it for peak out put starting with the Plate (tuner knob) and I do this just till it dips then back it down just a hair. Watching the meters not to exceed the above values on the meters, now I start adding a bit more drive until I get up in the 500 to 600 watt range.
Now I know the Grid Current is not suppose to go above 150 but the Plate current does in fact go above the 450 in order to get max output. Should I be keeping it at or below the 450 or does that not matter after the initial set up?
Still learning and the manual on tuning sucks ...
Now Ameritron talks about tuning it gives initial settings for what ever band you are on.
So for instance it says 4 1/2 on Load and 8 1/2 on Plate (tune) start at zero out put on the radio and increase the output until either you reach 450 mA on the Plate Current and no more than 150 on the grid current.
Ok got that, no problem.
Next I tune it for peak out put starting with the Plate (tuner knob) and I do this just till it dips then back it down just a hair. Watching the meters not to exceed the above values on the meters, now I start adding a bit more drive until I get up in the 500 to 600 watt range.
Now I know the Grid Current is not suppose to go above 150 but the Plate current does in fact go above the 450 in order to get max output. Should I be keeping it at or below the 450 or does that not matter after the initial set up?
Still learning and the manual on tuning sucks ...
well, when ya are in there "clipping that green wire",..... do your self a favor.
check EVERY joint for a cold solder, tighten all nut/bolts ect.
turn the unit upside down and (gently) shake it.
MFJ is infamous for leaving "stuff" inside units.
of course,...... be sure to discharge the caps first
Whats the best way to ensure the caps are discharged and its Ok to stick my grubby little fingers inside the amp?
Thanks
Let the amp turned off for a while so the caps discharge. the amp has a safty switch for when the amp is opened.
Probably the most common way of discharging those caps is with a 'chicken stick', or a fairly long screwdriver. Using the screwdriver, you hold the shaft against the cabinet and touch a plate cap with the pointy end. The biggy is to hold the shaft against the metal cabinet BEFORE touching, and WHILE touching that plate cap. That's done one handed, by the way. What'da you do with the other hand? A very good place for it is in a back pocket. That way, if you do happen to get a shock, you only pinch your butt, not something more precious (if that makes sense??).
A 'chicken stick' is basically a metal probe with an insulated handle connected to a cable and alligator clamp that clips onto the chassis/cabinet of the amplifier You're giving those electrons a path to ground that's NOT through you.
Touching those plate cap(s) more than once is a very good idea. You might also look at the end of that 'chciken stick' or screwdriver after doing so. There is commonly a 'bite' taken out of it. May not be huge, but now imagine it was your finger that was 'bitten' to the same 'degree'. It's very seldom that someone ever makes that sort of mistake a second time...
- 'Doc
A 'chicken stick' is basically a metal probe with an insulated handle connected to a cable and alligator clamp that clips onto the chassis/cabinet of the amplifier You're giving those electrons a path to ground that's NOT through you.
Touching those plate cap(s) more than once is a very good idea. You might also look at the end of that 'chciken stick' or screwdriver after doing so. There is commonly a 'bite' taken out of it. May not be huge, but now imagine it was your finger that was 'bitten' to the same 'degree'. It's very seldom that someone ever makes that sort of mistake a second time...
- 'Doc
In the broadcast business we used to call them Jesus sticks. If you didn't use one before working on a TX, Jesus was the next person you would be seeing.
Also if the bleeders were not working you usually ended up shouting his name loudly as an involuntary reaction to the ensuing fireworks upon application of the Jesus stick. The ones we used were shaped like a cane held upside down. They had an insulated handle and the metal hook end was bonded to the TX chassis.
select the High Voltage meter setting. you should be able to see the meter reading drop.
you STILL need to follow elect safety procedures. this is NOT some little cb amp with a 12vdc power supply, it CAN kill you.
chicken stick, one hand only in the amp at all times, no jewerly, rings,watches ect. always use a multimeter to check for voltage.
as long as i'm om the band wagon,........ you did connect the external chassis ground,...... right?
As a matter of fact, no. If I'm inside an amplifier there's typically no external connections at all. Discharging to chassis ground will 'de-fuse'/discharge those capacitors just fine. Using an external safety ground isn't a bad idea though.
- 'Doc
- 'Doc
Yup chassis is grounded with a 5 foot 1" braided copper strap out to the ground bar and then that to the grounding rod.
The MOD id done and I didnt have to stick my hands down in the amp, the green wire was real easy to snip.
Now I am having withdrawals on the IC-7000, its on its way to Michigan, talked to tech support yesterday and its about a 2 to 3 week turn around.
The FT-857D is all set up and operational ! No HF in the Explorer for a while...
Craig
The MOD id done and I didnt have to stick my hands down in the amp, the green wire was real easy to snip.
Now I am having withdrawals on the IC-7000, its on its way to Michigan, talked to tech support yesterday and its about a 2 to 3 week turn around.
The FT-857D is all set up and operational ! No HF in the Explorer for a while...
Craig
i've been kinda thinking about your comment "the Plate current does in fact go above the 450 in order to get max output" ,.... where did you get the 450mA max plate current from? 450plate/100grid "seems" about right for the inital load "guess-timate", but i think final load of 750 (MAX!!!) should work.