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[NG1J]

After the frustration asoociated with a waning sunspot cycle and playing in last weekend's IARU contest, I'm starting to think an amp is in my future.

But, having never run more than barefoot, I have a couple of questions.

I'm considering pairing an AL-811 with my FT-990.  Now I know the AL-811 has a tuned input so I assume I would rarely have to use my rig's ATU because the rig should be "seeing" 50 ohms at the amp.  BUT I assume I would need a tuner between the amp and my antennas (40M Windom & Sigma-5)

Am I thinking correctly?  Am I missing anything?

Thanks
Frank, NG1J

[WB2WIK]

You'll need the Yaesu's auto-tuner on 12m and 17m, because the AL811 uses the 10m and 15m positions of the bandswitch, with tuned inputs for 10 and 15, on those two WARC bands.  If you never operate 12 or 17, then you won't need the auto-tuner in the Yaesu.  Or, you can re-tune the 10m and 15m input networks on the AL811 for 12m and 17m, but then you'll need the tuner to go back to working 10 and 15.

Whether you'll need a tuner with the Windom and Sigma-5 depends upon how well matched they are for your frequencies of interest.  Since the Sigma-5 has bandswitching matching networks built into its feedpoint, it should provide a pretty good match on all five bands and I can't see why you'd need a tuner with that.  The AL811, like most all "tube" amplifiers with pi-networks or pi-L-networks, can easily produce full power with no detrimental side effects into mismatches of about 3 to 1 (SWR = 3) or so and won't need any sort of tuner to do so.  You'll need a tuner if your mismatches are much higher than that.

WB2WIK/6

[KO4NR]

If unsure of your antenna or you can't continously and accurately measure the swr at the output of the amp I suggest you use a tuner.  A bad connection, rain water leaking in a connection, tree limb falls, whatever, can cause problems.
73,
bill

[NG1J]

*Maybe* I can save a couple of bucks on the tuner....

I just did a quick check of my SWR on the bands and found it to be less than 3:1 (but there's a twist).

I know from experience with the windom that a tuner will be required if I do any operating on 80.  Even so, I'm sure the antenna will be a "cloud warmer".

I guess I got luck with the Sigma5 as the SWR on 20 appears to be less than 2:1 in the CW portion.

Here's the twist.... namely, the Sigma5 20M SWR....
The SWR meter on the 990 reads 1.5:1 +/- BUT my (old) MN4 (which, BTW, would have to go as it can only handle up to 300W) reads just shy of 3:1.  Which is to be believed??

[KO4NR]

I'm more apt to believe the 990 but if I was you I would borrow a good SWR meter and double check them.

If you do not use a tuner keep the SWR meter inlice with the output of the amp so you can immediately see any problems.  High SWR running power is bad news for the amp, antenna and the coax.  

73,
Bill

[N0TONE]

You won't need the tuner in your Yaesu except for the WARC bands as mentioned earlier.

And the REALLY good news is this: You won't need a tuner AFTER the amp!!!

The tuner in your FT-990 probably can't handle much over 3:1.  The pi network in the AL-811 handles that range with ease.

But, even if it doesn't, you do NOT risk damaging the amp as long as you keep plate and grid current in limites.

When you tune the pi-L network on the amplifier, you will be adjusting to achieve a specified plate current.  After getting the right plate current, check the grid current.  If the grid current is within limits, then you can operate the amp safely - and don't care what the SWR is.  If the grid current is too high, and you have the LOAD control fully clockwise, then you can simply reduce the drive from your FT-990 to keep the amp's grid current in line.  Whatever power you can get without exceeding grid current limits, is perfectly safe.

The old tube rigs were just as rugged.  With tubes, you give up the convenience of no-tune, but you gain the advantage of "can't break it if you watch the meters".

Also, if you connect the ALC line between the amplifier and the FT-990 and calibrate the ALC (instructions are in the Ameritron manual), then the amplifier will automatically reduce your FT-990's drive power if grid current starts getting too high.

AM