With a span that long between the two ends you would end up with very significant droop at the center of the antenna if that's where you feed it with your transmission line.  Anything longer than 100 feet I use a center support to get away from the droop problem.  Also, you have to consider the tree sway, so you really can't pull the wire too tight...the supporting ropes or wire will stretch and break under high wind conditions.  I once used a center-fed wire 178 feet long (extended double zepp for 40 meters) and fed it with 90 feet of window line; it worked great on all bands, including 160 meters.  I used 90 feet of window line to avoid getting a voltage max on the transmit end.

Back in the old days people used dummy loads to tune up their amplifiers...not anymore.  I can't have a QSO without someone tuning up on the frequency.  I use a solid state amplifier so there is not tune up involved.  When I had the Alpha amplifiers I would dial in the settings for each band and go without tuning up.

Could also be a bad connection at the antenna.  I heard someone on an 80 the other day who was operating a CW contest on 160.  I sent him an email and he found the problem...a bad connection feeding his inverted L.

The original post is almost 5 years old.  I'm sure that by now he's figured out what to do.

I'm glad I sold my Alpha amplifiers several years ago.  Sounds to me like the company is operating on thin ice.

Don't say "contact" or "break."  Simply give your call and someone will answer you.

Snow won't affect your antenna tuning or performance.  The base of my 160 inverted L is in 2 feet+ snow and it works just fine. 

You're better of using one or the other.  But, if you use both make sure the elevated radial system is not connected to the ground radials.  I assume you're doing this for testing purposes.  I had 8 elevated radials on 160...I had better luck using a 50 radial system laying on the ground.

You could install a random vertical wire in the tree and secure it to one of the highest branches...sloping it down toward the trunk of the tree.  You would do best by using an auto tuner at the feedpoint if you intend to used it on more than one band.  You should also bury a ground screen (radials or wire mesh) under the feedpoint to reduce your ground losses.  I use a tree to support my 160 meter inverted-L and it works well.

I've had two Alpha amps in the past.  The 76CA and 89.  Both worked flawlessly.  The Eimac tubes were somewhat of a problem...bad filament weld on one and intermittent internal short on the other.  I sold my 89 a few years ago...sometimes wish I had it back.  I replaced both amps with Icom PW-1's.  So far I've spent $2200 on getting one of them repaired.

I use a two-wire switchable beverage.  I have room for a 1000-footer but I decided to try 300 feet.  It works so well I've decided not to extend it.

That's what I use for my antennas...the stranded type.  After a few months/years of exposure to the elements you will see the coating fall off or dangle from the insulation. 

I'm surprised the fuse did not blow and protect the output devices when you shorted the terminals.  I hope this was done by accident.  I had a problem once with the 35 M; it took a lightning hit.  I replaced all of the output transistors plus that IC and it worked fine afterwords.

The other thing you should do is turn off your noise blanker.  It tends to cause strong signals nearby to appear on your receive frequency.

As long as they don't start galloping I would not worry about the singing.