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Re: [Amps] HD HF amplifier recommendations

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Subject: Re: [Amps] HD HF amplifier recommendations
From: Charlie Young <>
Date: Wed, 8 Feb 2012 23:37:13 -0600
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Don N8ECH said:  > While I realize the bar has been set at 1500 watts, most of 
us can recall those great QST ads of the 70's and 80's with the older 
generation Alpha with a "brick on the key" at 1KW out.

Those were some effective  ads  :-)   
Most of us who frequent this reflector, even as lurkers like me, are Amp 
Afficionados.   I admit to collecting amps and repairing them for my local 
friends, because amplifiers interest me.  My old eyes can still see good enough 
to work on amps. 
The attractiveness of having "headroom" is well understood.  Going back to the 
automobile comparison,  there are "car guys" who would not think of buying a 4 
cyclinder car; only a 300 plus HP V8 would do.  The 4 cylinder will do the 
practical job that an automobile fulfills, but it won't do 160 mph top end or 
go zero to sixty in 4 or 5 seconds.   
There is nothing wrong with being an Amp Afficionado or a car guy.  I am or 
have been both.  Look on my page.  The big custom amp has been on the 
air twice for testing, both times for ragchewing on 75M with the locals. It is 
not in the operating lineup and has never been used for DXing. It has never 
been on CW.  It is pretty neat to look at, especially in the dark with the lit 
tube compartment and the red backlights on the meters and switches.  Cool!  
I have some thoughts about the 30 minute key down 1500 watt endurance test we 
have been discussing.  Roger K8RI hit the nail on the head when he said, and I 
may paraphase a bit, than any amplfier that could do this would be capable of 
exceeding FCC power limits and thus FCC approval might be problematic, absent 
some built in power output limiting feature of the amplifier.  So if an amp 
will do 1500 watts for 15 minutes, it might do 2500 or 3,000 watts for 5 
minutes, without reliability problems.  As an Amp Afficionado, I understand the 
attractiveness of having such an amp even if one never intends to run more than 
1.5KW out of it.  
I have been licensed for 50 years and have never made a 30 minute key down 
transmission, even back in my AM days.  It is doubtful if I have made a 5 or 10 
minute key down transmission.  I would never subject any of my amps, even one 
which would likely do it, to a 30 minute 1.5 KW output transmission.   Short of 
running high power AM on long winded ragchews, the likely toughest applications 
for our amps are RTTY contesting or maybe one of the high duty cycle digital 
modes, such as JT65.  If someone does not operate one of these activities, all 
that really matters is if our amplifiers will do legal limit output, for the 
necessary time, without self destructing.  We might like to have amps that 
would run 1.5 KW key down for 30 minutes, or do twice the legal limit power 
output for 5 or 10 minutes, but is that really necessary for the guy who is 
simply  looking to upgrade from an AL-811 or an SB-200 to an amp that will do 
1.5KW output? 
All of this discussion about a 30 minute key down 1.5 KW requirement, or else 
we need to be nervous about whether our equipment will melt down, may cause 
some to think it is necessary to spend big $$$ for the ultra amplifier or else 
build a heavy duty one. If we have the resources, time and money, to buy or 
build the ultra heavy duty amp, great.  However, if we don't have those 
resources there are cost effective options for achieving reliable legal limit 
RF output. 
Ameritron builds their AL series amplifiers to meet a market segment.  The 
AL82, AL-1200 and AL-1500 share the same components, except for the tube.  All 
of these are sold as legal limit amplifiers, and in fact they are all capable 
of exceeding the legal limit.  Yes, even the AL-82 will exceed 1.5 KW to a 
dummy load.  
The AL-82 achieves legal limit output without any fuss.  It is smooth tuning. 
Once you know where to set the load control on a band, the output can be peaked 
and you are good to go in zip time.   You don't have to fiddle with it for 5 
minutes to tune it up.  I would have no worries at all about using this amp for 
ragchewing, SSB or CW contesting, and of course it is used all the time for 
DXing.  If I were going to do RTTY contesting, I likely would use the AL-1500 
or the Alpha 77DX, because of the extra 500W of tube plate dissipation they 
have. For my DXing use, 1.5 KW of RTTY output has not caused any problems. 
The AL-82 is also forgiving of mistakes. I have transmitted full power into the 
wrong antenna more times than we should admit.  Once I made a DX QSO on 15M and 
the amp was tuned up on 10M.  Once I accidentally drove it with 200W 
momentarily. As much as we band hop, sometimes with little sleep, things 
happen.  The AL-82 just keeps on trucking.  I have never had any kind of heat 
or duty cycle related problem with this amp, in 3 years of heavy use.  Never 
had a tube failure.   Ditto for my 1994 vintage AL-1500, which is relegated to 
a backup role now, but at one time it was the main amplifier.   Why is it the 
backup?  It uses an expensive tube and the AL-82 uses less costly tubes, so I 
don't worry about making a mistake in the heat of battle.  
Over the last few years, I have repaired several  AL series amps for others.  I 
have replaced the capacitors and bleeders in two.  A step start relay in one.  
An open plate choke in one.  Some shorted diodes in another.   None of the 
amps, including my own, have shown any problems with the tank circuit 
components, no signs of heat, stuff melting, etc, other than a failed chip type 
loading padder capacitor, which happened when a 160 antenna fell and the SWR 
went high.      No transformer problems.  
Recently, I repaired an Alpha 91b for a friend.  He is a DX ragchewer.  What 
was wrong with the Alpha?  It had a shorted transformer.  More specifically, 
the filament and high voltage windings were shorted together.  It goes to show 
that even the more expensive amplifiers can sometimes have unexpected problems. 
73 Charlie N8RR     
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