[Amps] HD HF amplifier recommendations
weeksmgr at hotmail.com
Wed Feb 8 21:37:13 PST 2012
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 QRZ.com 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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