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Re: [Amps] HD HF amplifier recommendations

Subject: Re: [Amps] HD HF amplifier recommendations
From: "Roger (K8RI)" <>
Date: Thu, 09 Feb 2012 02:46:08 -0500
List-post: <">>
On 2/9/2012 12:37 AM, Charlie Young wrote:
> 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.
Likewise. Being retired my budget limits me more than anything else and 
the one acre size of my lot comes next.  Fortunately when they rezoned, 
a letter to the zoning commission resulted in Ham Radio being exempted 
from the zoning. As I understand it, we are exempt except from set backs.
> 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.

Likewise, my previous car was a TransAm with a Corvette engine.  Having 
all that power and big tires saved my life. The stop light ahead changed 
to red and I stopped. I noted a van approaching from behind in my lane 
and he was moving fast.  When He reached the point where I knew he was 
never going to stop I leaned on the horn and floored it. Fortunately all 
the crossing cars stopped except one and I made it through just behind 
him. I hit 70 in a 35 zone as he almost touched my rear bumper. I 
changed lanes and he passed me without ever slowing down.  If he'd hit 
me at that speed the front seats would have ended up in back.

> 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.

For me I want an amp that will do the legal limit without limitations be 
it 5, minutes, 30 minutes, or 24 X 7 for 365 days a year. To me it 
represents a safety factor.
As I chase DX on 40 and my 20 through six antennas are down at the 
moment it is rare to operate without the amp.  OTOH I did work some DX 
the other night before I even turned on the filaments.  The band was 
fairly quiet and signals were strong so the 200 watts from the exciter 
were enough.

My goal, whether I ever tackle it or not is to build amps for HF, 
6-meters, and 2-meters using 4CX3000s.
> I have been licensed for 50 years
I was first licensed in 61 (April or May)
>   and have never made a 30 minute key down transmission, even back in my AM 
> days.
When FM first came along I'm afraid I held the record for timing out the 
>    It is doubtful if I have made a 5 or 10 minute key down transmission.
Now those I have done many.  I have absolutely no sense of time.
>    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?
I like to be able to spend the evening chasing DX or rag chewing and 
only find the transformer warm.
> 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.
That sounds good and I agree with it, but unfortunately several amp 
manufacturers have rated amps well beyond the ratings of the tubes and 
power supplies used.  Often the ham tries to get the last watt out of 
the amp and runs considerably more dissipation on CW or SSB than the 
tubes or PS are rated for.


Roger (K8RI)

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