I havent used ALC since I got rid of the Drake C Lines which were driving a
pair of NCL-2000's which were a bit touchy about overdrive in AB1. The
replacement TS-930's had adjustable power and internal ALC loops which was
all I needed.
My current amps and TS-950SD & TS-940 run at reduced power since the IMD
sweet spot is 75-80W and Im still getting 1200W out of the LK-500ZC main amp
with the original 1986 Eimac 3-500Z's.
The Alpha 76PA 3 holer has 80's tubes I bought used (got the amp as a
contest beat to death basket case) and run at 1200W and the Dentron MLA-2500
and DTR-2000 backups have their original tubes and have never been pushed.
I guess no company is getting rich off me....too bad.
Carl
KM1H
----- Original Message -----
From: "Mike Tubby" <mike@tubby.org>
To: <amps@contesting.com>
Sent: Thursday, July 26, 2012 5:47 PM
Subject: Re: [Amps] Overdrive protection
> At the risk of being somewhat controversial ... why are we using ALC
> these days?
>
> I have many radios but currently use an FTDX5000 on 6m and transvert to
> 2m. None of my tube or solid-state amplifiers have ALC. Even on HF with
> my trusty TL922 I do not use ALC.
>
> My approach has always been to tune up the amp at full power on CW/FM,
> switch to SSB, reduce drive to around 2/3rds. My 8877 on 6m produces a
> very nice 1000-1100W with about 30-35W of drive. I can use plenty of
> speech processing and a Heil headset with a "DX" element to create a
> "wall of sound" type signal for contesting and yet the signal is narrow,
> has almost no splatter and doesn't suffer overshoot or need ALC to hold
> it back.
>
> Basically I'm using the 2/3rds rule - most so-called "linear" amplifiers
> are not... at best they're approaching linear for the first 2/3rds of
> their output (to around 65-70% of their rated output) after this they
> become increasingly RF compressors. The 1dB compression point on some
> amplifiers is shocking.
>
> I cannot see the point of (over) driving an amplifier and effectively
> using ALC to "hold it back" ... it just seems to me that if you're doing
> this then your amplifier isn't big enough in the first place - to this
> end I have to say I'm with Mr. Measures... a 3CX3000 or 3CX5000
> under-run at 1500W PEP is just going to be SO SO much nicer than a small
> amp thrashed to within inches of its life ;-)
>
> Leif, SM5BSZ, has done some work looking at an FT1000D's output and the
> affects of ALC:
>
> http://www.sm5bsz.com/dynrange/alc.htm
>
>
> With solid state amplifiers things get more interesting again, since you
> don't tune them up in the traditional sense. My experience with
> building single and double BLF578 amps for 144MHz has shown that there's
> a significant trade-off between gain, efficiency and linearity depending
> which you pick to match on the load-line. Its the difference between
> 920W out at an apparent 73% efficiency (with poor IMD) or 800W out at
> 63% with good IMD... if you wan the magic kilowatt then use two of them
> to get 1200W with each "loafing" at 600W.
>
> The difference dropping from 1500W -> 1200W output is less than 1dB - a
> fraction of an S-point but can make your signal 6-10 times cleaner and
> reduce your electric bill.
>
> I wonder how many people on here run their amplifiers at below the 1dB
> compression point? and without ALC?
>
>
> Mike G8TIC/M0VHF
>
>
>
>
> On 26/07/2012 21:50, David Jordan wrote:
>> Isn't this a really old concern? I remember having an FT-1000D where I
>> noticed that instantaneous spike on key-down.
>>
>> I noticed in the menu of the Kenwood TS-480SAT you can select the
>> response
>> time of the transmit relay. I always thought that was Kenwoods approach
>> to
>> solving this concern?
>>
>> 73,
>> Dave
>> Wa3gin
>>
>> -----Original Message-----
>> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>> Behalf Of Richard Solomon
>> Sent: Thursday, July 26, 2012 4:39 PM
>> To: amps@contesting.com
>> Subject: Re: [Amps] Overdrive protection
>>
>> Not "all" of us know which they are ... is there a list somewhere of
>> those
>> rigs that exhibit this nasty problem ? Maybe if we boycott those rigs
>> then
>> the manufacturer will modify them.
>>
>> 73, Dick, W1KSZ
>>
>> _______________________________________________
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>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
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