[Amps] Overdrive protection

[Jim Barber]

I don't see what's controversial about and of that, just common sense.

I think the problem is more that people who are thoughtful about the
way they operate only occasionally need ALC and other protection devices.
I'm as block-headed as a lot of others, but I run 20W PEP into the tetrodes
and just a little more than that into the larger ceramic triodes and it
works well. Of course I'm not attracted to "dogpile" DX'ing, where the
loudest, nastiest signal often wins. All that RF compression can be useful
if you don't care about hygiene. How many 8877's are run at 2500++ out and
into hard compression during contests? If you put ALC on those guy's rigs
they'd swear something was broken and pull the cable off anyway, right
before they posted complaints about excessive tube and component
failures...

73,
Jim N7CXI

On 7/26/2012 2:47 PM, Mike Tubby wrote:
> 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 at contesting.com [mailto:amps-bounces at contesting.com] On
>> Behalf Of Richard Solomon
>> Sent: Thursday, July 26, 2012 4:39 PM
>> To: amps at 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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