[Amps] 1 db compression point procedure ?

[Carl]

It is useful to tell what your amp tubes are really capable of.

For example a pair of 572B's will start compressing at 75-80W altho they are 
rated at 50W drive each. OTOH a pair of 3-500's wont be compressing at 100W 
but those driving a single tube 3-500 amp will be all over the band at that 
power.

At 100W the much maligned Clipperton L is a very clean amp, at 200W it is 
dirty until the plate xfmr melts down.

Carl
KM1H


----- Original Message ----- 
From: "Gary Schafer" <garyschafer at comcast.net>
To: "'Jim Thomson'" <jim.thom at telus.net>; <amps at contesting.com>
Sent: Thursday, July 01, 2010 9:20 PM
Subject: Re: [Amps] 1 db compression point procedure ?


> The 1 db compression point is usually concerned with input power to an
> amplifier. Usually a receiver front end or preamp.
> You usually want to know how big of an input signal the amp will handle
> before compression starts. The 1 db figure is a  common reference point 
> for
> amplifier comparison. Those amplifiers are class A very linear amplifiers.
>
> Our typical ham power amplifiers have nowhere that kind of linearity. If 
> you
> were to plot output verses input on most amps you will find that it swings
> around quite a bit as drive is increased. Compression at the  high end can
> be a surprising amount.
>
> 73
> Gary K4FMX
>
>
>> -----Original Message-----
>> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
>> Behalf Of Jim Thomson
>> Sent: Wednesday, June 30, 2010 7:40 AM
>> To: amps at contesting.com
>> Subject: [Amps] 1 db compression point procedure ?
>>
>> Ok
>>
>> What's the exact procedure for finding the ..'1db compression point'   on
>> a HF amp ??
>>
>> I have conflicting info on the procedure.   With hardly any drive, the 
>> typ
>> HF amp has a
>> lot of gain.    As drive levels increase, the gain goes down.   Question
>> is.... where is the
>> starting point of all this??     With 1 watt of drive... or 5w or what ?
>> It makes a big diff
>> to the results.
>>
>> I'm assuming the amp is 1st tuned to  say normal power output... like
>> 1200-1500w out..
>> IE: tune and load tweaked for max power out at normal power, then maybe
>> increase the
>> loading a tiny bit  [ slightly more Un meshed].
>>
>> Then leave the tune and load caps alone... and reduce drive to a very
>> small amount... and   then measure
>> both the drive to the amp... and also the power output of the amp  [ say
>> 1-5 w of drive.. and  20-100w out]
>>   Then start increasing drive level a bit  and  measure the gain once 
>> more
>> [ it should be dropping off a bit]
>>
>> Does this procedure have to be done with a cxr.. or can we do it pulse
>> tuned ??    Have I even got the
>> procedure any where near correct??
>>
>> I take it, we don't want to operate the amp beyond the point  where the
>> gain drops by 1 db ?    But
>> where is the starting point ?
>>
>> I can also tweak the bias on the GG amp quite a bit.
>>
>> tnx.... Jim   VE7RF
>>
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