I agree.
Don WA4NPL
Quoting "Gary Schafer" <garyschafer@comcast.net>:
> Everyone seems to be using different terms in this discussion so no one
> agrees. Most are saying the right thing but referring to the wrong thing.
>
> First, as to the SSB amplifier being tuned properly at only ONE power level,
> that is true and not true, depending what you are looking at.
>
> As far as efficiency goes it is true. When you tune the amp for maximum
> output at a given drive level for SSB operation you are setting the tank
> load impedance to match the tube impedance ONLY at the maximum power output
> point.
> As you reduce drive without changing the load network tuning the power
> output drops and the efficiency drops too. The circuit is at maximum
> efficiency at only the ONE power level.
>
> So how does this work with voice on SSB where the power level is constantly
> changing?
> We don't really care that the efficiency is not the same at lower voice
> levels as it is at maximum level.
> The thing we care about is the linearity in the output with respect to
> drive. In other words if our amp has a gain of 10 db at maximum output level
> we still want it to have a gain of 10 db at low output levels too. If we
> drive it with 100 watts and get 1000 out then when we drive it with 10 watts
> we should get 100 watts out. 1 watt of drive should give 10 watts out.
> Always 10 db of gain.
>
> But the input power of the amplifier is NOT linear with respect to drive
> power or output power. As an example at maximum power output say it has 60%
> efficiency. For 1000 watts out it would have to run 1666 watts input. At 250
> watts out the efficiency will be 1/2 that or 30%. So to get 250 watts out it
> would take 833 watts input. We have dropped the input power in half but the
> output power has dropped to 1/4. We have not touched any tuning controls. We
> have only reduced drive to 1/4 of what it took to produce 1000 watts output.
>
> Is the amplifier then mis-tuned at all power levels but the maximum power
> level? NO it is not.
>
> Is there a mismatch in the tube plate load impedance and the tank network
> impedance at lower voice power levels from what it is at maximum power
> levels?
> YES there is! But that is the way it must operate in order for the amplifier
> to remain linear between input drive and output power.
>
> REDUCING POWER OUT FOR CW OR RTTY:
>
> Let's say that we only want to run the above amplifier at 250 watts output
> for RTTY. We can simply apply our 100 watts of drive and tune the amp for
> maximum output of 1000 watts and then reduce the drive to 25 watts and it
> should produce 250 watts output. But our efficiency will now be 30% rather
> than 60% that it achieves at 1000 watts out. With 250 watts out the input
> power will be 833 watts.
>
> If we retune the output network for maximum output to get our efficiency
> back up to 60% at 250 watts output, our input power will drop down to 416
> watts.
>
> TANK CIRCUIT STRESS:
> Leaving plate voltage the same.
>
> If we retune for maximum output and efficiency at the lower power output
> (250 watts), we are now matching a much higher plate load impedance than
> before. Less plate current same plate voltage.
> We have stepped up the impedance of the input of the tank circuit by
> retuning its capacitors to match the new plate load impedance presented by
> the tube rather than leaving it at the mismatched load impedance when we
> first reduced power from 1000 watts.
>
> Since we are not changing the tank inductance the tank Q will be increased.
> Increased tank Q means higher circulating currents in all components and
> greater phase shift across the tank coil providing for higher voltages
> across it and the band switch.
>
> BUT we are now operating at a lower power level than the original 1000 watts
> power output that the amp was designed for so all currents and voltages will
> be lower than at the 1000 watt level. How much lower, I haven't done the
> math to see if the increased tank Q will bring them back up to as high or
> higher than operating at the 1000 watt level. Someone may want to do that
> for comparison. It shouldn't be too hard with the on line calculators.
>
> Dropping plate voltage and plate current to maintain the same load impedance
> at lower power as at full power will maintain the same tank Q which would be
> the most desirable. Then all currents and voltages in the tank will be sure
> to be lower.
>
> 73
> Gary K4FMX
>
>> -----Original Message-----
>> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>> Behalf Of Joe Subich, W4TV
>> Sent: Saturday, August 29, 2009 11:18 PM
>> To: 'jerome schatten'
>> Cc: amps@contesting.com
>> Subject: Re: [Amps] SB-220 bias question
>>
>>
>>
>> > If the amplifier was then used on SSB driven by a human
>> > voice, the only time the amp would _not_ be mis-tuned is
>> > when the human voice peak drove the amp to exactly the
>> > same level as the peak of the tone used for tun-up.
>> >
>> > That seems wacky to me.
>>
>> No ... with SSB the plate load impedance is dynamic as
>> opposed to static (a single value) with CW or RTTY. For
>> SSB or any other amplitude modulated emission, the
>> calculation of plate load impedance includes the plate
>> conduction angle and average (dynamic) Ep/Ip ratio.
>>
>> The tank (flywheel) effect of the output network smoothes
>> the impedance swings.
>>
>> With On/Off keying or FSK, Ep/Ip is constant there is no
>> dynamic variation.
>>
>>
>> > -----Original Message-----
>> > From: jerome schatten [mailto:romers@shaw.ca]
>> > Sent: Saturday, August 29, 2009 9:33 PM
>> > To: Gudguyham@aol.com; lists@subich.com; sub1@rogerhalstead.com
>> > Cc: amps@contesting.com
>> > Subject: Re: [Amps] SB-220 bias question
>> >
>> >
>> > And by extension, consider an amplifier tuned with a steady tone for
>> > maximum power out when the i/p side of the pi network matches
>> > the tube
>> > plate Z and the output of the pi matches the load Z. If the
>> > amplifier
>> > was then used on SSB driven by a human voice, the only time the amp
>> > would _not_ be mis-tuned is when the human voice peak drove
>> > the amp to
>> > exactly the same level as the peak of the tone used for tun-up.
>> >
>> > That seems wacky to me.
>> >
>> > jerome - va7vv
>> >
>> > On Sat, 29 Aug 2009 17:56:36 -0700, <Gudguyham@aol.com> wrote:
>> >
>> > >
>> >
>> > >
>> > > Fine, but none of those amps change the plate voltage in the
>> > > different
>> > > modes, so you mean to tell me they are designed wrong?
>> > >
>> >
>>
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>
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