On 9/23/2010 9:34 AM, Jim Thomson wrote:
> Date: Thu, 23 Sep 2010 19:58:55 +0800
> From: Alek Petkovic<vk6apk@bigpond.com>
> Subject: Re: [Amps] Pulse tuning
> To: dezrat1242@yahoo.com,amps@contesting.com
> Message-ID:
> <20100923115856.LAIE8424.nschwotgx01p.mx.bigpond.com@MARMION.bigpond.com>
>
> Content-Type: text/plain; charset="us-ascii"; format=flowed
>
> At 07:22 PM 23/09/2010, Bill, W6WRT wrote:
>> ORIGINAL MESSAGE:
>>
>> On Thu, 23 Sep 2010 03:57:11 -0500, donroden@hiwaay.net wrote:
>>
>>> If you have to pulse, you are relying too much on power supply capacitors.
>>> Just build it "large" and don't worry about pulsing.
>>> Don WA4NPL
>> REPLY:
>>
>> I agree. If you HAVE to pulse to avoid damage,
I don't think that is the usual reason for pulse tuning.
Our voices consist of a broad range of frequencies of widely varying
amplitude.
Some one asked what is the duty cycle, 50% 60%..what ever, but without
processing I think the average is figured at roughly 20% to 30%. What
does the FCC use for exposure levels? IIRC it's 20%. Speech processing
can raise this substantially. However I'm not nearly as concerned
about duty cycle as I amp those random high peaks and they are something
that pulse tuning is not likely to simulate.
"usually" pulse tuning is used to approximate the duty cycle of SSB
which should result in an equivalent drop in plate voltage on most peaks
IF it's a good representation of your voice. My voice has a very high
peak to average power and benefits greatly. I get good (un requested)
signal reports running substantial processing when setting up the ALC
and compression according to the manual for the 756 pro. Running the amp
up to the legal limit I've received quite a few complimentary reports
and no splatter.
Many commercial amps are a bit short on capacitance and transformer KVA.
The two together can give a much lower plate voltage than what is seen
in typical SSB operation. Most including those with anemic power
supplies can be tuned full carrier without damage as long as it isn't
over done.
Over the years I've had many amps and the power out (carrier Vs peak on
SSB) has varied from 200 to almost 500 watts.
However it depends on how hard I ran them. My current amp, which has a
lot of overhead at the legal limit shows very little difference between
solid carrier at 1500 out and running 1500 PEP out. I'm sure that would
not be the same were I running the amp full out and no speech
processing. Matter-a-fact the advertised figures show 500 watts
difference between full carrier and PEP at max.
73
Roger (K8RI)
>> you amp is running on the
>> edge of self-destruction anyway. Beef it up so it can run full carrier
>> for at least five minutes at a time with no sweat. Then you can tune it
>> up the 'right' way.
>>
>> Bill, W6WRT
>
>
>
> Surely, with pulse tuning, you are getting the duty cycle as close as
> possible to ssb conditions. Therefore you are tuning your amplifier
> to the absolute optimum level.
>
> When you tune with full carrier, power supply sag come into play in a
> big way and so, once you have tuned your amp under constant carrier
> conditions, it will be less than optimum for ssb operation.
>
> Tell me if I'm barking up the wrong tree but I see pulse tuning as
> the obvious way to go.
>
> 73, Alek.
> VK6APK
>
> ## Myself, and everyone here in town has used pulse tuning since the
> late 70's. Alek is correct. You are better off to use pulse tuning, and
> tweak the
> duty cycle such that it's the same as the mode you will be using. On some of
> these amps, the B+ regulation is crap. Tune with a dead cxr and ur po will
> be way
> less than when on ssb. On ssb ur average B+ will be a lot higher. Tune
> with a cxr,
> and you have NOT tuned up for max pep out, when on ssb.
>
> ## tune with a cxr, and if something is off resonance a bit, then plate
> current is way higher
> than normal, and po is way less than normal. Plate diss is way higher than
> normal. Why beat
> the crap out of the tubes, bandswitch's, plate xfmr, and everything else ?
> If somebody doesn't like
> the string of 60 wpm dots, then they can either QSY...or turn on the auto
> notch. If I'm in a ssb
> round table, and have to tweak the amp, I switch to CW.. and use the
> opposite sideband...so the
> folks in roundatble hear........nothing.
>
> later... Jim VE7RF
>
>
>
>
>
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