Hi Rex,
It varies from 50% at idle to about 90% max, depending on data content.
Source KK7UQ: http://kk7uq.com/html/download/IMD%2520Presentation.ppt
He's the guy who came up with that nifty IMD meter hardware gadget.
73/jeff/ac0c
Rex Lint wrote:
> I would think that PSK would be the same as RTTY - you have a tone on all
> the time - just changing its phase
>
> -Rex-
>
> K1HI
> Rex Lint
> Merrimack, NH
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Jeff Blaine
> Sent: Thursday, March 12, 2009 3:17 AM
> To: jtml@vla.com
> Cc: amps@contesting.com
> Subject: Re: [Amps] plate dissipation and duty factor
>
> Hi John,
>
> Thanks very much for the info. That's a great bit of data there. And
> it's great to have that confirmation.
>
> For the duty cycle, the ARRL if I remember correctly calls out the duty
> cycles for unprocessed SSB at 20%, and processed SSB as well as
> "conversational" CW both at 40%. And I want to say that PSK runs about
> 70% - something like that.
>
> So to combine all this together, let's say that we have a CCS plate dis
> spec of 100W. And assuming the scaling effect (duty cycle vs plate dis)
> is completely linear, then that means we should be able to safely run at
> these power levels - assuming here that we are only talking about the
> tube to simplify the discussion:
>
> Mode duty cycle plate dis
> --------------------------------------------
> RTTY 100% 100w
> PSK (approx) 70% 140w
> Unprocessed SSB 20% 500w
> Processed SSB/CW 40% 250w
>
> What do you think?
>
> 73/jeff/ac0c
>
>
>
> John Lyles wrote:
>
>> You are correct that RTTY is basically 100% on like FM, at least during a
>>
> burst of transmission. So this is limited by the average plate dissipation
> of the tube, not to exceed XXX watts or KW. Thermally, a few seconds on is
> like CW as far as the tube anode structure is concerned.
>
>> For pulsed ratings, the average dissipation limit is the same. If you are
>>
> on 10% of the time, then the peak power may go up to the limits of the
> cathode emission current of the tube in some cases, however, the plate
> dissipation still sets the limit for the thermal loading on the anode. If
> you run 10 X the CW power level and are on 10% of the time, its the same
> dissipation as CW. You cannot cheat and get more dissipation on an average
> than the tube is capable of. You can get high peak dissipation, but that
> really isn't the definition of dissipation. Its an average thing. There is a
> limit to how long you can leave the pulse on, however, before the tube
> makers say no. In other words, you cannot run, like 1 second on at 10 X the
> average dissipation, then wait 10 seconds and do it again, and expect long
> life. Fusion RF systems run a blast of RF for 20-100 seconds, and they are
> considered CW. Particle accelerators like where I work run 10% DF, so we can
> crank up the peak to quite
> h
>
>> igh. We
>> have 250 kW of plate dissipation in triodes, and on a peak basis its like
>>
> 2.5 MW. But thermally it is only 250 kW of power into the copper. The pulses
> are short.
>
>> Oxide cathode and thoriated tungsten tubes have their favored regimes with
>>
> respect to peak cathode emission, which is often another unmentioned limit
> of a tube.
>
>> As for SSB, I defer to those who practice making SSB amplifiers.
>>
>> 73
>> John
>> K5PRO
>>
>>
>>
>>> Message: 7
>>> Date: Wed, 11 Mar 2009 21:51:34 -0500
>>> From: Jeff Blaine <keepwalking188@yahoo.com>
>>> Subject: [Amps] What is the true and actual meaning of a plate
>>> dissipation limit?
>>>
>>> Gentlemen,
>>>
>>> Wanted: an understanding of the actual and true meaning of the plate
>>> disipation limits with respect to duty cycle.
>>>
>>> I may have missed it, but it seems the answer is hiding at least from me.
>>>
>>> All our tubes have plate dis limits associated with them. Sometimes
>>> there is an associated cooling requirement with it as a footnote, but
>>> beyond that, not much else is said.
>>>
>>> Say a guy loves SSB (low duty cycle) and RTTY (100% duty cycle). The
>>> rule of thumb in some cases is to run the RTTY mode at 1/2 the typical
>>> power of SSB. But this is often stated without explaining why the RTTY
>>> power level specified as 1/2 is the right level from a specification or
>>> design standpoint.
>>>
>>> I realize that in the greater scheme, there are a host of components to
>>> consider when talking about an amp as a whole. But here i am addressing
>>> the tube only as an isolated case.
>>>
>>> Eimac's C&F does not mention RTTY that I recll, but they do talk a lot
>>> about commercial 24/7 FM service - and that's a 100% non-stop mode;
>>> equivalent to RTTY. They suggest in the C&F documents that the tube
>>> will run up to the rated plate dis in CCS. OK. Maybe the
>>> interpretation is that the Pd-max is a hard limit? Valid for all time
>>> and all cases.
>>>
>>> And then there are the pulse applications that come along and spoil the
>>> CCS argument. Many tubes have a pulse rating - or in the case of many
>>> of the Russian tubes - a pulse rating spec set only without CCS duty
>>> being adequately specified.
>>>
>>> In these pulse duty cases, the time averaged plate dis is below the
>>> published limit, I'm sure. But for the pulse duration, the Pd is going
>>> to be exceeded by a huge margin.
>>>
>>> That means, that in some lower duty cycle circumstances, the assumed CCS
>>> Pd can be safely exceeded.
>>>
>>> However I cannot find an explanation that ties the duty cycle to the
>>> plate dissipation. Reconciling the two data points. Either on a
>>> derating or pulse basis - even as a rule-of-thumb kind of factor.
>>>
>>> The usual sources are not clear on the point. The Eimac literature does
>>> not come out and say it clearly. Bill Orr loves heavy metal for
>>> transformers - but for SSB duty, has no problems exceeding the CCS specs
>>> on many components including tubes. And nothing on the net that I've
>>> seen links a position and some data or logic into something that is more
>>> substantial that would pull it out of the opinion and into the
>>> engineering basis category.
>>>
>>> Hoping that one of you guys working in the industry - or having
>>> encountered this question before - may have the magic answer that hooks
>>> the plate dis and duty cycle together...
>>>
>>> 73/jeff/ac0c
>>>
>>>
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