[Amps] How to read the 3-500Z spec sheet?

Sun May 23 17:11:26 PDT 2010

> On the other hand if you are running high duty cycle modes (e.g.
> FM or plate modulated AM) the recommendations are lower - as low
> as 275 mA for plate modulated AM.

That is carrier power only Joe. PEP is 4X the carrier on AM

Carl
KM1H

----- Original Message ----- 
From: "Joe Subich, W4TV" <lists at subich.com>
To: "Larry" <larry at w7iuv.com>
Cc: <Amps at contesting.com>
Sent: Sunday, May 23, 2010 6:49 PM
Subject: Re: [Amps] How to read the 3-500Z spec sheet?

>
>
> > Wrong again Joe. Joe, K1JT, has real insight into this area. He has
> > programmed the DSP in the soundcard tone generator to produce a
> > smooth phase transistion between one tone and the next.
>
> I don't care what kind of transition Joe has programmed into the
> DSP.  The rise time/wave shaping makes little difference with a
> class C amplifier because the sharp turn on/turn off characteristic
> and saturated operation will always square up the pulses.
>
> A Class C amplifier requires a certain level of drive to "turn on"
> and operates in saturation ... the turn on threshold will remove
> much of the low level ramp up and the saturation will create sharp
> "corners" at the top of each pulse.  Even the most basic measurement
> with a dual trace oscilloscope will show the difference between a
> linear amplifier and one run in class C.  Run a string of dits
> through a class C amplifier and compare the difference between
> the drive signal and the output.
>
> > The result is complete freedom from the type of clicks you hear
> > when your receiver noise blanker is driven nuts by the strong
> > RTTY signal 200 Hz off your frequency.
>
> The clicks are not receiver generated ... they are generated in
> the transmitter/amplifier by pulse squaring and eliminating the
> wave shaping created in the exciter.  W7AY has done extensive
> work with wave shaping and can show the "damage" caused by non-
> linear amplifiers in FSK and AFSK systems.
>
> > Last I looked Duty Cycle was defined by the ratio between ON time and
> > OFF time. No time limit specified.
>
> Any calculation of "duty cycle" must include a time limit ...
> otherwise even full carrier AM can have an extremely small
> duty cycle if the transmission period is short compared to
> the measurement period.
>
> Simply put, when one limits the calculation to transmission
> periods, AM, FSK/AFSK, WSJT, etc. are 100% duty cycle modes.
> CW is a 50% - 60% duty cycle mode (depending on message
> content) and SSB is up to 60% (depending on compression or
> clipping levels).  If you start adding "receive time" all
> of those numbers will decrease but it still does not eliminate
> the fact that AM/RTTY/WSJT/etc. are as much as four times as
> taxing on an amplifier than CW at a similar peak power level.
>
> > I won't run mine over 350, just like the "recommended" operation
> > in the tube specs.
>
> Good for you ... however, the Eimac data sheets clearly show 400 mA
> single tone (CW) plate current in AB2 service at all plate voltages
> from 1500 - 3500 (http://www.g8wrb.org/data/Eimac/3-500Z.pdf).
>
> On the other hand if you are running high duty cycle modes (e.g.
> FM or plate modulated AM) the recommendations are lower - as low
> as 275 mA for plate modulated AM.
>
> 73,
>
>    ... Joe, W4TV
>
> On 5/23/2010 4:49 PM, Larry wrote:
>>
>> On 23-May-10 12:42 PM, Joe Subich, W4TV wrote:
>>>
>>> WSJT may be one tone at a time but that still does not eliminate the
>>> need for reasonable linearity unless one wants to generate "clicks"
>>> every time the tone shifts. With class C any attack/decay is made
>>> much more sharp ... you can even hear it on CW with a class C amplifier.
>>
>> Wrong again Joe. Joe, K1JT, has real insight into this area. He has
>> programmed the DSP in the soundcard tone generator to produce a smooth
>> phase transistion between one tone and the next. The result is complete
>> freedom from the type of clicks you hear when your receiver noise
>> blanker is driven nuts by the strong RTTY signal 200 Hz off your
>> frequency. If you don't believe me, go ask Joe. He will most likely be
>> happy to point you to the documentation.
>>
>>>
>>> > I have run a SB-220 converted for 6 on EME at 800 watts output (CW
>>> > position). It worked OK as long as I operated it with the outside
>>> > cabinet removed.
>>>
>>> Since that was two tubes, I suspect (hope) you were staying under
>>> 800 mA (400 mA per tube) - you should have been able to reach 800W
>>> out with two tubes although running on the high tap would have
>>> been easier.
>>
>> 2x3-500Z will run 1500 watts output on HF (and probably 6 mtrs) carrier
>> 100% duty cycle for a very very long time (years) IF you run the HV high
>> enough to keep the anode current below 350 ma. per tube. And run lots of
>> air past the seals in the manufacturer approved manner (no like SB-220)
>> At least you can with Eimac and Amperex, no telling what you might get
>> from the chinese tubes.
>>>
>>> > BTW, WSJT JT65 modes as used for EME are true 40% duty cycle, IE 48
>>> > second out of every 2 minutes full carrier power followed by 72
>>> > seconds of standby and/or RX.
>>>
>>> They may be 48% duty cycle on a long term average but they're
>>> 100% duty cycle while transmitting ... and as bad/hard on the
>>> amplifier as RTTY contesting. They're not 50% duty cycle while
>>> transmitting (like CW) or even less like moderately clipped SSB.
>>
>>
>> Last I looked Duty Cycle was defined by the ratio between ON time and
>> OFF time. No time limit specified. CW is not "real" 50% duty cycle
>> unless you are broadcasting 24/7. One minute of TX at 50% and one minute
>> of RX is more like 25% duty cycle, probably less. When I design my amps,
>> they are for real 100% duty cycle. I can take 15 or 20 minutes to tune
>> them up without resorting to any stupid pulser crap or test dummy loads
>> if I want, they don't care. If they break, it's because I screwed up
>> someplace and that only means I need to fix the weak areas.
>>
>>>
>>> I still would not push a single 3-500Z past 400 mA "DC" plate
>>> current and would replace the SB-200 transformer with an AL-80
>>> transformer (with additional filter caps) if it were my amp.
>>
>> I won't run mine over 350, just like the "recommended" operation in the
>> tube specs. I guess some folks just like to buy tubes.....
>>
>> Antique tubes like 4-400A, 813 and 4CX250 can be pushed way above normal
>> ratings if you know what you're doing. Modern junk like 3-500Z and 8877,
>> well just look at how many people on this reflector are always looking
>> for new tubes to replace the ones that mysteriously went bad.
>>
>> 73, Larry
>>
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