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

To: "Larry" <>, "Joe Subich, W4TV" <>
Subject: Re: [Amps] How to read the 3-500Z spec sheet?
From: "Carl" <>
Date: Sun, 23 May 2010 17:20:26 -0400
List-post: <">>

> 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

Amen to that last paragraph. A pair of 4-400's will run for many years in 
BCB 24/7 service at 1000-1200W out. Thats carrier power, the PEP is 

The 813 is my favorite for the most underated of the old time popular tubes. 
I regularly run them in AM service at a measured 210W dissipation at the 
carrier level and the graphite anodes barely show color on voice peaks. Just 
a muffin fan running at reduced voltage to move some air around.

The problem with running over 2500V on a 3-500Z is that the IMD increases 
rapidly unless you apply NFB.

Which Henry's run 4KV on 3-500's? Those Im familiar with are well under 3KV 
unless the choke is removed.


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