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Re: [Amps] Amp output power

Subject: Re: [Amps] Amp output power
From: "Roger (K8RI)" <>
Date: Tue, 25 Aug 2015 02:38:25 -0400
List-post: <">>
The early datasheets showed larger figures than the later ones. Yes, I believe the derating was a political move to make the FCC happy<:-) Just remember when running near maximum ratings and particularly grid ratings on fragile tubes, that tune and load control adjustments are small and careful. A tiny excursion into over drive due to moving the load control too far can quickly destroy a tube. With over drive protection and careful tuning, the tube can be run on the edge and last for years.

It's a good idea to have sensitive and quick acting over drive protection.

For those who call the 3CX800 small, take a look at the 3CX400/8874. Then look at the price. No wonder so many are converted to 3CX800A7s or 3CPX800A7s


Roger  (K8RI)

On 8/24/2015 5:31 PM, Steve Thompson wrote:
If you check at

there's several data sheets. I came across a copy of the one with 1370W output spec. and copied it to David to host. I believe there was a spell where FCC applied rules relating to output power spec. of the devices in a transmitter, hence the 750W rating appearing so a pair was valid for a 1500W amplifier.

I think the same applied in the case of Svetlana 4CX800A data.


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On Sun, 23 Aug 2015 18:25:38 -0700, Jim wrote:

The non-pulse rated 3cx800 max ratings are 2250V plate voltage, 0.6
plate amps. Typical operation at 2200V and 0.5A with 23W of drive will
get you 750W AB2 output.


That's interesting. At 2250 VDC and .6 amps, the DC input is only 1350
watts. At 60% efficiency, the RF output would be 810 watts and the
plate dissipation would be 540 watts.

The tube's rated plate dissipation is 800 watts, yet in class AB with
max Vp and Ip, you come nowhere near that rating. Most tubes will put
out RF well in excess of their dissipation rating. For example, a
3-500Z with only 500 watts plate dissipation will put out 750 watts
and still be within ratings.

The question is, why would a tube have such a high dissipation rating
if it is not capable of reaching that in normal class AB operation?
Perhaps it is intended for use in class A?

Seems strange to me. Your thoughts?

73, Bill W6WRT

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