AL-80A/B Do people really get 1kw output?

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Michael Waldrop:
According to Ameritron's website, the AL-80B amplifier
is designed to produce "UP TO 1KW PEP" output.


I talked with application engineering at Eimac back in the 90's when Ameritron was using Eimac tubes.  According to Eimac, if anyone is driving a single 3-500z or zg to 1kw out, then they are exceeding Eimacs absolute ratings for that tube. Period.  Also, Eimac z or zg versions of the 3-500 have exactly the same maximum absolute ratings. Also Period.  Other manufacturers can make up their own ratings.


All I ever seen on the AL-80A and the AL-80B I used to own, was 800 watts CW measured by a Palstar watt meter.  Could very well be 1KW PEP?  If I had a Bird PEP reading meter perhaps it would show different. The volt and plate meter on the amps support the 800 watts given 60% efficiency.  Driving any amplifier to the last watt which usually means light loading, cause non-linearity and splatter.  The AL-80 A&B are nice amps.  Run them at 600 to 800 watts SSB, they’ll last for ever. On the other guy's S meter it will look like you are running 1000!

Lon Kinley:
WB4JZY - Another call sign that's not in the FCC database as of this date.


Lon - W3LK
Naugatuck, Connecticut

Tom Rauch:
Some people are giving authoritative answers, but they obviously don't understand tube operation or heat or other issues related to power grid tubes.

What they have most likely done is grabbed something from a typical operation chart and assumed there is only one set of operating conditions for tube operation.

The 1000 w PEP out is the IVS (Intermittent voice service) operation rating of the tube. The amp is rated at about 800 watts out on CW carrier, and the manual says to not go over 400mA on CW carrier. That's because on CW the average plate current can be as high as 400mA for rated heat limits. The anode dissipation (heat) is based on Pin - Pout (Pout has to be adjusted to not include any external losses like tank losses, since they do not heat the tube). So at about 400mA and about 800W output the anode dissipation will be 400 watts or less.

At a short term average anode current (which is what the meter shows) of 400mA, the peak cathode current will be 1.6amps. All of which is perfectly safe for the 3-500Z.

On voice the average anode current will be about 200-300mA at 1000W PEP output, and average output would be 200-500 watts depending on processing and audio waveshape. The instantaneous peak emission current would be about 1.9 amps, which is still well within peak emission limits. So the dissipation would be 300 watts or less typically on voice. Perfectly safe.

The tube won't have shorter life or any other noticeable problem when operated at 1000W or even more PEP on voice, and IMD is quite acceptable at 1000W PEP. It measured about -33dB one tone of two equal tones, which is -39dB PEP. Most radios are only around -30 or -35 below PEP, so the amp won't substantially change the IM performance at 1kW PEP when properly tuned.

As a matter of fact as long as we don't overheat the elements in a thoriated tungsten tube to the point of physical damage there is no life shortening at all due to excessive emission current. So what people are pulling out of their rear pockets is simply not accurate. They are probably just inventing it without actual experience or science.

By the way, this is NOT true for metal oxide cathodes. A metal oxide cathode can be stripped from excessive HV or excessive cathode current (or low cathode temperature operation), but a thoriated tungsten emitter like the 3-500Z is immune to that. A tube like the 3-500Z wears out from net filament hours at a certain filament voltage, not emission hours at a certain cathode emission. It also is not damaged by the AMOUNT of emission demand, unlike the oxide cathode that is quickly destroyed by excessive emission demand.

As a matter of fact Eimac in Salt Lake was aware of and approved the IVS operation of that amp. They always gave full warranty on tubes when operated as rated in the manual. Amperex did the same, also based on IVS service for voice and ICAS for CW.

The FCC approved the amps under that rating, Eimac had no problems, and Amperex also looked at and approved the operation. IMD was tested at that level, and anyone who knows anything at all about thoriated tungsten tubes or even general tube operation would understand the difference between CCS carrier (at 400mA) and PEP voice operation.

73 Tom


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