[Amps] Ameritron AL-800

[Paul Decker]

I'm not sure. I see at 450 MHz it is 46% efficiency

But typical operation at 150 MHz is listed as:

3CX800A7 – Typical Operation (Measured Data to 150 MHz)

Class AB2, Cathode Driven

Parameter	Value
Plate Voltage	2200 Vdc
Cathode Bias Voltage	+8.2 Vdc
Zero-Signal Plate Current	150 mAdc
CW Plate Current	500 mAdc
CW Power Input	1100 W
Peak Envelope Power Input	1100 W
Two-Tone Plate Current	313 mAdc
CW Grid Current	16 mAdc
Two-Tone Grid Current	16 mAdc
Peak RF Cathode Voltage	64 V
Peak Driving Power	70 W
Useful Power Output (CW)	750 W
Useful Power Output, PEP	**1100 W
Cathode Input Impedance	54 Ohms
Resonant Load Impedance	2700 Ohms
Intermodulation Distortion (IMD)	
– 3rd Order Products	–36 dB
– 5th Order Products	–32 dB

> On 12/10/2025 7:01 PM EST Douglas L <sparks06524 at yahoo.com> wrote:
> 
>  
> Checking the specs, the 3CX800U7 is rated at 350 watts output with an efficiency of only 33%. That’s less than half the rated output power of the 3CX800A7.
> I wonder if it was derated for typical UHF service?
> If not, it’s a poor substitute for a 3CX800A7.
> Doug/WA1TUT
> 
> 
> > On Dec 10, 2025, at 1:01 PM, Paul Decker via Amps <amps at contesting.com> wrote:
> > 
> > 
> >> 
> >>> Has anyone created a work around to replace the 3CX800A7 tubes in the
> >>> AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
> > 
> > The 3cx400U7 and 3cx800U7 are usually much cheaper alternatives and in many cases can be NOS. The datasheet lists the working B+ as lower, but I suspect that is simply due to the higher frequency rating of the U7
> > 
> > The only issue is changing out the base which seems daunting at first. There is an "RCA like" plug connector that fits the base really well so that only the grid ring needs to be figured out with some simple finger stock and a metal plate.
> > 
> > Someone with talent could design an adapter board that would work well too!
> > 
> > Paul
> > KG7HF
> > 
> > _______________________________________________
> > Amps mailing list
> > Amps at contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps