Low input tube amps

[Mudfoot]

Are there any decent, worthwhile tube amps that deliver full output with 5 ish watts input?

Something that does in excess of 300 watts and doesn't require rare exotic tubes?

At least 80-10 meters.

 

[Dmans]

Yes.
The Unicorn 1000.

73
David

 

[groundwire]

With that kind of drive your stuck with sweep tubes for the most part.

 

[543_Dallas]

Use a driver or build something with a tetrode. The fcc limit of 15 db gain (or whatever it is) limits your options with store bought stuff. Some tetrodes like the 250b are not known for the best IMD. I'm sure someone could explain why and how to correct it, but I'm not that guy.

 

[kopcicle]

find a grid driven circuit

 

[BJ radionut]

I am thinking Alpha or Commander with single 3cx800...most guys that run those say 25 watts drive will equal around a kw
So not sure where you would be with 5-10 watts

 

[Mudfoot]

I am thinking Alpha or Commander with single 3cx800...most guys that run those say 25 watts drive will equal around a kw
So not sure where you would be with 5-10 watts

Didn't Johnson make something low drive?

 

[BJ radionut]

http://www.hampedia.net/power_amplifiers/efjohnson/thunderbolt.php

 

[Mudfoot]

That's it.

 

[BJ radionut]

https://swap.qth.com/view_photo.php?counter=1478888

 

[543_Dallas]

I didn't even think about the 3cx800. An 8877 has similar gain. Unfortunately 5 watts in would only get you around 150 out. Either would be a waste of an expensive tube with 5 to 10 watts of drive.

Grid driven will get you more gain. The smart guy that can tame the dirty tetrode will have to help with that one also.

 

[nomadradio]

require rare exotic tubes?

These days seems like all tubes are both rare and exotic.

The power level in question would call for multiple small tubes, or one larger one.

Pride DX300 falls in this category.

Not cheap.

73

 

[BJ radionut]

Driving powers of as little as 5 W will produce a respectable amount of RF output from this amplifier. ARRL Lab measurements show this amplifier - operating at 14.2 MHz - will produce RF power output levels of 220, 440, 575, and 700 W for driving powers of 5, 10, 15, and 20 W, respectively. Like the sound of that?

A low-drive, grounded-grid 3CX800A7 amplifier

https://www.robkalmeijer.nl/technie...hniek/hambladen/qst/1988/07/page22/index.html

 

[Mudfoot]

I recall that

 

[nomadradio]

I put two 3CX800s in a Dentron MLA2500 20 years ago. My D201 would drive it to about 800 Watts PEP. A radio with 100W PEP would naturally hit it a lot harder.

But this was done by using a tuned input to the cathodes of the tubes.

The Dentron's original method of losing half the drive power in a resistor would not get you quite that much power gain.

73