[Milsurplus] Navy MAK and the HY1269

[Kenneth G. Gordon]

On 24 May 2019 at 14:18, Ray Fantini wrote:

>     The transmitter is a four channel crystal control using a 12A6 as the oscillator that drives a 
>     HY1269 PA tube, that tube is plate modulated y two more HY1269 tubes in parallel.
>     This is my first exposure to the HY1269 tube and it appears to me to be a quick heating power 
>     pentode rated at 30 watts, 750 volts max DC plate at a max current of 120 MA.

True, but notice that the filament voltage is specified at 6.0 V/12.0 V, and NOT 6.3 or 12.6. 

In fact, in the tube data sheet it specifically mentions that the filament connections must be 
made with small wire in order to introduce the necessary 0.3 volt drop at 6.0 V.

Secondly, it also makes mention that no voltages should be applied to the tube ahead of the 
application of filament voltage. They must either be applied simultaneously, or the filament 
must be lit first.

Thirdly, the filament is a thoriated tungsten type, and normally glows at a very bright white 
color. If the tube is wired for 12 V rather than 6 V filament source, I think you should 
measure that voltage AT the filament pins, make sure it is 12.0 V, then don't worry about the 
color or brightness.

The specs say that the tube is designed for "quick heating" and also says that it may be 
completely turned off when receiving because it comes up to temperature so quickly.

Lastly, the specs show that for plate-and-screen modulated Class C operation, plate voltage 
should be 600 VDC for 42 watts output, but for 29 watts output (close enough to the military 
spec of 30 watts), plate voltage should be 500 VDC.

If that was my rig, I'd use no more than 500 VDC for plate voltage, and maybe I'd drop it 
towards 400 VDC. At 400 VDC, the specs say that output would be 22.5 watts.

It looks to me to be a very interesting tube and I think that the MAK is also a very interesting 
rig.

Please do keep us informed of your progress with it.

Ken W7EKB