Hagenuk HA5K39a with Feldhell Mode.


This is my new German radio. I purchased this radio in oktober 2023, by an exchangement with another radio.

The Hagenuk HA65K39a is a German navy transmiter receiver, which is used on small navy ships or at a naval base on mainland.

It has a seperate receiverpart and a seperate transmitterpart. The receiver is a TRF receiver with only one HF stage, a regenerative detector and one LF stage. All tube types RV12P2000 . The transmitter is a two stage transmitter, with a RL12P10 as a final amplifier. One modulation stage, also acting as a tone oscillator for MCW and sidetone for CW. Tubes are RV12P2000. A stabililizer tube for 150 volt. GR150A.

Provision has been made to tune in the transmitterfrequency to the receiverfrequency.

The modes are phone, CW en MCW. Power is 8 watts on phone and 10 watts on CW

Below the Hagenuk HA5K39a.

Left the receiver and at the rig.ht the transmitter

Below the powersupplies for 300, 200, -50 and 10 volts DC. Also for 12 volts AC. The 200 volts DC is stabilised with a EL84 tube.

Plans were made to make the radio suitable for Feldhell Mode. Normally the a version is not suitable for Feldhell Mode, the versions b and c do.

So I had to make a small change in the internal transmitter part.

The picture below is the change in the schematic diagram.

The main changes in my A version to be done, is to be seen in the diagram up, is:

1 – Desolder the kathode connection to earth.

2 – After disconnecting one of the telephone connection at the front, Solder a wire from the kathode of the PA tube to that disconnected telephone connection. This connection is to be used for the drum contacts of the Hellschreiber. So from the Hell connection on the wsitchbox two wires to that the disconnected telephone entree.

3 – Make a switchbox with a switch for bypassing the CW key connector. Make 2 wires from the normally open contact of the witch to the key input on the front. Switch contacts closed >>> transmit, switch contacts open >>> receive.

4 Switch (Betriebschalter) the mode on the HA5 to CW.

Now the HA5K39 a is suitable for Hellmode. It is a kind of kathode keying of the transmitter poweramplifier by the Hellschreiber drumcontacts, just in the same way, done in the B or C type version of a HA5K39. And it is safe. The contacts of the drum must not exceed 100mA or 150 volts DC. Better some less. So the current now at key down, is about 55 mA at a voltage of 0 volts (kathode keys to earth).

Picture below the front of the Hellschreiber with the connection panel. The big connector is is a homemade one with two contactstifts, to pin 3 and 4 of the Hellschreiber.

Picture below the front panel on the HA5K39. The connector is a homemade type, not done by myself. Also the switchbox with the switch for transmit or receive. Below the connection to the drum contacts of the hellschreiber.

Picure below some received text on the paperstroke of the Hellschreiber. A qso with PA0AOB, Arthur, PA0KDF, Koos.

Below my first test transmission in Hellmode with the HA5K39. A screen of decoded Hell text .BY the PC programm of IZ8BLY. Monitored myself at the websdr of Maasbree. Beautiful thin charactors. That means that the 900 Hz pulses are very well.

Below picture is a reception of my Hell Mode signal from Helge Fykse, LA6NCA in Larvik Norway. That was at 15:00 hr GMT with increased propagation, during the Hell net. My transmitter was the Hagenuk HA5k39 a with 10 watts. Ofcourse I used the Hellschreiber too.

I was a bit proud of it. My report was 456 rst. Not bad at all. Distance about 900 km straight on. Also Arthur, PA0AOB had a good signal.

Ofcourse lateron there appeared some troubles. But I fixed it all. One was, that the frequency of the transmitter drifted quit a lot. About 400 to 600 Hz. That is to much for Hellmode.

And why?

The problem with radio tubes in free running oscillator stages, is the the warming up of the tube. The heater and anode/screen current warms up the tube. Because of that the so called anode capacity and grid capacity are increasing. Bij warming up the electrodes , like anode and screens, the material of it expands. So the capacity to earth is increasing. This capacity influences the resonance frequency of the various coils. So frequency will decrease.

But especially when there is a high anode and screen current, this effect is increasing. So you have to make the anode and screen current as les as possible. Then warming up gets less. The RV12P2000 has a 12 volt heater, so gets pritty warm, even if there flows no current in the tube. If the heater should be 2 volts, then you get almost no warming up of it.

In my situation:

There are two ways for warming up the oscillator tube:

1 – warming up by the heaters.

2 – warming up when the oscillator is working.

The first cause cannot be avoided.The heaters must have supply. So always a warming up.

The second cause is only happening when key is down during CW Mode.

During receive in CW Mode, the anode gets constantly HT supply, a little anode current is flowing. The sreen gets HT supply during key down at transmitt. but the waming up of the tube is less, so the frequency drift. Increased current will flow at key down (transmitt). During key up (receive), there flows a little current. So is increasing during key down. So warming up and so frequency drift, is during more by key down.

I decreased the drift first by increasing changing the screen resistor of the oscillator, a RV12P2000, , from 12 kohm to 47 kohm. The voltage on the screen went from 123 volts to 100 volts. The screen current from 4,7 mA to 2,5 mA. So the anodecurrent is decreasing at key down.

Second I placed an extra resistor of 15 kohm in series with the ande of the oscillator tube. The voltage decreased from 197 volts to 152 volts. The anode current is now 3,8 mA, less then with the original value of this resister. The oscillator is working still very well, so the start up is. But the drive energie for the PA is some less. The total warmingup has been decreased a lot. So the drift of the frequency.

The drift is very acceptable, because of those changes. Especially increasing the anode resistor did influence the warming up/frequency drift.

You should expect that the power output of the transmitter would be much less. Because the oscillator output is less by the decreased anode current. But the power output of the transmitter is now a little less, about 9 watts instead of 10 watts on CW. But sufficient.

Ofcourse you have to hold on a warming up period of the transmitter, say a half hour to stabilise the the warming up of the oscillator tube by the heater. After that you start to activate the transmitter. And with the precautions of above, you will get the most stable frequency in Hell Mode.

Posted in Army Navy, German Army Navy.

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