WF PG1 Prüfgenerator

East german product. With tube technology. From 50ies. Obsolete, Outdated. Unhip?

The root of all this came from Corona agony. I thought: Why not to look again to tube technology?

Device after cleanup and fixing

Last year a friend gave me an old tube radio as a gift. I love the sound of this small Lowe Opta Bella Luxus and handled it like a religious device, e.g. the Bundeslade.

Time passed and I thought: why not getting another tube radio.
I bought a non working Lowe Opta Meteor 53 from 1953. 15€. An old lady had this thing for ~40 years, all time in defect state.

Looking inside, it was all dust and dirt. It uses an ordinary, poor EF80 in UKW tuner. Wow.

After checking optical tubes (all are glowing) I understood that I really need more support that thing, To do real radio testing, its obvious 🙂 to have these tools in lab:

HF generator, able capable to create AM/FM modulated signal.

An Signal tracer, if possible for HF and NF signals.

Some days later I got the WF PG1 Prüfgenerator from an ebay auction. It is east german technology from early 50ies. 5-235Mhz, AM and FM modulation.

WF means „VEB Werk für Fernmeldewesen“ in Berlin. Gerät must be from around 1952.

Despite many west german people consider east german technology as being poor, aged and poverty-driven, this device may even service as how to do it in the best way. After opening the device and checking it, it is obvious that the engineers were trying to do the best possible with devices and technology from the 50ies, at no cost. Everything inside the PG1 is build like being part of a Panzer. I mean a rugged military device. Build to last as long as possible, maybe forever,

I found the device to be operating inside its original specs after 70 years. I could only test it up to 160 Mhz, because my Rigol 1054 only triggers up to this frequency. But I assume it will work up until original guaranteed 250 Mhz.

After opening case for first time

Only thing that did not work was FM-Modulation. Modulation is done by some EF80. Because I have bought a 140 tube convolut :), I was able to replace the old tube with a new (NOS) EF80. And: FM-modulation was back.

(*NOS=New Old Stock, tubes build dozens of years in the past, so „old“, but never used before, so „new“)

Scheme from manual

A short look at the interesting (at least for me 🙂 ) scheme:

In the upper left, the oscillator can be seen, based on an ECC81 double triode. 12 different frequency ranges can be selected with rotary switch S1. This switch changes the value of a resistor. Inside a selected range, frequency adjustment is done with variable cap C5. There we can read „5 .. 235 Mhz“.
For FM modulation, the input signal comes via W6 (resistor 6) and germanium diodes Gr1-I/Gr1-II.

The oscillators output signal then is an input to the modulator section (upper right). Here we have an ECF82 Pentode/Triode. AM-Modulation comes in via coils Dr1/Dr7 (Dr means „Drossel“, which means coil). I assume the oscillator signal is not only AM-modulated, but also improved/amplified by modulator section.
Because output signal strength varies by frequency range, we have an „Eichen“ (calibrate) pot named RW1. The output signal strength is displayed with instrument J1 and can be calibrated with RW1.

The generator can have an external signal („Fremd-Modulation“) or an internal 1 KHz signal generated by the section in the lower right with the EF80. This is both for AM and FM modulation.

Final section is lower left, power supply, called „Netzgerät NG1“. This is all semiconductor-less. Wow. For all tubes, the heater AC is provided by line transformer in different coils to prevent any interference – nice detail. Plate DC voltage comes from a EZ80 rectifier. The DC is cleaned from ripple with coil Dr1, caps C2 and C3. Tube STR 150/30 regulates the plate voltage to 150 volts (and I suppose 30 mA). I never was aware before that there were voltage regulating tubes.

Power on gas lamp was not working. I replaced this with a nowadays red LED.

Cleaning up the whole device was next. After this it looks quite beautiful again.

After some cleanup
Modulator block at the left, power supply in the middle and at the right

Based on this device, I found that the HF-amplifiying EF41 in my Meteor 54 radio did not work anymore.

I ordered that tube (as NOS) for ~6 € from reichelt.de, replaced it and the radio gives a good sound again -after at least 40 years or so of being defect!

Modulation switch (externally modulated FM, AM(Ton), AM(Video) and 1Khz modulated FM and AM. The instrument is used together with the „Eichen“ knob to somehow calibrate the device
This chain has the size of a bike chain and is used to transfer rotation from hand crank-wheel to the big variable cap used frequency adjustment

NEVA Netzgleichrichter for experimenting with Tubes

To experiment with tubes, a power supply that creates higher voltages is required. Most lab power supplies supply up to 30, maybe 50 volts, some older ones may even go up to 100 volts.

While tubes operate already somehow at these values, for testing etc., I looked for a real tube power suppy.

I found one from an older german company, called NEVA. As far as I can see, they mostly produced for universities and school labs. The power supply is older and looks like being produced in late 70ies or early 80ies.

It offers 6.3 volts with 3 ampere for heating . An adjustable plate supply voltage from 0..+250 volts at 15mA and an adjustable gate voltage 0..-50 volts at 15mA. It also offers an unregulated plate voltage of 300 volts, then at 100mA.

This was for 220 volts regulary input supply, today we have 230 volts, so the real output is higher. The fixed plate output is about 380 volts and the adjustable output maximum is about 370 volts (with a single tube as load).

Build quality is high. The technology of power supply is simple. Just rectifier, caps and resistors.