Soviet East German Radio

[Nowhere-Man]

In older books the reference is the meter. So, F J Camm quoted the customary 300,000000 metres per second as reference to speed of light. Camm then used a 200 metre wave to give a frequency. In his day I imagine a 13 metre wave was far from typical. The light vs earth year sums I found tended to use miles but they take the maximum and minimum distance from sun to earth (in Jan and July, I think to apply an average orbit to a light year. Obviously you need pi as well. I worked out that 57 minutes in space at the speed of light should equate to one earth year. They did use an atomic clock to read Yuri Gagarin's flight speed around the globe. If light speed had been possible his 50 odd minutes on board should be a year on earth. Also of interest it only takes light about one hour to reach Europa.

[Nowhere-Man]

I recommend Contact the Jodie Foster movie that deals with radio, HAM and SETI. Maybe they based her role on Tesla who was very keen on pumping out high voltage radio waves into space. Also interesting is the strange phenomena on the very high frequency bands during the Aurora Borealis. Most people have seen Contact but, if not, it's a great film.

[Nowhere-Man]

This project hasn't bbeen forgotten. I got myself into very detailed circuit analysis because I think I may be able to accurately diagnose the problem with more circuit familiarity. The UKW has a variometer and tuning mechanism and I had to carefully trace the voltages. The IF at UKW is clearly reaching the ECH81 but probably bypasses R12 where voltage ought to kick in on Medium waves. As access to the Band contacts is poor, all I could do for now was use Servisol which has helped. For now all the effort is in circuit analysis. Most Grundig sets have screws for removal of the waveband mechanism and easier access.

[Nowhere-Man]

My brains have been sozzled. Could be all the different designs are leading to the odd cerebral meltdown. For example many vintage American mixer stages show the triode oscillator distinctly, with the LO signal injected into the cathode of a pentode. Now, my German Saalburg seems to have 2 screen voltages. In one HT feed is a 5000 picofarad capacitor, clearly for RF. I had to check this for clarity and found 1000 picofarads also used for screens. The schematic gives 2 voltages for the eECH81 screen so that is useful to know. I can figure out the switch contacts via what voltages I read on ECH81. However, I did suffer a huge wave of mental blocks tonight caused by viewing differences in schematics. Hopefully I got this right but will sleep on it. The IF cans are for UKW and lower 455 IF's.

[pwdrive]

Another method of oscillator injection to a pentode mixer was via the pentode's screen grid as in the legendary HRO receiver, one of the best comms receivers that was made in the 1930's:

https://images.campyent.com/sites/defaul...pg17-1.png

Lawrence.

[Nowhere-Man]

A simple thing I noticed tonight about the Saalburg schematic is the EZ80 is heated on the same winding as the other valves. This is apparently typical of the EZ80. Interesting that the EBF89 which is a double diode pentode, has a diode passed to ground and the grid used in IF amplification.
Based on the diagram so far I have a feeling the first knob is where I'm losing the voltage but ECC85 is not effected.
EABC80 so far is a bit over my head - triple diode triode.
You may wonder why ponder the schematic so much. The answer is I'd like to better understand the circuit before going in a bit deeper. Whereas at first I was clueless it now gradually makes a bit more sense.

[ppppenguin]

Ask yourself WHY the EZ80 can be heated by the same winding as the other valves.. It's worth understanding this.

[pwdrive]

A simple thing I noticed tonight about the Saalburg schematic is the EZ80 is heated on the same winding as the other valves. This is apparently typical of the EZ80. Interesting that the EBF89 which is a double diode pentode, has a diode passed to ground and the grid used in IF amplification.
Based on the diagram so far I have a feeling the first knob is where I'm losing the voltage but ECC85 is not effected.
EABC80 so far is a bit over my head - triple diode triode.
You may wonder why ponder the schematic so much. The answer is I'd like to better understand the circuit before going in a bit deeper. Whereas at first I was clueless it now gradually makes a bit more sense.

The EBF89's diodes were sometimes configured as a detector diode and separate AGC diode, but as you've observed that's not the case in this receiver because just one diode provides both AM detection and the AGC voltage, that now makes the 3rd diode in the EABC80 redundant, originally the diodes in the EABC80 were designed to provide FM detection using two of its diodes and AM detection/AGC using the 3rd diode, the EABC80 might look a bit complicated but it's not, two of the diodes share a common cathode with the triode, the other diode has a separate cathode, one of the common cathode diodes along with the separate cathode diode is used for the FM detection, the other common cathode diode would have been used for AM detection/AGC but not in this receiver because that function is being performed by one of the diodes in the EBF89.

Hope this helps.

Lawrence.

[Nowhere-Man]

The EZ80 will have a higher heater voltage and normally the heater voltage will be less. Last night I was still on the signal and oscillator stages. These days I do more schematic work than actual applied work because I feel there are gaps in my overall understanding. For example notice the IF and mixer stages in American HAM sets. As I said before cathode signal injection is often found. The HAM schematics I find easier. I will comment on the detector stages later.

[ppppenguin]

The EZ80 will have a higher heater voltage and normally the heater voltage will be less.

Please explain a little more carefully. The EZ80's heater voltage is meant to be 6.3V however you use it.