Soviet East German Radio

[Nowhere-Man]

"L23 is tertiary winding, it fits the bill as described in the books because it's tightly coupled to the transformers primary as indicated by the common tuning slug coupling it to the primary winding (L25) you can also see that the audio output on FM is taken from that via a simple filter network and ends up at switch contact 17."

Agreed. I located C51 and 17 switch contact. It's much better now I swatted up a bit, although I still need to keep redoing the schematic to consolidate it. Not sure about the AVG yet. The more I trace it through the clearer it gets bit by bit.

[pwdrive]

"L23 is tertiary winding, it fits the bill as described in the books because it's tightly coupled to the transformers primary as indicated by the common tuning slug coupling it to the primary winding (L25) you can also see that the audio output on FM is taken from that via a simple filter network and ends up at switch contact 17."

Agreed. I located C51 and 17 switch contact. It's much better now I swatted up a bit, although I still need to keep redoing the schematic to consolidate it. Not sure about the AVG yet. The more I trace it through the clearer it gets bit by bit.

The AGC rail is reasonably easy to trace, as said earlier the AM detector diode in the EBF89 supplies the AGC voltage and also the voltage for the grid of the tuning indicator, the voltage for the grid of the tuning indicator is supplied via R41, the AGC line voltage is supplied via R21, if you follow the AGC line through you'll see that it is, in effect, connected to the control grid's of the Mixer and the IF amplifier valves, more -ve means less gain.

Lawrence.

[Nowhere-Man]

Looks like R18 will be the AVG bias resistor at 1 Megohm. I feel now I have a basic grasp of the circuit and am ready to "shock the world" with dynamic, shock and awe repair work. (Joking)
It is clear by now the 10.7 Megahertz IF is being amplified by ECH81. It is passing through the FM IF cans and being converted through the ratio detector circuit to audio. R12 is being bypassed so has no voltage for AM so the ECH81 Triode oscillator is idle. So no 455 KHz IF.
Best and safest bets: Mechanical fault in pushbutton mech, actual break in circuit in between the sandwiched waveband board (tab soldered to the PCB). Or sheer dirt. My plan is to see if I can get a lense under there.
Other sensible options as suggested is to use the tracks for clues. I have already carefully checked for broken wires but no harm in further checks.
Also the capacitors.
When doing voltage tests on my boat I have to be very careful. I have no test bench nor clamps. I use one arm and try to be aware. For certain that output transformer can kick like a mule.

[Nowhere-Man]

"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,"

I thought I would throw that back up as I've been examining this 10.7 Meg and 455 KC circuit (in prepaaration for intervention). I am so busy doing my boat restoration that all my radio work is now limited to theory late at night.
Strangely I forgot my modulation index work so had to revise it from zero. I also had to learn logarithims due to decibels creeping in.
Anyway, this EABC80 circuit had me busy. Look how the cathode is in circuit with L24 (ratio circuit) I spent a good deal of time checking out grid resistances and bias as well as the variometer circuit.
By day, laying out wall tiles is aa bit more down-to-earth.

[Crackle]

Wall tiles! in a boat?

Mike

[boater sam]

Yes,Mike. We are very civilised on boats, we have tiled showers, kitchen splash-backs etc.
Along with solar power, central heating, washing machines, electricity! Gas! Radio! TV! Wifi! Hot and cold running water! Oh, and flush toilets.

Have you ever been on a decent narrowboat?

[Crackle]

No I have to admit to never going on a narrow boat, all my boating has been done in sailing yachts in the open sea. You would not normally consider adding excessive weight such as ceramic tiles on a yacht. It could effect stability and hence seaworthiness. If you get a knock down in heavy seas, you need the boat to pop upright again and not turn turtle.

Mike

[Nowhere-Man]

I will update this in my boat topic to save going off thread. I found I had problems getting the tiles to stick on the old tongue and groove. Most amateurs use No Nails but I found the quality of this glue pretty poor. I now have laminate glue which is better. White tiles can be dirt cheap and look OK. I got very irritated by other boat people scoffing at my efforts to restore this fibreglass boat and am now determined to show that fibreglass still is a great inland boat. Indeed in the 70's such boats were a majority on the canals and there is enormous pleasure in giving such a boat a new life. Later I will post some pics and one bonus is the GRP won't block transistor radio reception. Tiles were just 13 pence each at Tile Giant and I have a cheap tile cutter (wheel and jaws).

[pwdrive]

Tile backer is the stuff for a backing for wall tiles, eg: Aquapanel etc.

Lawrence.

[Nowhere-Man]

Tiles almost done and the boat looking good. Late at night I still work through the Saalburg schematic. I am doing no applied work as my boat is priority at the moment. However, tonight I studied the Saalburg oscillator layout. Has anyone noticed the grid resistance for most triode oscillators is typically 47 K? Not the Saalburg though. However the winding switches seem pretty standard. As we already know ad nauseum, there is an FM LO apart from the triode one but studying the switches is helpful.
At some near point I'll understand very well how this radio works. It's maybe strange to put so much work into a foreign set for no economic benefit but I feel I learned a fair bit.