Dampfradioforum

Hello all. My first post. I have an avionics background and studied tube theory in 1976. Repaired old aircraft Narco receivers with tubes, but the basic troubleshooting then was a wet finger to see which tube was cold. Now retired 50 years later in Germany. I can read and speak German but writing is much easier in English.

I now have a Opus 2430 with good FM reception but no Stereo decoding.

I have restored one Telefunken Opus 2650. I have a second 2650 I use for comparison. The decoder board is a bit different, but still useful. There is No audio when Stereo selected. No Stereo Illumination. On the decoder board I thought I found the issue. R906 10K resistor was open. Replaced it and 10 uF C903. It measured around 19 uF. Previously only 5 VDC seen at the junction R906 C903. Now 265 VDC. Also replaced 10 uF C916. Now when On there is nothing heating up in the tube. Remains cold. Completely dark. Heater voltage pins 4 and 5 is 6.7VAC. Cathode pin 7 should have 21 VDC. It is zero. The voltage on pins 1, 3, 6 is high at 265 VDC. Perhaps it will decrease when properly loading the circuit.

The power supply components have been replaced after seeing high voltages. No change. 316 VDC output from rectifier instead of 270. EL95‘s running hot. 100 degrees on V1302 with red plate. 295 volts instead of 265.

Any help would be appreciated. I do not have a signal generator nor an oscilloscope. Voltage readings of many components on the decoder board is impossible as it is hard mounted on top of the main board. I do not have a signal generator or oscilloscope. Yet.

Greg

_________________
Greg Linton
„If it ain‘t broke, don’t fixit.“

Moin,
without a working cathode, the tube does not work and all voltages at the tube can't be correct.
" Heater voltage pins 4 and 5 is 6.7VAC"
That is correct so far, but where measured? If possible, pull the tube a bit and measure directly at the pins.
Resolder the socket. In some cases ist is neccesary to remove the entire socket, clean the solder pins and put it back again.
Did you check the resistance of the filament? May be open ....

(Ohne arbeitende Katode arbeitet die Roehre nicht und alle Spannungen an der Roehre konnen nicht korrekt sein.
" Heater voltage pins 4 and 5 is 6.7VAC"
Das ist soweit richtig, aber wo gemessen? Wenn es moeglich ist, die Roehre etwas herausziehen und direkt an den Stiften messen.
Die Fassung nachloeten. In einigen Faellen kann es noetig sein, die Fassung auszubauen, die Loetstifte zu reinigen und wieder einzubauen.
Hast Du den Widerstand des Heizfadens geprueft? Er kann unterbrochen sein

73
Peter

Wahnsinn! I had measured pins 4 and 5 with tube removed. Pulled up tube to measure and it started glowing and better yet working!

Once again, keep it simple stupid - KISS. I was so deep in the weeds I forgot my golden trouble shooting rules.

Now all other power supply voltages came down and EL95’s cooled down.

Many thanks Peter. Now I can concentrate on the NF portion of my Opus 2650. It worked actually before I fixed it with new caps. Oops. If it ain’t broke, don’t fix it. My second golden rule that I didn’t follow.

Greg

_________________
Greg Linton
„If it ain‘t broke, don’t fixit.“

Moin,
welcome to the club

There is a quite similar radio:
https://www.radiomuseum.org/r/elmug_rossini_g6011.html
or with built-in Speakers:
https://www.radiomuseum.org/r/elmug_rossini_g6010.html

No design ("Hartmansdorfer Hasenstall), "aber es traegt den Pelz innen".
A real high performance receiver, made in GDR.
Seems to be (one of) the last tube radio built in Germany (1967-1969).

73
Peter