• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Unidentified Grundig mono console questions

"The symptom is: I can't add any bass (tone control) as it distorts."
With the mod'ed output ckt I'm not too surprized. It's possibly somewhat assymetrical with half gone tho' I think the original ckt would need to be operating more in class 'A' P/P than the usual class 'AB' to work right. It's possible the transformer may be near DC saturation without the other tube to counterbalance the OPT. The cap cuts the highs a bit but is spec'ed for the original design and evidently is needed for stability.

Re the Menuette. Have all the function switches been worked /cleaned? Fully recapped and voltages confirmed? Audio tubes checked/swapped for known good tubes? I did re-read the pertinent threads but am obligated to ask the obvious questions, again, as a matter of form. Please forgive the redundancy.
 
Pio1980 said:
"The symptom is: I can't add any bass (tone control) as it distorts."
With the mod'ed output ckt I'm not too surprized. It's possibly somewhat assymetrical with half gone tho' I think the original ckt would need to be operating more in class 'A' P/P than the usual class 'AB' to work right. It's possible the transformer may be near DC saturation without the other tube to counterbalance the OPT. The cap cuts the highs a bit but is spec'ed for the original design and evidently is needed for stability.
Click to expand...

I came to a similar conclusion. The ckt is not what it was supposed to be, hence the bugs... Maybe it'll do a fine guitar amp:guitar:

Pio1980 said:
Re the Menuette. Have all the function switches been worked /cleaned?
Click to expand...

Yes, but maybe not deeply as I should. There's remaining black on the contacts of the switches. Need to do a thoroughful cleaning... I must also clean pots again and test their resistance readings carefully (not done at first).


Pio1980 said:
Fully recapped and voltages confirmed?
Click to expand...

Fully recapped and fully "re-resistorized". About voltages, I remember having done it in phono mode instead of fm and the values were different a lot between the two. I also remember that voltages at the EL84 were not what schematic asked for...

I added a big 750 ohms ceramic resistor after filter caps but I'll have to put it between diodes and first filter cap I think (like the Grundig - Fleetwood where voltages are spot on now). Some work to do on my part here... I'll also have to verify each voltages as indicated on schematic (overlooked this one).

Testing AC on each stage with test tone could help also I guess...


Pio1980 said:
Audio tubes checked/swapped for known good tubes?
Click to expand...

Yes, more than one time when diagnosing...

You made me realize that I forgot several steps in my diagnostic method. Some that I was aware but overlook and some that I didn't think about by lack of sufficient knowledge.

Now, you helped me adding some arsenal to my troubleshooting methods that I'll use in the future when diagnosing recalcitrant tubes gear :D

I have to say a big thanks again to you for opening my mind and my eyes. Is this not what this forum is intended
for? Wonderful!

Obviously, I'll report back also for the Nordmende.

Pics if you didn't see it IMGP1000 to 1020 approximately):
http://s720.photobucket.com/albums/ww209/PatriceBrousseau/latest finds/
 
Oh... and if you don't mind Pio1908, is it possible for you to leave a detailed explanation on the "howto" reconnect tranny in PP. Like this component goes here, this wire here, you should try this... I'll print all this thread as you already gave me some useful hints.

I ask 'cause the set is leaving for the cottage tonight and I do not have any web connection there. As I'll probably attempt to fix it in the future, I'll need some hints on how to do it properly.

Like I said, the priority at the cottage will be to fix the Nordmende first.

Thanks.

Patrice
 
Thank you for your gracious comments. I have not done this sort of diagnostics in some time so getting in some practice treating yours as I would my own has been quite interesting. I will get back with instructions on how I would proceed to re-establish the proper transformer connections.
 
To re-convert to cathode cross-coupled P/P;

The added cathode bypass 100uF/25V Aerovox el'ytic comes out and the cathodes at #3 each socket are again tied together to R503, the other end of which will be shifted to the large orange OPT tie point. The added screen resistor temporarily stays and the screen at #9 of the presently disconnected tube is temporarily tied to that of the working tube with a jumper wire. The cut plate winding for the disconnected tube will now be provisionally installed, connect the blue wire to the same point on the big e'lytic as the other blue and the red to the #7 plate of the disconnected tube. Watch for any fragment of clipped wire that may have insulation on it as we'd want to know color. Install 2 similar performance EL84/ 6BQ5.
Now, plug it in and turn on and see if it sounds reasonably normal and does not whistle, oscillate, or "motorboat" (putt--putt--putt---). If it sounds bad with low volume and/or instability try reversing the red and blue wires we just re-connected. It should work one way but not the other. Once the proper relative polarity is established we next move on to addressing the screen windings.

Remove the added screen resistor and provisional screen jumper.
Connect the cut black OPT wire to the line from the end of R-801 opposite the input rectifier end where the blues went. The yellow and green wires will go to the #9 screen tie points on the output tube sockets. Now, plug it in and turn on and see if it sounds reasonably normal and does not whistle, oscillate, or "motorboat" (putt--putt--putt---). If it does or the volume seems lower, turn off, unplug, reverse the yellow and green wire connections and try again. If it seems to be working normally we may have got it and the transformer and circuit are good and now working properly. If not, we have a reasonable point of departure for further analysis.

If i find any mistakes or missing steps or other goofs I will come back and re-edit.
 
Last edited:
Thanks... I'll print it for future reference when I'll work at the cottage next time...

I'll also give you a report later today about the work I've done on the Nordmende unit this week end.

Patrice
 
You must log in or register to reply here.
Back
Top Bottom