AKG C-24 Connectors, wiring & voltages

[Ivan K.]

Hi All, I'm checking an AKG C-24 that's been in storage. I have the schematic, but not the pin-out of the 12-pin Tuchel microphone connector. The pin numbers are not clear enough to read and I want to check all the voltages before powering up the mic.

I see a primitive pass regulator for the 12.6V filament, but am reading 20+ V unloaded. Does anyone have experience with the N24S supply to let me know what to expect?
Thanks,
Ivan

 

[TLRT]

Heaters are unregulated, calculate the load and add those resistors while testing the psu. It is around 30ohms for 6.3v.(so double for 12.6v) anode dummy load is around 180kohm.

 

[mg73]

Try to get hold of an Variac if it's been in storage for a long time.



"Bring the variac up slowly over a period of several minutes until you reach about 50 volts. This will pre-heat the tube filaments and begin to re-form the electrolytic capacitors. Keep an eye on the current value and be on the lookout for smoke or any malfunctions. The variac should be left running at this voltage level for about 30 minutes.

Next, slowly bring the variac up to around 75 volts. This will allow the power transformer windings in a transformer-equipped set to warm up a bit, driving out any accumulated moisture, and will continue to re-condition the electrolytic capacitors. Leave the variac at this voltage for at least another 30 minutes.

After waiting 30 minutes, raise the voltage to around 90 volts. At this point the radio or amplifier should be functioning. If the unit begins to hum, you will need to replace the electrolytic capacitors. You should probably consider replacing the capacitors on an old piece of equipment even if it doesn’t hum. Old filter caps will fail sooner or later, so you may save yourself some time and trouble later on.

After about 10 to 15 minutes you can raise the variac output to full voltage and verify everything is working correctly. If you notice a sudden increase in current or see or smell smoke, immediately turn everything off."

 

[Ivan K.]

Thanks for the replies! I do have a couple of Variacs and actually took a day to get to full voltage. No problems so far. There is a filament voltage regulator shown in the C-24 schematic, set for 12.6V. The plate supply is just a rectifier and your typical R-C filter.

I need to ID the 12-pin Tuchel. The numbers are not readable. Does anyone have a pinout?

 

[snigglepit]

BTW according to some information I was forwarded by Leo Schaal, there is an error that is common to all versions of the C24 schematic.

"In case you have never encountered this error, it is as follows: pins 10 and 11 are shown to be the remote polarization lines for the ‘fixed’ and ‘moveable’ capsules respectively. AKG actually built it as pins 9 and 11. I first encountered this error in the mid-seventies and it has be confirmed in every C24 I’ve received since."

 

[Gus]

Look closer at what the power supply regulates.

 

[Gus]

I see a primitive pass regulator for the 12.6V filament, but am reading 20+ V unloaded. Does anyone have experience with the N24S supply to let me know what to expect?
Thanks,
Ivan

I would not call it primitive. It is a very nice circuit Think current not voltage.
look at page 8 AKG C 24 Manual
Think V Zener - Vbe divide by R1

 

[Ivan K.]

I would not call it primitive. It is a very nice circuit Think current not voltage.
look at page 8 AKG C 24 Manual
Think V Zener - Vbe divide by R1

Thanks for the reference.