• 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

Help with repairing a SAE 2600

I'm confused. If the fuses are removed and supply voltage is low, then it would be in the power supply. But, you also said it oscillates and transistors get hot. Did you mean it stays at 80v whether the amp fuses are in or out? Which again means the power supply needs to be looked at, and possibly the amp circuit too.
 
Isn’t the only item before the fuses the bridge rectifiers aside from the transformer. I wonder if the 80 volt was measured before the bridge rectifiers. If it was I don’t see how there are but a couple choices for what’s wrong.

The other curious point is that it operates fine driving one side at a time and either side at that.
 
Racingh11 said:
I'm confused. If the fuses are removed and supply voltage is low, then it would be in the power supply. But, you also said it oscillates and transistors get hot. Did you mean it stays at 80v whether the amp fuses are in or out? Which again means the power supply needs to be looked at, and possibly the amp circuit too.
Click to expand...
I clarify:
With the fuses disconnected I measure + -80V at the ends of the 10000uf electrolytic capacitors, for both channels.
If I reconnect the fuses I always measure + -80V even applying the input signal but, as soon as I increase the input sensitivity to -3 or 0dB, it starts to self-oscillate, the voltage drops to + -69V and the power transistors overheat.

The strange thing is that if I apply the signal to only one of the two channels, that channel works fine !!!

I believe that + - 80V are too few, in fact measuring at the ends of the 51 V - 2% CR11 zener diode I find only 42 V !!! The diode is good measured with the tester.
Now I'm going to try running the 240V amp through a Variac.
 
If this was mine and the Variac test fails I’d tear it apart and pull the transformer out. Apply voltage into it and measure the output. If still wrong then it would be the transformer, either bad or wrong replacement got put in. If it read correct then I’d be first going over all the main wiring to make sure correct, etc. Then move forward.
 
Last edited:
+/- 80VDC is suspiciously close to the 2400 voltages. Any part numbers on your xfmr? Did you ever measure the voltage across the 51V Zener? Try monitoring that voltage as you change the gain settings.
 
llwhtt said:
+/- 80VDC is suspiciously close to the 2400 voltages. Any part numbers on your xfmr? Did you ever measure the voltage across the 51V Zener? Try monitoring that voltage as you change the gain settings.
Click to expand...

On the transformer there is this number:
15-0120
Do you have any info on this p/n?

At the heads of the 51 V zener I measure approx. 41 V
 
Last edited:
No info on the xfmr yet. Looks like the front end voltage regulation is not working because the voltages are too low. The 2400 uses 3.9K 1W resistors whereas the 2600 uses 6.8K 2W because the voltages are so much higher. As an experiment try replacing R12/13 with 3.9K 1W resistors. This will raise the voltages to where the Zener can operate normally and possibly solve your oscillation problem.

Craig
 
What you suggest me to put the drop resistors towards the zener of the 2400 model may be fine to eliminate the self-oscillation but it certainly will not solve the problem of maximum power !!!!
Now I have to find the transformer of the model 2600 set to 240 V, can you help me? Do you know anyone who could sell it to me?
Thanks
 
The only place I think you'll find one is someone parting out a 2600, don't hold your breath. Now you have a SUPER 2400 along the lines of the Dynaco ST-416, double the output xsistors of an ST-400. Another problem is that some 2600s had Ei xfmrs so that again limits the availability.
 
llwhtt said:
The only place I think you'll find one is someone parting out a 2600, don't hold your breath. Now you have a SUPER 2400 along the lines of the Dynaco ST-416, double the output xsistors of an ST-400. Another problem is that some 2600s had Ei xfmrs so that again limits the availability.
Click to expand...
Thanks Craig for the valuable suggestions
 
You must log in or register to reply here.
Back
Top Bottom