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post #1666 of 1669

Hi all,

 

It seems that I have solved my DC events, that triggered the e12 from time to time.

 

I tried to see what happened if using only one channel. So I removed the tube of one channel at a time. I tried all permutations of channel tube removed and tube. As a conclusion: one channel at a time was always working. But two channels at the same time generated those DC events. It could comme from a load problem on the power supplies.

 

So I went again through the initial setup sequence to check the voltages and idle currents. Not changed a lot, but had to adjust slightly the tail current of the input staage of one channel.

 

And now seems to work wothout DC events. Let's see over what happens the weeks...

 

Regards,

 

JM

post #1667 of 1669

I am working on building my SOHA II and I have the BOM at mouser. Problem is two of the transistors are no longer avaiable, the fairchild MPSA42RA and the Fairchild MPSA14_D74Z.  Any ideas on replacements for these, the MPSA14_D74Z is Q1p and q2p in the power supply and the MPSA42RA is q3e on the epsilon 12. thanks

post #1668 of 1669
Quote:
Originally Posted by scottie4442 View Post
 

I am working on building my SOHA II and I have the BOM at mouser. Problem is two of the transistors are no longer avaiable, the fairchild MPSA42RA and the Fairchild MPSA14_D74Z.  Any ideas on replacements for these, the MPSA14_D74Z is Q1p and q2p in the power supply and the MPSA42RA is q3e on the epsilon 12. thanks

 

I think you've swapped the descriptions, the MPSA14 is part of the e12 and the MPSA42 are in the power supply

 

Try these

 

512-MPSA42_J18Z, you may need to bend the leads slightly, also EOL but they're still in stock now

 

863-MPSA14G, works perfectly in a build I recently did that cloned the simplified e12 in the SOHA II

post #1669 of 1669

thanks, I will add them to the BOM at mouser.  I am also going to try 610-MPSA14 and 512-MPSA42, this is what mouser says are substitues for the original.  I will try both of the replacements for each of these transistors and post on here what I findout

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