Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: Willabe on March 07, 2023, 01:21:34 pm

Title: Sphere EQ 920 diodes
Post by: Willabe on March 07, 2023, 01:21:34 pm

My friend has a Sphere EQ 920 that is rack mounted and it's not working right.

Can someone please tell me what the diodes are for that are connected to Q3/Q4 Q5/Q6 and Q9/Q10 Q11/Q12?
Biasing?

Thanks Willabe 

Title: Re: Sphere EQ 920 diodes
Post by: sluckey on March 07, 2023, 02:40:17 pm

Not me. My eyes are still burning even as I type this reply!    :cussing:

Title: Re: Sphere EQ 920 diodes
Post by: shooter on March 07, 2023, 02:45:09 pm

I believe;
Q4 n Q10 Base diosdes are "bias" diodes, each will drop .6vdc
the collector diodes do much the same for Q5 n Q11
the one's between Emitter and base I think are "blocking diodes", more thought needed, trees await

Title: Re: Sphere EQ 920 diodes
Post by: Willabe on March 07, 2023, 04:27:54 pm

Quote from: sluckey on March 07, 2023, 02:40:17 pm

Not me. My eyes are still burning even as I type this reply!    :cussing:

Sorry, it's the only schematic he could find. I can hardly read it too.

Title: Re: Sphere EQ 920 diodes
Post by: PRR on March 07, 2023, 10:35:09 pm

Quote from: Willabe on March 07, 2023, 01:21:34 pm

Biasing?

Some of them.

What is "not working right"?

Title: Re: Sphere EQ 920 diodes
Post by: Willabe on March 11, 2023, 11:07:49 am

Quote from: PRR on March 07, 2023, 10:35:09 pm

What is "not working right"?

Thank you PRR. He got it fixed.

It wasn't passing signal when he ran it balanced out to the patch bay, only passed signal unbalanced out to the bay.  :dontknow:

He found a bad diode (he doesn't know which diode exactly, double sided PCB) and installed an output transformer that he didn't know it needed. It had dcv on the output signal. Now it seems to be working fine.

   Willabe