Spec 1 and 2 restoration

I always tell the guys what's the big hurry? I don't know why I feel I need to move through this set. A little apprehension - I think, is the amp setup procedures. It looks interesting. The anxiety over completing the amplifiers and untried setup procedures is driving it. Once past it, I can relax and enjoy the work.

Guess what I'm getting ready for? :yes:
"A Little Scared"

No balls, no blue caps.

Remember to breathe.

I ran into a few problems:
Dim bulb start up went well. Each amp assembly at a time.
No idle current, stayed in protection.
Found out I had the RL5 relay installed incorrectly on both boards, configured them properly.
Powered up and set stayed in protection. No idle current or output base voltage.
Found D40 in backwards (Heatsink overtemp circuit), tested and installed correctly. Still stays in protection.
Double checked everything and spent several hours checking voltage.
Removed Q11 (2SA733) and disabled the protection.
DC balance on one amp was -85mV's and the other was -45mv's. Original Q1's, (2SA798's) are installed in the boards.
Idle current can be adjusted to specs.
Thinking about this "EW" mod.

DC offset tweaking on a breadboard

How much "Offset" can this Spec 2 withstand?

I am still formulating a plan.
I ordered a set of the 2SA798's and I'm thinking of flipping the Q1's 180 degrees and seeing what that shows.

Quit for the day :drool:

No guts, no glory. It's all in the boards.. Patience grasshopper.

You were just waiting to say that to me!

I flipped the 2SA798 a 180 degrees on one amp and the DC Balance went from -85mV to +85mV's. So I matched up a pair of KSA992's and got the Balance down to 6.5mV's Did the same to the other amp and now both assemblies are adjusted and almost identical in settings. :yes:

Still having issues with the protection.
I must of done something. :scratch2:

Why six wires on your replacement bias relay?
Two for the coil voltage, two for the bias 'signal', and two for...?

Its an illusion. I curly-cued the red leads for easier install. They are just as you devised years ago and the amps are good.

This protection is fighting back. The only thing it's giving back is a lesson in the operation.
I eliminated the DC Balance by lifting the input resistors (R3 and R4) from the amps. I disconnected the heatsink temp circuit and still its stays in protection. If I remove Q11 it comes out and stays out of protection. Currently I'm looking at the circuit towards Q13.

I found it!
My fault! ArFFF! :nono:
I saw I had too high of voltage at the emitter of Q11 (10.5v, needed 7.7v). So I traced it back to the strange regulator that supplies the 7.7v's to the emitter of Q11 and found a resistor I had desoldered and failed to solder back. I think it provides the differential voltage for the transistor to switch over.

I looked a million times (Right on the edge of the board).

Not a complete waste of time as I gained a good lesson on the protection circuit. Reading the description and operation was invaluable.

Nice find,maybe you're gettin old too!

zebulon1 said:

I found it!
My fault! ArFFF! :nono:
I saw I had too high of voltage at the emitter of Q11 (10.5v, needed 7.7v). So I traced it back to the strange regulator that supplies the 7.7v's to the emitter of Q11 and found a resistor I had desoldered and failed to solder back. I think it provides the differential voltage for the transistor to switch over.

I looked a million times (Right on the edge of the board).

Not a complete waste of time as I gained a good lesson on the protection circuit. Reading the description and operation was invaluable.

Click to expand...

Ah young grasshopper you have solved another of life's mysteries. Soon you will have to leave this place and wander in the desert sands of Las Vegas!

Will you stop it!!