SP6a, Stepka mod?

[dubita]

I just picked up an ARC SP6a that was modified by a company called "Sound Engineering" in Rochester NY. Supposedly has the "Stepka" mod.

Anyone familiar with this?

[Myles B. Astor]

Originally Posted by dubita

I just picked up an ARC SP6a that was modified by a company called "Sound Engineering" in Rochester NY. Supposedly has the "Stepka" mod.

Anyone familiar with this?

Be really careful with the "A" version. The output cap that blocks DC failed fairly regularly and could, if you have a DC coupled amp (for instance Krell) produce that hated kaboom! You might want to find if the caps were changed and if not or any question, contact ARC. This problem was fixed in the "B" version

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[dubita]

Originally Posted by Myles B. Astor

Be really careful with the "A" version. The output cap that blocks DC failed fairly regularly and could, if you have a DC coupled amp (for instance Krell) produce that hated kaboom! You might want to find if the caps were changed and if not or any question, contact ARC. This problem was fixed in the "B" version

Sent from my iPad using A.Aficionado

Thanks for the heads up.

arcdb doesn't have a B schematic, but comparing the A to the C and later versions, the only difference I see is the addition of clamping diodes from grid to cathode on the cathode followers, I assume to limit the havoc that would be caused by V2 or V5 failing open. Edit: I just found a reference to start up conditions in the SP-6. If V6 starts conducting before V5, there is excess voltage on the output coupling cap. The same applies to V3 and V2.

This has been updated on my unit.

[tdelahanty]

The power supply was totally redesigned in the 6B and the output stage was coupled with HP opto-isolators instead of caps. The SP6 and 6A had very poor regulation circuits in the power supply. There was a stack of zenar diodes that set a reference for the B+ regulator, they fried themselves on a regular basis. ARC's first attempt at a solid state power-supply was a failure, very poorly engineered.

I had to repair every SP6, 6A, 6B that I owned. These few comments were only the tip of the iceberg concearning p/s problems with this series of pre-amps.

[dubita]

Originally Posted by tdelahanty

The power supply was totally redesigned in the 6B and the output stage was coupled with HP opto-isolators instead of caps. .

Can you point me to a schematic of that?

[JPrest]

I am restoring an SP6-A, I see you did not get an answer here, so I'm posting the question again, as I have the same question, does anyone have the SP6-B power supply schematic?
John Prest