Regulator question

[John Pilgrim]

Hi everyone!
My first post on the Bottlehead forum.

A bit of intro:
I've been wielding a soldering iron and reading schematics for forty years, but more for digital logic and motor control circuitry.
My dad owned a popular electronics surplus store in Berkeley CA in the 1970-90s, and I grew up around hobbyists, students and R&D engineers putting wondrous things together.
I started getting into tube audio maybe five years ago, and spent some time over on two other audio forums in recent years talking about Scott 222C amps and restoration questions.
More recently, I've been putting together a collection of hobbyist-made and one-off single ended triode amps, and studying schematics and tube theory.
Work and kids have so far kept me a bit too busy to build my own, but that time is coming soon enough.

Today's question:
I recently purchased a used Stereomour, and have been reviewing its build against the assembly instructions before powering it up.
The LM431's seem very out of place -- see attached photos.
I wanted to see if anyone recognized any good reason for them to be installed as they are, before I remove them, get fresh LM431's and rebuild the board to match the assembly manual.

Let me know what you think.

Thanks,
John

[John Pilgrim]

One more image

[fullheadofnothing]

That's a Stereomour I.

Thread moved to legacy products.

It's also using PN2907s  vs. 2N2907s. That's a pretty good clue that this amp was worked on by PB and he wired the board in a way that simplified layout (i.e. uses fewer jumpers).

Assuming that the amp is working, there is no good reason to rebuild a board in a working amp.

[John Pilgrim]

Sorry about that.
Thanks for the move.
I edited and corrected the post.

[Doc B.]

My dad owned a popular electronics surplus store in Berkeley CA in the 1970-90s

That one that was down in flatland, maybe on San Pablo or 7th or something? I remember my EE buds getting stuff for their projects down there in the late 70s.

[John Pilgrim]

Yes, it was called "Electronics Etc." and was on 10th Street one block west of San Pablo in West Berkeley.

[Doc B.]

Ah yes, I see the neighborhoods have been much more clearly defined over the years of gentrification and that flatland is now just on the east side of San Pablo. Proof that I went there a looong time ago.

[John Pilgrim]

It's also using PN2907s  vs. 2N2907s. That's a pretty good clue that this amp was worked on by PB and he wired the board in a way that simplified layout (i.e. uses fewer jumpers).

Assuming that the amp is working, there is no good reason to rebuild a board in a working amp.

The amp was represented as working, but I don't have any sacrificial speakers (need to get some), so I'm cautious before powering up new amps.
Reading the datasheet for the LM431 it makes more sense now why pins 1 & 2 are joined together.

Is that the same board as the C4S?
Where is a good place to learn all the different ways the board can be wired?

Thanks,
John

[John Pilgrim]

Ah yes, I see the neighborhoods have been much more clearly defined over the years of gentrification and that flatland is now just on the east side of San Pablo. Proof that I went there a looong time ago.

I don't know anything about the neighborhood boundaries. Berkeley's pretty flat all the way up to at least Telegraph or College. Oakland's flat up to MacArthur.
We've been on Tenth Street since the mid-70s and Fourth Street before that.
I never distinguished much between the east and west of San Pablo Ave.
Whole area's changed a lot.

[Doc B.]

Back in the 70s I think we privileged college kids called pretty much anything below Shattuck flatland. I liked going to Brennans on a Friday afternoon, to get away from the college crowd. The crew from Golden Gate Fields used to come in and take over the bar, and most everyone else there was a practicing alcoholic or a, um, fancy lady. Awesome Turkey sandwiches and cheesecake for cheap.

[fullheadofnothing]

Follow the instructions for resistance and voltage checks. You do not need speakers for those.

[John Pilgrim]

Follow the instructions for resistance and voltage checks. You do not need speakers for those.

Right on!
Thanks

Still curious:
Is that the same board as the C4S?
Where is a good place to learn all the different ways the board can be wired?

[Paul Birkeland]

Yes, that looks like a Stereomour that was likely in for repair, which received a new C4S board.  The manual calls for the TL431 to be installed differently with a bunch of wire jumpers, but the arrangement on your PC board is functionally identical.

I'm not sure how to answer your question about the board itself.  The PC board has two C4S loads and enough extra pads that it was a convenient place to locate the 431s. 

I'm not aware of any complete resource on all of the possibilities for wiring up that board.  There are so many different possibilities for what you can do with the combination of the C4S load and the voltage regulator that it would take some serious time to document! 

[Paul Joppa]

If you look close, you will see that the board is Version 4.4. For a long time I tried to make the same board do many different things, because there are large economies of scale if you buy many boards at the same time. It's a tradeoff, lower price vs. easier to build.

[borism]

John,
I am still using my original Stereomour and here is a photo of the same v4.4 board wired as per manual.