Michell GyroOrbe Pabst AC Motor Power Supply

[User211]

Three days of solid running and the fake belt delivers arguably audible wow & flutter.

I don't think the claim the belt is indistinguishable from the real thing in the eBay listing is valid.

It is obviously different. It looks far more glossy.

Can I tell you why it doesn't perform as well?

No. But it doesn't.

It is generally about 0.1% worse. That is over the line of acceptability IMHO.

Best solution is my probably 10 year old original belt running on the top of the spindle of the two Gyrodec 33 rpm options.

And here is where I found something very repeatable. Of the two 33rpm grooves on the motor spindle, the top one is more accurate.

This shows just how ridiculously sensitive such things are to precision machining.

Think about it. A tiny diameter spindle attachment is driving a relatively huge platter. Any manufacturing error on that spindle is observable by simply running an Android app on a OnePlus 13.

That said, that is state of the art mobile phone tech.

I am quite surprised how sensitive the phone and app are at doing the requested task.

Over loads of tests the trust in it inceases in a way I didn't expect.

[User211]

Source code. Very simple.

TBH there should be enough here to make one quite easily, so I will leave it at this. Just ask an AI if you get stuck.

Anyone has permission to use this even for commercial purposes.

Initialize with a Z?

Are you serious?

Max post regret.

The loop comment is twaddle.

[Alex_UK]

Initialize with a Z?

Are you serious?

Max post regret.

The loop comment is twaddle.

Don’t comment much Justin, but very much enjoy your posts so please keep them up!

[User211]

Glad to hear it Alex.

I'm currently trying to work out why the filament supply to one of the 211s in one of my monos doesn't work.

There's no circuit diagram and it really isn't obvious.

Just got an LCR tester but so far everything measures cool.

The circuit is complex for a valve amp, as you can see.

Might run a thread on it.

If I die it was the 211s

[User211]

Not worth a thread for the 211 issue. It's taken me a while to figure out what I thought was simply a junction box is actually a rectifier.

The rectifier converts 10V AC from the transformer (yellow lead) to 10V unsmoothed DC but the filament terminals connected to this rectifier are also connected to huge 68mF caps which smooth the rectifier output.

For the non-working 211, there is simply no output from the rectifier. Pins 2 and 4 (211 filament terminals) are also connected to a resistor/pot bank for 211 voltage trimming, which I thought somehow must be fed power from some visible rectifier / regulator somewhere. Grok was really into this idea which really threw me for ages.

Then I figured the potting compound is actually hiding something - probably rectifier diodes. Then Grok agreed I was probably right. Testing confirms it.

Thank god the transformer is OK. It's a monster and replacing it would not only cost a load of money but plumbing it in wouldn't be fun. TBH getting it out looks extremely hard. I couldn't even remove the cover for it!

Will order a part and get it sorted soon.

Relieved? You betcha. I love these amps beyond belief.

The faulty rectifier block is bottom left three pics up from this post, with the bolt in the centre of it.

[User211]

Looking at the spec of the part, a KBPC 3502 bridge rectifier (£4.31 eBay free shipping), it is hard to see why it would fail. All it should see is 10V 3.25A but just look at the specification - it is massively overrated.

It should have outlasted most of the stuff in the amp easily I would have thought. Apparently not.

[User211]

Fixt.

The recitifier I was sent wasn't what I ordered but this is a higher spec equivalent. 50A instead of 35A.

Filament voltages are the same on both 211s at 9.8V and it seems to be staying on alright.

[User211]

Next fix: Accuphase M-60 monoblock. Twice repaired already by professionals.

Third time by me, evidentially.

This time no NOS transistors. Plan is both monos get new equivalents plus get properly biased.

This year has been insane. Two amps broken, Michel PS busted, one Apogee bass panel down. All within a few months.

Madness.

But all very fixable

[User211]

This thread should probably have been called "Going public with technical ignorance". In the hope that AI would solve everything.

It didn't. Just regard it as a helpful friend working in conjunction with you to solve your problems.

The trouble with that is Grok is a complete creep. A very well crafted complete creep.

With flaws, like you see in everyone you live with or know.

Curious times.

[User211]

Meanwhile the newly fixed 211 amps are sounding completely insanely good.

Complete rockers on early QOTSA. World class, in fact.