Can you run Full Wave AND Full Wave Bridge AND Dual +/- off one C.T. Winding?

[jeff]

Working on a Marshall TSL 100(notorious for its bias drift) and see this:
Looks like a full wave bridge with caps for bias
                  full wave for +V
And            Dual +/- power supply for chips
All off the same C.T. transformer winding. Is this kosher? Could this be the reason these amps are infamous for bias drift?
Would changing current draw from the other rectified voltages mess with the bias voltage?
Would heat affect the caps causing the bias drift?
Would it be better if the bias had it's own, separate, dedicated winding?
Am I barking up the wrong tree?
Thanks
First schem actual schem
Underneath, it's broken down to its 3 parts for ease of reading

[PRR]

Thanks for the re-draw. But show us the original.

Is it this?
https://www.thetubestore.com/lib/thetubestore/schematics/Marshall/Marshall-JCM2000-TSL100-100W-Schematic.pdf

Then it is not the same. The HV and bias come from different windings.

> All off the same C.T. transformer winding. Is this kosher? Could this be the reason these amps are infamous for bias drift?
> Would changing current draw from the other rectified voltages mess with the bias voltage?
> Would heat affect the caps causing the bias drift?
> Would it be better if the bias had it's own, separate, dedicated winding?
> Am I barking up the wrong tree?

1838 – "Instead of having treed their game, gentlemen will find themselves still barking up the wrong tree." – Mr. Duncan of Ohio in the United States House of Representatives

[HotBluePlates]

... causing the bias drift?

On another forum, a professional tech whom I know to be sharp advises to skip everything else and replace the board.

Unfortunately, the design/layout of the original board leads to conductivity between parts that should be separate, and can only be cured by replacing with a different design/layout.

[jeff]

... causing the bias drift?

On another forum, a professional tech whom I know to be sharp advises to skip everything else and replace the board.

Unfortunately, the design/layout of the original board leads to conductivity between parts that should be separate, and can only be cured by replacing with a different design/layout.

Called Marshall, 'unfortunatly' they can't/won't sell me a new board. The 'only way' to get one is to buy one populated.
$200 of parts I don't need to get the 50¢ 'non-selfdestructing' board.
Gross.

[jeff]

Thanks for the re-draw. But show us the original.

Is it this?
https://www.thetubestore.com/lib/thetubestore/schematics/Marshall/Marshall-JCM2000-TSL100-100W-Schematic.pdf

Then it is not the same. The HV and bias come from different windings.

> All off the same C.T. transformer winding. Is this kosher? Could this be the reason these amps are infamous for bias drift?
> Would changing current draw from the other rectified voltages mess with the bias voltage?
> Would heat affect the caps causing the bias drift?
> Would it be better if the bias had it's own, separate, dedicated winding?
> Am I barking up the wrong tree?

1838 – "Instead of having treed their game, gentlemen will find themselves still barking up the wrong tree." – Mr. Duncan of Ohio in the United States House of Representatives

Connector 14 of the first page(TL-10-60-02.DMG) connects to connector 2 of the 3rd page(TL-10-62-02.DMG)
They aren't numbered in a way that makes it easy. The 14th connector of the motherboard is connected to the 2nd connector of another board.
To be clear, I mean the bias, +/- for chips and switching are all connected to the same winding, seperate from B+, but shared for bias, +/-, switching.

[jeff]

W11
W12
W13
Is the shared CT winding

[jeff]

Here’s the schematic with jumper and xfmr readings.
Even if this is not the cause of drift could you please explain what’s going on with the bias rect?
Thanks

[sluckey]

D7, D8, D9, and D10 make up a full wave bridge rectifier for the bias supply.

[jeff]

So, it's a full wave bridge andthe C.T. is grounded?

[pdf64]

Merlin suggests to think of that arrangement as a dual rail supply using a pair of 2 phase rectifiers.
See http://www.valvewizard.co.uk/bridge.html

It’s ubiquitous in solid state stuff, eg https://el34world.com/charts/Schematics/files/Marshall/Marshall_lead12_12w_3005_5005.pdf

[jeff]

Thanks for helping me understand.
BUT...
I don't think that's the same configuration. D7 and D8 are grounded AND the transformers C.T. is ALSO grounded.
How can you ground both?

[sluckey]

D7 and D8 are grounded AND the transformers C.T. is ALSO grounded.
How can you ground both?

C43 and C44 must make this possible. A 22µF cap looks like a 120Ω resistor to 60Hz line frequency. If you take those caps out of the circuit, D7 and D8 will quickly burn up, maybe even take out the transformer.

[jeff]

OK, so can heat(tubes half burried in chassis) affect those caps thus messing with the bias voltage?
Or
Could the switching/+/- current draw changing(by switching channels) affect the bias voltage?

[jeff]

My gut's telling me, remove the caps, lift the C.T. ground, for full wave bridge bias supply, and install a separate xfmr for the other stuff(switching/+/-chip voltages)
In other words a dedicated bias tap and a separate xfmr for the other stuff
Crazy?

[pdf64]

My gut's telling me, remove the caps, lift the C.T. ground, for full wave bridge bias supply, and install a separate xfmr for the other stuff(switching/+/-chip voltages)
In other words a dedicated bias tap and a separate xfmr for the other stuff
Crazy?

Yes, crazy.
And the bias will probably still drift unless the board is replaced.

[HotBluePlates]

OK, so can heat(tubes half burried in chassis) affect those caps thus messing with the bias voltage?

You're not following the intent of what I posted before:

On another forum, a professional tech whom I know to be sharp advises to skip everything else and replace the board.

Unfortunately, the design/layout of the original board leads to conductivity between parts that should be separate, and can only be cured by replacing with a different design/layout.

You're hoping something with the circuit-design is what is causing the problem.  But I'm pointing you over to a forum full of very sharp professional techs who have battled with this one amp and found the PCB layout is to blame.  I promise you, they don't like having to buy a $200 part either.  But the problem cannot be fixed without replacing the board to get a better-functioning layout.

[jeff]

I understand.
I have utmost respect for you. I used to post a lot on this forum, and you have helped me and taught me more than you'll ever know throughout the years. Much respect.
1)I'm 100% in agreement the old board should/will not be used.
2)I'll be damned if I'm giving Marshall $250 for $245 worth of parts I DON'T need in order to get the 50¢ circuit board to replace the faulty one that came with the amp.
So I'll be rebuilding it myself.
The thing is: Is it a good idea to run all three of these rects. for the different voltages off the same winding?
I have no idea what that rect for the bias is, it looks like full wave bridge...but the c.t. And diodes are grounded.
What is the name of that circuit?
Does it play well with the others?
Are the caps temp sensitive?
That rect is foreign to me, and if I am going to rebuild the thing from scratch(not reuse bad board) would it be worth while to run the bias alone off the main xfmr and get an accessory xfmr for the other supplies.


I dunno know if I'm explaining myself, but 100% agree, get rid of old board, Also, if I'm rebuilding it anyway should I use the same circuit.
Yes, board is cause of drift
but also, should I use this circuit or a dedicated bias winding?

[jeff]

Can anyone please tell me the name of this bias rect circuit?
I would like to learn/understand how this works.
I understand how full wave bridge, full wave, half wave, dual supply, multiplier, rects work but have never seen this particular rect before.
Please, forget I mentioned Marshall, I just want to understand how this circuit works so I can learn more about circuits but I don't know what to search.
Thank you.

[sluckey]

Search for voltage doubler. Your circuit is at the bottom of this page...

     http://www.augustica.com/full-wave-voltage-doubler-tripler-and-quadrupler-ezp-36

Ignore D1-D4. Your bipolar +15V is D5-D8. Your bias circuit would be D9-D12.

If you search long enough you'll probably find an actual name for the circuit.

[jeff]

Is this right for pos neg swing?

[jeff]

Thanks sluckey, just saw your post

[sluckey]

Is this right for pos neg swing?

No. You don't need the caps because none of the bridge diodes are connected to ground.

[thetragichero]

1)I'm 100% in agreement the old board should/will not be used.
2)I'll be damned if I'm giving Marshall $250 for $245 worth of parts I DON'T need in order to get the 50¢ circuit board to replace the faulty one that came with the amp.
So I'll be rebuilding it myself.

so i am all for saving some bucks but my time is also at least semi-valuable. how many hours will you invest laying out/fabbing/populating your own board? my guess is that all of those hours * whatever the minimum wage is in your area will add up to more than the $250 marshall wants

if you're gonna spend time laying out a pcb why not choose something that could help the diy community, dumble or trainwreck or something?

[jeff]

Is this right for pos neg swing?

No. You don't need the caps because none of the bridge diodes are connected to ground.

Now I'm really confused. W12 is the C.T. And is connected to D7 and D8.
Am I reading schematic wrong?
Is my drawing above schematically the same to Marshalls?
I must be missing something

[pdf64]

Is this right for pos neg swing?

No. You don't need the caps because none of the bridge diodes are connected to ground.

Now I'm really confused. W12 is the C.T. And is connected to D7 and D8.
Am I reading schematic wrong?
Is my drawing above schematically the same to Marshalls?
I must be missing something

You are connecting the negative output of the FWB to circuit common. How’s that going to get you a negative output from the rectifier? Sorry if I’ve got the wrong end of the stick.

[sluckey]

Is this right for pos neg swing?

When you said that I assumed you were talking about the +15VDC bipolar supply, not the bias supply.

I think we've beat this horse to death! No need to keep beating a dead horse. If you ain't got it by now you probably never will. Let it be.

[jeff]

Is this right for pos neg swing?

When you said that I assumed you were talking about the +15VDC bipolar supply, not the bias supply.

I think we've beat this horse to death! No need to keep beating a dead horse. If you ain't got it by now you probably never will. Let it be.

OK I'll drop it, but you see how I could get confused if my question was about the bias circuit and your response was about the +/-15VDC.
I don't think it's a matter of me never getting it but a matter of me explaining my questions better and more clearly.
Maybe I never will get it, or maybe we're just not beating the same horse.
Peace.
I have great respect for you, it seems the more I try to explain myself the deeper I dig myself in a hole

[PRR]

Am I reading schematic wrong?
Is my drawing above schematically the same to Marshalls?

No Opinion. Marshall's drawing is REALLY unclear. Connections implied not drawn-out or labeled fully.

Do what you have to do. For smoke-test, use the lamp limiter, both without tubes and with tubes.

[jeff]

Schematics ARE spaghetti.


I don't know how this post got so far off the rails. My original intent was: If you run 3 types of supply voltages of the same C.T. winding, if one system fails, draws too much current, could it throw the others, most importantly the bias voltage out of wack. Is it a good idea to share.


My intent was never to make the old board work, in fact I stripped it before even writing the original post. I'm PtoP rebuilding all high voltage circuits, just wasn't sure if sharing a winding would comprise bias voltage in the event of a chip/switching failure.


Peace