Music Man Power Supply [was Re: #102 died yesterday :( how,why]

[Bombacaototal]

Tony and Rootz, I was calculating the voltage divider for VC- (tremolo negative voltage for startup). With 1M and 270K (as per my schematic), with a voltage source of -150V (C-) I am getting -31.9V. I belive Fender uses -50V. If its placed right after the voltage doubler, with the voltage source of -197.4, the output voltage will be -42V (more in line with Fender). I am then assuming that the VC- network will be right after the voltage doubler and before the dropping resistor. Is my rationale correct?

I hope more folks can chime in on the bias network as well and on where might the PI Driver be, along with where would the second 40K be placed.

[Bombacaototal]

Question about EF86. What is the use of PIN 2 (internal shield on the spec sheet)?

[erwin_ve]

Question about EF86. What is the use of PIN 2 (internal shield on the spec sheet)?

You can ground pin2 and 7.

[rootz]

There are a couple of things that slightly concern me or lead to questions.
1) the 47k anode / 1k5 cathode resistor on the triode strapped EF86 would lead to a quiescent current of 2mA and a plate voltage of about 150V (or thereabouts). That's a bit of a stray from the usual 12ax7 setup you'd see in a Dumble. Is that anode resistor confirmed?
2) Same for the pentode. 240k anode, 1k5 cathode and 680k screen. Where would that land the quiescent current and voltage? I suspect much lower than the predicted 120V, more around 60V. So here also: are those resistor values all confirmed?
3) The 3m3 after the cathode follower seems strange to me. That would dump much of the signal through the reverb pot to ground. So much in fact, that it would be pretty much impossible to drive the PI sufficiently. You sure that 220k isn't at the output of the reverb pot?
4) Why would HAD load the recovery amp that already has a high output impedance with something like a 50k intensity pot? And instead use the CF to drive a 3m3 load through a 100n cap? So you have a 12au7 CF to drive the hardest load you could think of, but you use the anode of a 12ax7 instead...

I think the reverb would be taken from the volume pot. why would you otherwise need the pre driver for the 12at7 there? Is in line with the SSS too.I know this amp is one of a kind, but I'd expect to see some logic through all his amps though.

I think bottom line of all these questions is: how much is really confirmed, because some things pretty much puzzle me.

[sluckey]

Question about EF86. What is the use of PIN 2 (internal shield on the spec sheet)?

It's a tube shield that's inside the glass. Serves the same purpose as putting a tube shield on the outside of the glass. You need to connect it to ground for it to be effective. If left ungrounded it just acts like an antenna and will likely pick up all kinds of unwanted noise.

[Bombacaototal]

There are a couple of things that slightly concern me or lead to questions.
1) the 47k anode / 1k5 cathode resistor on the triode strapped EF86 would lead to a quiescent current of 2mA and a plate voltage of about 150V (or thereabouts). That's a bit of a stray from the usual 12ax7 setup you'd see in a Dumble. Is that anode resistor confirmed?
2) Same for the pentode. 240k anode, 1k5 cathode and 680k screen. Where would that land the quiescent current and voltage? I suspect much lower than the predicted 120V, more around 60V. So here also: are those resistor values all confirmed?
3) The 3m3 after the cathode follower seems strange to me. That would dump much of the signal through the reverb pot to ground. So much in fact, that it would be pretty much impossible to drive the PI sufficiently. You sure that 220k isn't at the output of the reverb pot?
4) Why would HAD load the recovery amp that already has a high output impedance with something like a 50k intensity pot? And instead use the CF to drive a 3m3 load through a 100n cap? So you have a 12au7 CF to drive the hardest load you could think of, but you use the anode of a 12ax7 instead...

I think the reverb would be taken from the volume pot. why would you otherwise need the pre driver for the 12at7 there? Is in line with the SSS too.I know this amp is one of a kind, but I'd expect to see some logic through all his amps though. Do you think it is placed elsewhere?

I think bottom line of all these questions is: how much is really confirmed, because some things pretty much puzzle me.

Thank you very much for taking the time rootz. As fas as your questions:
1) and 2) are confirmed in relation to layout and parts list. Whoever mapped the amp did a few mistakes for example on the plates of the PI which were mapped as 120R and are actually 120K. Therefore maybe similar mistakes have been made elsewhere
3) I originally had the 220K after the reverb return pot as per Fender. I moved it to the grid based on suggestions but I agree with you. It also makes more sense based on how this component was named on the parts list. Will move it back where I originally had it.
4) The tremolo is indeed AB763. The assumption is that it would be placed as a blackface amp. Do you think it is elsewhere?

I am not sure I follow the comment of the use of a 12AX7 anode instead

I agree on the reverb being taken from the volume pot. Bill’s schematic had it as per the green line which is why I included this option

Well, nothing is really confirmed, there is a parts list and some blurry gutshots, the rest is by association with what is already known

[talbany]

how much is really confirmed,

Rootz
None of it! Why? Because I have not been in the amp myself.
That or unless we see very detailed shots exposing most of the values of the components or a schematic from a reputable source and so far that just does not exist AFAIK. This amp has been very hush hush and nobody is talking!. Also given this amp is pretty much a one of a kind custom amp (Pentode front end and High voltage output section) for a particular musician makes it even more "impossible" to get very accurate info on. Even some hand drawn schematics that have come from very reputable and reliable sources contains some errors. As I have advised Bomba perhaps it would be wise to go back through HAD's other amps (SSS#002 0r 004) and cross those for clues since Dumble has been known to use the same type circuits in other amps (Reverb,PI driver LNFB)
BTW. Thanks for taking the time to study the amp and give us some technical insights!
I am sure there will be some tweaking needed after the amp is assembled.

I think the reverb would be taken from the volume pot.

Where does Dumble grab the signal for the reverb in 002?

SSS_002_revision_7_174 (5).pdf

The volume pot




Tony

[rootz]

I’d have to check the accuracy of my LTSpice EF86 models I use again. Last time I checked the curves were pretty much spot on the curves in the Philips datasheet. I hold the Ayumi models in high regard. Usually I’m not more than 5 to 10% max off when comparing sims to real life. I think the 240k anode resistor is wrong there. Must admit though that I need to draw some load lines in the datasheet to confirm what spice is telling me. Anyways, simmed my hifi amps too, 2x ef184 phase inverter and it was very accurate.

Busy day today, will look into the recent posts better when I get home.

By the way: anyone willing to do an accurate Visio layout, so we can compare to the blurry shots we have?

By the way 2: where is that parts list? I must have missed it somehow.

[Bombacaototal]

I’d have to check the accuracy of my LTSpice EF86 models I use again. Last time I checked the curves were pretty much spot on the curves in the Philips datasheet. I hold the Ayumi models in high regard. Usually I’m not more than 5 to 10% max off when comparing sims to real life. I think the 240k anode resistor is wrong there. Must admit though that I need to draw some load lines in the datasheet to confirm what spice is telling me. Anyways, simmed my hifi amps too, 2x ef184 phase inverter and it was very accurate.

Busy day today, will look into the recent posts better when I get home.

By the way: anyone willing to do an accurate Visio layout, so we can compare to the blurry shots we have?

By the way 2: where is that parts list? I must have missed it somehow.

Updated schematic below.

The parts list are on previous posts on this thread, there are some from Tony and some from me. I mapped all the parts and their respective numbers to my schematic.

I started the layour on .DIY, will share as soon as there is progress

[Bombacaototal]

Question about EF86. What is the use of PIN 2 (internal shield on the spec sheet)?

It's a tube shield that's inside the glass. Serves the same purpose as putting a tube shield on the outside of the glass. You need to connect it to ground for it to be effective. If left ungrounded it just acts like an antenna and will likely pick up all kinds of unwanted noise.

Thank you very much Erwin and Sluckey for the feedback, indeed very helpful

[Bombacaototal]

Pre amp board as I have it now (work in progress). You can use the numbers on my schematic to match the numbers on the blurry shots. If anyone wants to have a go at it and use Visio instead...I don't have a license

To keep in mind is that HAD used PCB and his connections are not as straight forward as a P2P (vide 001 as an example).

The blue lines are visible on the shots, the purple are pcb and connections not visible, both based on schematic.

[Aaron]

I've started editing the layout I did a while back. I haven't used Visio for a while, forgotten how time consuming it is! I swear it was quicker quicker to build
Still a work in progress, I think the 220k grid resistors at V2, V4 (reverb pre) and 10k V5 (reverb driver) are soldered to the valve base. I can't find them anywhere on the boards.
Power supply board is still very much a work in progress, too blurry to make out any details. Can just make out the wires at the top and the three bias capacitors.

Thanks,
Aaron

[Bombacaototal]

I've started editing the layout I did a while back. I haven't used Visio for a while, forgotten how time consuming it is! I swear it was quicker quicker to build
Still a work in progress, I think the 220k grid resistors at V2, V4 (reverb pre) and 10k V5 (reverb driver) are soldered to the valve base. I can't find them anywhere on the boards.
Power supply board is still very much a work in progress, too blurry to make out any details. Can just make out the wires at the top and the three bias capacitors.

Thanks,
Aaron

Fantastic Aaron, I am working on a version too and we can cross check at the end. I agree, it is quicker to build than doing those detailed layouts.

Also agree that the 220K grids (V2, V4a), the 220K after the reverb return and 10K (reverb driver) are on the valve as I cannot find them on the boards too.

[talbany]

I've started editing the layout I did a while back. I haven't used Visio for a while, forgotten how time consuming it is! I swear it was quicker quicker to build
Still a work in progress, I think the 220k grid resistors at V2, V4 (reverb pre) and 10k V5 (reverb driver) are soldered to the valve base. I can't find them anywhere on the boards.
Power supply board is still very much a work in progress, too blurry to make out any details. Can just make out the wires at the top and the three bias capacitors.

Thanks,
Aaron

Looks good Aaron! I don't know how accurate you want to draw that up but the resistors looks to be a combination of the Sprague Q-lines (tan) Phiers (RED) and Dale's RN65's (Plates) If you don't want to color every resistor maybe at least make a note on the Layout is always a nice touch This is the normal Dumble fare.
BTW. Visio layouts are very time consuming I know They are by far IMO the best looking! IMO!

Thanks
Tony

[Bombacaototal]

Tony, very interesting!

Just curious, which resistors are piher and which are q line? Dales are the plates obviously.
Maybe there is more than those black and white gut shots out there

Aaron, just a couple of things I picked up, on the tremolo the 100K and 10M are swapped (I think - because of where the cathodes ground is and where it probably meets the roach) and on the other side of the roach one of the legs is grounded. What is your view on the 47k at the bias network?