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

[Bombacaototal]

These parts right here. The ones you mentioned
.1 Dry Amp Screen Bypass Capacitor. 4x 220K called "Reverb Send Amp Feedback Serial Resistor", "Reverb Return Amp input terminating resistor", "Reverb return amp cathode resistor" and "Reverb Return Amp output.
I don't see these in green on your schematic or did you omit them because you don't know where they go? that's all I need to know

Tony

Tony, everything is already on the schematic and are not in green. The .01uF is on the pentode tube going to ground, and the 4x220K are already in the reverb circuit, one before the send triode, one after the rca return, one after the return pot and the "Reverb return amp cathode resistor" is actually a 2.2K cathode resistor (typo from whoever did the parts list - as per my previous post). I am fairly confident about those 220Ks. The only discrepancy with Bills schematic is the one after the return pot, which he puts after the .003uF

I hope it is clear...

[talbany]

These parts right here. The ones you mentioned
.1 Dry Amp Screen Bypass Capacitor. 4x 220K called "Reverb Send Amp Feedback Serial Resistor", "Reverb Return Amp input terminating resistor", "Reverb return amp cathode resistor" and "Reverb Return Amp output.
I don't see these in green on your schematic or did you omit them because you don't know where they go? that's all I need to know

Tony

Tony, everything is already on the schematic and are not in green. The .01uF is on the pentode tube going to ground, and the 4x220K are already in the reverb circuit, one before the send triode, one after the rca return, one after the return pot and the "Reverb return amp cathode resistor" is actually a 2.2K cathode resistor (typo from whoever did the parts list - as per my previous post). I am fairly confident about those 220Ks. The only discrepancy with Bills schematic is the one after the return pot, which he puts after the .003uF

I hope it is clear...

Yes all I wanted was to have them in highlighted some way so we are both looking at the same thing. It's Ok I got it now.
Thanks
Tony

[Bombacaototal]

I added everything to the schematic and all doubts and questions and missing values in green. I think it will make it easier for all

EDIT: Amended schematic further down the thread

[talbany]

I added everything to the schematic and all doubts and questions and missing values in green. I think it will make it easier for all

YES! Perfect thank you!

Generally when you have a part in question your asking about? put it where you think it goes highlight it 10K along with a ? That way we are both looking at the same thing. Will cross it with what I have
BTW.The 10K looks OK
1. I am not showing a .1 on the Dry amp on any of my schematics??
2.The only 1meg's I am showing are on each side of of the .01 like you have it. I am not an expert on trem's perhaps someone else might know what a Trem- Osc control resistor is?
3.The 220k is the grid resistor for the input to the mixer AFAIK
4. Not sure about the value of the dropper for the PI driver (unless it's the other 40K?). Shouldn't be difficult to figure that out after you get the supply up.
Tony

[Bombacaototal]

I added everything to the schematic and all doubts and questions and missing values in green. I think it will make it easier for all

YES! Perfect thank you!

Generally when you have a part in question your asking about? put it where you think it goes highlight it 10K along with a ? That way we are both looking at the same thing. Will cross it with what I have
BTW.The 10K looks OK
1. I am not showing a .1 on the Dry amp on any of my schematics??
2.The only 1meg's I am showing are on each side of of the .01 like you have it. I am not an expert on trem's perhaps someone else might know what a Trem- Osc control resistor is?
3.The 220k is the grid resistor for the input to the mixer AFAIK

Tony

Noted with thanks Tony. I made some further amendments to the schematic taking your suggestion into account. I coloured the resistors (10K, 30K) on the bias network at the PI as this is where I think they are but not 100% sure. I left the comment on the missing 47K.

Regarding the 10K on the Reverb driver the question was more relating to the LNFB. So I added another LNFB in green. I am not sure if the LNFB is before or after the 10K as I have seen HAD amps taking both approaches.

As far as the .1uF on the Pentode, it is indeed there, both on the parts list and also on the blurry gutshot. Electron makes mention about it too on his thread about the pentode amp. I am happy to put together some "evidence" shots if you would like.

The third 1 MEG on the tremolo is indeed puzzling. The 270K I coloured in green as this is where I think it is. Fender uses 390K there.

As far as topology, I think the entrance of the reverb is as per my black line. Most of the SSS amps use a 5751 on the driver circuit and having the AT7 there will already compensate for the difference in gain between a 12AX7 triode and the EF86 wired as triode. Also it has the matching LNFB and grid to the Pentode, which would indicate that this position makes sense

EDIT: Updated schematic further down the thread

[talbany]

Thanks for the revised schem. Don't know what to say about the .1 here is Electron's schematic he made of the amp. It's not there? Dunno.. Make it work

sss_preamp_schematic_239.pdf

Gotta roll for now will check back later.
BTW. I prefer a 12AT in driver for several reasons
Tony

[Bombacaototal]

Thanks for the revised schem. Don't know what to say about the .1 here is Electron's schematic he made of the amp. It's not there? Dunno.. Make it work

sss_preamp_schematic_239.pdf

Gotta roll for now will check back later.
BTW. I prefer a 12AT in driver for several reasons
Tony

As far as Electron, his schematic is wrong. If you follow the thread on the link below you will find his comment about the 0.1uF

https://ampgarage.com/forum/viewtopic.php?f=4&t=412

Only later on did I find out, that the second EF86 is wired as a pentode. The screen has a 0.1uF cap going to ground and a 680k resistor tapping of the B+ for the screen. Think standard Pentode stage.

And attached the parts list which make up the Pentode. I highlighted in yellow the 0.1uF we are talking about.

About the PI driver, my first thought was that the second 40K was its dropping resistor (if you look at other SSS amps, the dropping is always large, around 47K and tapped off the screens). And therefore it would make sense, but we would still be missing a supply capacitor (based on the parts list) to make this work

[sluckey]

The .1 screen bypass cap on V2 could be connected to ground or the cathode. Either would function the same.

There is no .1 on the screen in that hand drawn schematic because that pentode is strapped for triode operation, ie, screen connected to plate.

[Bombacaototal]

The .1 screen bypass cap on V2 could be connected to ground or the cathode. Either would function the same.

There is no .1 on the screen in that hand drawn schematic because that pentode is strapped for triode operation, ie, screen connected to plate.

Thanks Sluckey, I know we've been through this specific point before, but now that everything is open in the wild, I thought it would be fair to bring it back. Attached is the blurry board. Hard to tell which way it connects, cathode or ground. I added both lines in red to make it wasier to visualise.

And the supply of the tremolo is to be confirmed too. The plates need around 415V (probably same as the PI, and a safe bet would be to use the same). the VC- needs -50V. I wonder if the 1M will come around here to maybe drop the -150V to -50V? Based on how the parts list called the resistors, the 2.2M, 270K and 1M are around the same place and called "operation control resistor". ODS 121 (has SSS) does a two resistor network off C- to generate the VC- for the AB763 Tremolo. I would bet the 270K and 1M are there doing the same....

[Bombacaototal]

Schematic updated as per latest tremolo assumption.

Tony, yes probably the 220K is the grid of the mixer amp, and not a mixing resistor for the reverb. I moved this on the schematic.

Also I was going through my notes about the LNFB on the reverb, and everytime the LNFB was after the grid, the grid resistor was higher (15K, 33K, etc). All the ones that have 10K grid have the LNFB before the grid. I have also amended this.

EDIT: updated schematic further down the thread

[talbany]

Sounds Good!

BTW. I don't understand Electron say's it went to Gnd. Why the confusion?

keep at it.

Tony

[talbany]

Sounds Good!

BTW. I don't understand Electron say's it went to Gnd. Why the confusion? "Pentode"

keep at it.

Tony

[Bombacaototal]

Sounds Good!

BTW. I don't understand Electron say's it went to Gnd. Why the confusion?

keep at it.

Tony

Well, this was his assumption. As there were different possibilities I wanted to double check. But happy to keep at it. Updated.

We are nearly there...

EDIT: updated schematic further down the thread

[talbany]

Thanks for the info Tony. I wasn’t too far off with my guesstimates considering I only had the fuzzy photo copies and the preamp schematic.
The only missing piece of the puzzle was the mixing circuit. Might have to dig my build out and see if it makes much of a difference.
I really like the preamp in this amp. Crank that preamp volume to 10! I bought some 6U8A valves ages ago with the intention of doing a similar preamp with one valve.

You wouldn’t happen to have the resistor value sheet for the preamp?

Thanks,
Aaron

Hey Aaron
I pretty much posted everything I have on the Pentode as far as parts go but if I find something will pass it along
BTW.I have contemplated building this amp because of the preamp and touch sensitivity. I may still do it.
Sorry for the lateness as I just caught your post'

Tony

[talbany]

Sounds Good!

BTW. I don't understand Electron say's it went to Gnd. Why the confusion?

keep at it.

Tony

Well, this was his assumption. As there were different possibilities I wanted to double check. But happy to keep at it. Updated.

We are nearly there...

Just so you know I just looked over the schematic real quick and as far as what Dumble used and where? that's about it. (You know as much as I do) so if anyone else wants to jump in and provide any more technical info to make everything operate correctly have at it. Will try to keep up with the build

Good Luck
Tony