s-petersen
Scott
What is that amp? looks pretty interesting
Parts and Pieces: A True ARC Mystery
- Thread starter dcgillespie
- Start date
nj pheonix
Lunatic Member
It was an atmas-sphere s-30
OTL
s-petersen
Scott
Cool!
Planning is everything, even if it's just the AC power wiring. The IEC connector is designed to use push-on spade terminals -- except there's no room for them and the board when installed. So, as part of the chassis pre--wiring process, the leads to the connector are soldered to it, coming down to the terminals from running along the underside of the chassis deck. Up towards the front of the chassis, a hole in the side of the chassis provided there serves to mount a stud that firmly asfixes a lock washer ground lug to the chassis, to provide a secure chassis connection for the AC power ground lead. That's about the only way I know of to make a good ground connection to an anodized aluminum chassis that I know of, as the anodized surface doesn't conduct electricity, and of course you can't solder to it, so you need something that will cut through the anodized surface, which the lock washer does. The stud is long enough that after a jam nut is installed, a cable clamp is installed to hold the AC Power cord in place, and finally a T-Strip is installed to facilitate the AC power wiring, connections to the dual primary winding leads from the power transformer, the 30A soft start relay, and the dual thermistor leads.
Not shown, the AC Power mini-switch has also been removed to pre-wire it, since there is virtually no access to its terminals once installed (hidden by the power transformer leads). The LED indicator lamps will need to be pre-wired as well.
The output terminals also have to be pre-wired, and I can do that for the right channel terminals, but I'm still waiting on the material to come in to make the block that the terminals mount on for the left channel. So, once the pre-wiring I can do is done, then the project goes on hold until that material arrives, the blocks are then made, and the new board/with terminals is installed. After those terminals are pre-wired, then the board can be installed permanently, and the final wiring started. The final wiring will be quite a chore in and off itself as there are lots of leads already installed needing to interconnect with off board items, and more leads yet to be installed for the same purpose.
Sometimes on the schematics I draw and post, I am asked why I show the core of the OPT grounded. I do this because #1 it is by virtue of its mounting and #2, because grounding the core represents best practice shielding wise. So..... that's all out the window with this amplifier. The OPTs are both mounted on insulated washers, and secured by hardware that is insulated from the chassis as well. There is infinite resistance between the stack bolts and the chassis, or the lams, cover, and chassis. Now this should be interesting........... On the other hand, the power transformer (which has no bottom end bell) has the bottom most lam mounted directly against the top of the chassis deck, and on the underside, a fiber washer is placed first, then a steel washer, and finally a nut on each of the four mounting studs. Measurement between the stack bolts and chassis indicates a couple of Ohms resistance. The OPT mounting appears to be what it is, what it is, what is is. But I'm really questioning if this is standard power transformer mounting practice by ARC. I would think they would at least have stack bolt tightening nuts screwed onto the transformer mounting studs first before the transformer is set into the chassis, providing a space that is the thickness of that nut between the bottom most lam, and the top of the chassis deck (this is how the OPTs are installed). On the other hand, doing so means that the power transformer will sit higher than the OPTs (by the thickness of the extra nut), where as currently, the top of all three transformers represent the same height from the chassis deck as currently mounted. If there's anyone with a similar period ARC product (it doesn't have to be a D115) that could take a look and see if this is how their power transformer is mount and report back, it would be greatly appreciated!!
Dave
The apparent scratches aren't scratches at all and easily rub off, being what appears to be a surface residue from the anodizing process.......
Not shown, the AC Power mini-switch has also been removed to pre-wire it, since there is virtually no access to its terminals once installed (hidden by the power transformer leads). The LED indicator lamps will need to be pre-wired as well.
The output terminals also have to be pre-wired, and I can do that for the right channel terminals, but I'm still waiting on the material to come in to make the block that the terminals mount on for the left channel. So, once the pre-wiring I can do is done, then the project goes on hold until that material arrives, the blocks are then made, and the new board/with terminals is installed. After those terminals are pre-wired, then the board can be installed permanently, and the final wiring started. The final wiring will be quite a chore in and off itself as there are lots of leads already installed needing to interconnect with off board items, and more leads yet to be installed for the same purpose.
Sometimes on the schematics I draw and post, I am asked why I show the core of the OPT grounded. I do this because #1 it is by virtue of its mounting and #2, because grounding the core represents best practice shielding wise. So..... that's all out the window with this amplifier. The OPTs are both mounted on insulated washers, and secured by hardware that is insulated from the chassis as well. There is infinite resistance between the stack bolts and the chassis, or the lams, cover, and chassis. Now this should be interesting........... On the other hand, the power transformer (which has no bottom end bell) has the bottom most lam mounted directly against the top of the chassis deck, and on the underside, a fiber washer is placed first, then a steel washer, and finally a nut on each of the four mounting studs. Measurement between the stack bolts and chassis indicates a couple of Ohms resistance. The OPT mounting appears to be what it is, what it is, what is is. But I'm really questioning if this is standard power transformer mounting practice by ARC. I would think they would at least have stack bolt tightening nuts screwed onto the transformer mounting studs first before the transformer is set into the chassis, providing a space that is the thickness of that nut between the bottom most lam, and the top of the chassis deck (this is how the OPTs are installed). On the other hand, doing so means that the power transformer will sit higher than the OPTs (by the thickness of the extra nut), where as currently, the top of all three transformers represent the same height from the chassis deck as currently mounted. If there's anyone with a similar period ARC product (it doesn't have to be a D115) that could take a look and see if this is how their power transformer is mount and report back, it would be greatly appreciated!!
Dave
The apparent scratches aren't scratches at all and easily rub off, being what appears to be a surface residue from the anodizing process.......
nj pheonix
Lunatic Member
Dave,
I'm not sure i can see it or if you provided a pic where the spade connections are.
I know they make 90° female spade connectors.
I don't know if that'd be a solution or not. I just thought it might be a possible option.
I may have access to some . What is the wire size?
I'm not sure i can see it or if you provided a pic where the spade connections are.
I know they make 90° female spade connectors.
I don't know if that'd be a solution or not. I just thought it might be a possible option.
I may have access to some . What is the wire size?
I have seen those connectors you're describing, but didn't think about them as an option, so I went ahead and just soldered the wires to the IEC connector's terminals. I don't know that the 90˚ type are readily available at local hardware or big-box home stores, but next time, I'll know! Thanks for the tip! (Oh, and the wire size is 16 gauge)
Dave
Dave
nj pheonix
Lunatic Member
If i find some I'll mail them to you for your junk box
Gerry Lynch
Active Member
transformer
Output transformer
there are nuts under the power transformer but of the output...
So yours is almost the exact opposite of mine? Sheesh. Your power transformer mounting makes much more sense however, since with the fiber washers on top of the chassis, and only 4 contact points via the mounting studs, it makes much more sense as a quieter way of mounting the transformer than the one on my chassis is mounted. With my transformer sitting right on the chassis, it hums notably even with no load on it when powered up, so I'll change that around now before any leads get connected. Maybe it just hasn't learned the words yet...........
Dave
BTW -- I forgot to thank you for posting the pic of your amp, so thanks! Which model is it?
Dave
BTW -- I forgot to thank you for posting the pic of your amp, so thanks! Which model is it?
Last edited:
Gerry Lynch
Active Member
I like star washers for this. More points of contact vs a standard split lock washer.
^ Absolutely. That's the type that the lock washer grounding lug is.
After seeing the pic of Gerry's amp, I looked around on the web for more pics of the D115 and yep, the top of the power transformer is notably higher than the top of the OPTs on regular production models, meaning the intention was for there to be (at least) a stack tightening nut (with appropriate washers) on the transformer studs before it was to be mounted into the chassis. In my chassis, the bottom lam sat right on the chassis deck, with the steel and fiber washer seen on the top of the chassis in Gerry's pic (that the transformer sits on) mounted on the bottom side. This made the transformers all look level from a height perspective, but is clearly not the way the power transformer was meant to me mounted, and no doubt allowed the chassis to magnify the hum of the transformer. I've now removed the power transformer, found some appropriate nylon and steel washers and nuts to secure the studs in the transformer, and will then remount it in the chassis using the steel and fiber washers originally used below the chassis for the transformer to sit on on top of the chassis. New steel flat washers and star lock washers will be used used on the underside to secure the transformer to the chassis. There is no continuity between any of the transformer studs, or between any of the studs and the lams. I am surely glad this got address before the transformer was all wired up -- this sucker has 22 leads to it. Details, details. But, it's what should allow the finished piece to be as close to the real thing as possible.........
Dave
Below: Much better!
After seeing the pic of Gerry's amp, I looked around on the web for more pics of the D115 and yep, the top of the power transformer is notably higher than the top of the OPTs on regular production models, meaning the intention was for there to be (at least) a stack tightening nut (with appropriate washers) on the transformer studs before it was to be mounted into the chassis. In my chassis, the bottom lam sat right on the chassis deck, with the steel and fiber washer seen on the top of the chassis in Gerry's pic (that the transformer sits on) mounted on the bottom side. This made the transformers all look level from a height perspective, but is clearly not the way the power transformer was meant to me mounted, and no doubt allowed the chassis to magnify the hum of the transformer. I've now removed the power transformer, found some appropriate nylon and steel washers and nuts to secure the studs in the transformer, and will then remount it in the chassis using the steel and fiber washers originally used below the chassis for the transformer to sit on on top of the chassis. New steel flat washers and star lock washers will be used used on the underside to secure the transformer to the chassis. There is no continuity between any of the transformer studs, or between any of the studs and the lams. I am surely glad this got address before the transformer was all wired up -- this sucker has 22 leads to it. Details, details. But, it's what should allow the finished piece to be as close to the real thing as possible.........
Dave
Below: Much better!
With the transformer reinstalled now, the transformer definitely sits higher off the chassis deck now just as it does in regular production models, and maybe even just a pinch higher than in the production units (maybe about 1/16th of an inch). Nothing of any significance at all, and no doubt due to to the thickness of the washers I used versus those used by the factory, or maybe they used fiber washers on the bottom side of the transformer rather than the nylon washers I used, or no steel washers, who knows. But now, each mount screw has very good electrical contact with the chassis, but no contact with the lams at all, so all should be good to go.
From the additional picture hunting for power transformer mounting details, I've also determined that the cage cover I have is in fact that for a D115. So that little detail has been determined now too. Holes in the chassis don't all line up with all of those in the cage cover -- not because it's the wrong cage, but because it's the wrong chassis, which we knew early on from nearly the get-go. As it stands now then, the only thing that isn't a bonafide D115 MK II piece, is the chassis, and the separate little driver regulator board -- both of which are being made to work in spite of being the wrong piece. The front panel, transformers, main board, and cage cover however, are all the real thing. Little by little it's coming together.........
Dave
From the additional picture hunting for power transformer mounting details, I've also determined that the cage cover I have is in fact that for a D115. So that little detail has been determined now too. Holes in the chassis don't all line up with all of those in the cage cover -- not because it's the wrong cage, but because it's the wrong chassis, which we knew early on from nearly the get-go. As it stands now then, the only thing that isn't a bonafide D115 MK II piece, is the chassis, and the separate little driver regulator board -- both of which are being made to work in spite of being the wrong piece. The front panel, transformers, main board, and cage cover however, are all the real thing. Little by little it's coming together.........
Dave
Progress, But More Circuit Board Issues:
1. Eyelet #57 is shown two places on the board:
At one place it is representing the 335 volt output of the screen grid regulator (which makes for yet another clue that this is an original D115 board and NOT what is more and more appearing to be a production MK II board produced for those units, since the output of the screen regulator in the MK II is 312 vdc (but I've configured the board with the MK II design anyway):
While at this point, it is representing the ground trace of the DC heater supply. Whoops......:
Of course, it doesn't help any that eyelet #57 isn't shown anywhere on the schematic. In fact most of the fifty-something number eyelets on the schematics are either missing, misnumbered, or representing the entirely wrong trace........... Details, details.
And then there's this: Caps installed that are operating continuously over rated voltage:
This one, and the one above it operate at at a continuous 430 vdc:
This 5.0 uF cap operates at at least 200 vdc, and no doubt more with today's line voltages:
The eight output tube coupling caps are routinely subjected to about 500 volts during startup, but are only rated for 400 volts. MK II amplifiers installed 450 volt components which is better, but are still underrated. Could contribute to some of the documented spectacular ARC meltdown events......
Proper caps are on order, as are the two green LEDs (although personally I like red for the screen indicator). Also still waiting on the power relay, and the material to make the second output terminal strip board.
Progress has continued however. The chassis AC wiring is done, with the board confirmed to fit. It's a good thing the wiring to the IEC connector was ultimately soldered to its terminals -- there is NO room for any kind of push on Spade terminal -- angled or otherwise. The wiring for the power transformer itself had to be relocated from where it is located in a production D115 because the extra wiring for the dual primary transformer interfered with any attempt to install the board. As redone, it is now well out of the way, with easy provision to change the winding connections for different voltage sources if needed.
Based on the date on the board (1983), the eyelet labeling error, the fact that the board supports the original design driver circuit (extra components), and the incorrect (for the MK II) screen voltage indicator on the board (which is correct for the original design), I think it's a done deal to say that this is an original D115 board, and that there was in fact very likely a MK II board that superseded it when that version came out. More details are falling into place as to the items that actually make up this amplifier.......
Dave
1. Eyelet #57 is shown two places on the board:
At one place it is representing the 335 volt output of the screen grid regulator (which makes for yet another clue that this is an original D115 board and NOT what is more and more appearing to be a production MK II board produced for those units, since the output of the screen regulator in the MK II is 312 vdc (but I've configured the board with the MK II design anyway):
While at this point, it is representing the ground trace of the DC heater supply. Whoops......:
Of course, it doesn't help any that eyelet #57 isn't shown anywhere on the schematic. In fact most of the fifty-something number eyelets on the schematics are either missing, misnumbered, or representing the entirely wrong trace........... Details, details.
And then there's this: Caps installed that are operating continuously over rated voltage:
This one, and the one above it operate at at a continuous 430 vdc:
This 5.0 uF cap operates at at least 200 vdc, and no doubt more with today's line voltages:
The eight output tube coupling caps are routinely subjected to about 500 volts during startup, but are only rated for 400 volts. MK II amplifiers installed 450 volt components which is better, but are still underrated. Could contribute to some of the documented spectacular ARC meltdown events......
Proper caps are on order, as are the two green LEDs (although personally I like red for the screen indicator). Also still waiting on the power relay, and the material to make the second output terminal strip board.
Progress has continued however. The chassis AC wiring is done, with the board confirmed to fit. It's a good thing the wiring to the IEC connector was ultimately soldered to its terminals -- there is NO room for any kind of push on Spade terminal -- angled or otherwise. The wiring for the power transformer itself had to be relocated from where it is located in a production D115 because the extra wiring for the dual primary transformer interfered with any attempt to install the board. As redone, it is now well out of the way, with easy provision to change the winding connections for different voltage sources if needed.
Based on the date on the board (1983), the eyelet labeling error, the fact that the board supports the original design driver circuit (extra components), and the incorrect (for the MK II) screen voltage indicator on the board (which is correct for the original design), I think it's a done deal to say that this is an original D115 board, and that there was in fact very likely a MK II board that superseded it when that version came out. More details are falling into place as to the items that actually make up this amplifier.......
Dave
Progress --
Still waiting on the 4 mm black plexiglass to make the other output terminal strip and the power relay to arrive, but other than that, all other parts have arrived. In the mean time, the power switch, two LEDs, and the AC power fuse post have all been either wired or pre-wired and installed:
On the top side, the board pre-wiring has been done for the other three large electrolytic caps. The two caps nearest the front of the chassis can't be installed and connected into the circuit until the board itself is permanently installed. Otherwise they interfere with the installation/removal of the board. The board at this point is just mounted in place with a couple of screws to facilitate pre-wiring of the board for output transformer and electrolytic cap connections:
On the underside, this is no Eico or Heathkit project! The board will now be removed yet again, since all the board pre-wiring (i.e., wiring to those board connections that that cannot be made to it once it, or the large electrolytic caps on it are fully installed) is now finished. With it removed, things really come to a halt quickly then until the plexiglass and power relay come in. When they do, the relay will be mounted, the other speaker terminal board made, installed, and prewired, and then the board will be installed for good. When it is, connecting this maze of spaghetti, and making a couple of small boards to mount the input jacks on (that will cover the large holes for the Cannon input jacks originally intended to be mounted on this chassis) are all that remain to finish the amplifier. Yeah, lots of tests to run to ensure this puppy rumbles to life safely and properly, but there is definitely light at the end of the tunnel now.
Also note that the two power supply caps that operate consistently over the 400 volt rating of the original caps installed have now been replaced as well, with yellow Nichicon 630 volt pieces. They were particularly hard to replace, since both leads of these caps connect to very large traces on both sides of the board, that simply suck the heat out of even my 140 watt Weller gun. The other caps identified for replacement I am currently pondering. Polypropylene caps are self healing, so that any damage incurred during the short turn on process heals itself -- if in fact any damage is even done. I note that on later models of the D115, the coupling caps were upgraded to 450 volt pieces -- which is still exceeded during turn on. So, I'm still looking into this. They will be much much easier to replace however, since none are soldered to large traces on both sides of the board. Under the maze of power transformer wires, the small driver stage regulator board is also installed (permanently) now.
Slowly but surely........
Dave
Still waiting on the 4 mm black plexiglass to make the other output terminal strip and the power relay to arrive, but other than that, all other parts have arrived. In the mean time, the power switch, two LEDs, and the AC power fuse post have all been either wired or pre-wired and installed:
On the top side, the board pre-wiring has been done for the other three large electrolytic caps. The two caps nearest the front of the chassis can't be installed and connected into the circuit until the board itself is permanently installed. Otherwise they interfere with the installation/removal of the board. The board at this point is just mounted in place with a couple of screws to facilitate pre-wiring of the board for output transformer and electrolytic cap connections:
On the underside, this is no Eico or Heathkit project! The board will now be removed yet again, since all the board pre-wiring (i.e., wiring to those board connections that that cannot be made to it once it, or the large electrolytic caps on it are fully installed) is now finished. With it removed, things really come to a halt quickly then until the plexiglass and power relay come in. When they do, the relay will be mounted, the other speaker terminal board made, installed, and prewired, and then the board will be installed for good. When it is, connecting this maze of spaghetti, and making a couple of small boards to mount the input jacks on (that will cover the large holes for the Cannon input jacks originally intended to be mounted on this chassis) are all that remain to finish the amplifier. Yeah, lots of tests to run to ensure this puppy rumbles to life safely and properly, but there is definitely light at the end of the tunnel now.
Also note that the two power supply caps that operate consistently over the 400 volt rating of the original caps installed have now been replaced as well, with yellow Nichicon 630 volt pieces. They were particularly hard to replace, since both leads of these caps connect to very large traces on both sides of the board, that simply suck the heat out of even my 140 watt Weller gun. The other caps identified for replacement I am currently pondering. Polypropylene caps are self healing, so that any damage incurred during the short turn on process heals itself -- if in fact any damage is even done. I note that on later models of the D115, the coupling caps were upgraded to 450 volt pieces -- which is still exceeded during turn on. So, I'm still looking into this. They will be much much easier to replace however, since none are soldered to large traces on both sides of the board. Under the maze of power transformer wires, the small driver stage regulator board is also installed (permanently) now.
Slowly but surely........
Dave
Scrapin' the bottom of the barrel for any more forward progress:
Below: Little plates have been made to facilitate mounting conventional RCA input jacks where the Cannon input connectors were originally supposed to mount. The input impedance information is wrong as now the unit (obviously) has unbalanced RCA input jacks, and standard D115 input impedance (specified as 75KΩ, but more like 70KΩ in reality). The D115 featured level controls which I've never been a big fan of, and without any real space for them anyway, I am wiring the unit as if the level controls were electrically installed, and turned up full.
Below: In addition to the two power supply caps that were continuously operating over rated voltage, I have also changed out the 8 output tube 400 volt coupling caps that are routinely subjected to 500 volts at turn on. The film caps installed are self healing, meaning that if they arc internally, any deformity created in the film repairs itself over time. If this only occurs very infrequently, that's one thing. But if it potentially happens with regularity at turn on, that's quite another. Since these are output tube couplers, and ARC amplifiers have been noted for their output tube blow ups, I decided to replace these caps with fresh Nichicon 630 volt caps of the same value to completely eliminate these caps from possibly contributing to any such antisocial output tube behavior should it occur.
A couple more small things I can do (prewire the input jacks and add terminals to the new leads installed for the two remaining large electrolytic caps that get installed after the board is installed), and then the entire project will need to be set aside until the power relay and/or 4 mm black plexiglass arrive to make the remaining rear terminal board. Once that is done and the terminal board prewired, then the final assembly can commence: the board is permanently installed, the maze of wires connected, and the completed unit testing begun.
Dave
Below: Little plates have been made to facilitate mounting conventional RCA input jacks where the Cannon input connectors were originally supposed to mount. The input impedance information is wrong as now the unit (obviously) has unbalanced RCA input jacks, and standard D115 input impedance (specified as 75KΩ, but more like 70KΩ in reality). The D115 featured level controls which I've never been a big fan of, and without any real space for them anyway, I am wiring the unit as if the level controls were electrically installed, and turned up full.
Below: In addition to the two power supply caps that were continuously operating over rated voltage, I have also changed out the 8 output tube 400 volt coupling caps that are routinely subjected to 500 volts at turn on. The film caps installed are self healing, meaning that if they arc internally, any deformity created in the film repairs itself over time. If this only occurs very infrequently, that's one thing. But if it potentially happens with regularity at turn on, that's quite another. Since these are output tube couplers, and ARC amplifiers have been noted for their output tube blow ups, I decided to replace these caps with fresh Nichicon 630 volt caps of the same value to completely eliminate these caps from possibly contributing to any such antisocial output tube behavior should it occur.
A couple more small things I can do (prewire the input jacks and add terminals to the new leads installed for the two remaining large electrolytic caps that get installed after the board is installed), and then the entire project will need to be set aside until the power relay and/or 4 mm black plexiglass arrive to make the remaining rear terminal board. Once that is done and the terminal board prewired, then the final assembly can commence: the board is permanently installed, the maze of wires connected, and the completed unit testing begun.
Dave
I tell you gadget, overall it's been an enjoyable and certainly challenging project, but sometimes the never ending detail issues to address -- even in performing normal service on a regular production D115 let alone trying to stuff one with such a screwed up board into a smaller chassis -- could drive me to drink. At this point then, I'll take all the humor I can get!...........
Dave
Dave
nj pheonix
Lunatic Member
Do mind if i ask?
It seems there's a fair amount of dressed wiring (routed and ty wrapped).
Is this because of the nature or what it is? (An enigma of sorts?) Or would a production unit have that as well?
Oh commenting of the caps, its sort of a mystery to me that ARC would use the underated caps in the first place
It seems there's a fair amount of dressed wiring (routed and ty wrapped).
Is this because of the nature or what it is? (An enigma of sorts?) Or would a production unit have that as well?
Oh commenting of the caps, its sort of a mystery to me that ARC would use the underated caps in the first place