MiKro Posted September 7, 2020 Report Share Posted September 7, 2020 I sold my old Carvin X100B head some years back to a friend. It is now in need of re-capping all of the electrolytic capacitors and needs a new set of tubes. While IN there I am re-flowing all of the solder joints to make sure no cold solder joint and I will be adding an adjustable bias pot. So while I have been cleaning, I might as well do this at the same time. LOL Just ordered more parts today as I did not have any NP 10uf 50v caps. . I have polarized not any Non-polarized. Damn!! Some pics of the 1989 board. once done I will do a good cleanup and get rid of excess flux. LOL It was updated to 93 standards as the tech I used made some changes. The power caps removed The old ones, still more to change out. The new ones 1 Quote Link to comment Share on other sites More sharing options...
Bizman62 Posted September 8, 2020 Report Share Posted September 8, 2020 The new caps look like of a much higher quality! 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 8, 2020 Author Report Share Posted September 8, 2020 8 hours ago, Bizman62 said: The new caps look like of a much higher quality! They are much better audio quality caps. That and a new set of Mullard Tubes vs the old GT tubes and a slightly cooler Bias setting should really make this sweet sounding. My only issue is the pots I need are not available until after the first of the year. They are very scratchy and deoxit is not cleaning them very well anymore. So they will need replacing as well. MK Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 8, 2020 Author Report Share Posted September 8, 2020 I made the adjustable bias board today that I will be adding on. A very simple device that will replace one of the resistors in the voltage divider for the grids of the power tubes. mk Here is a closeup of the schematic area that I am changing using this little addon I made. 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 8, 2020 Author Report Share Posted September 8, 2020 So the 10uf 50v NP/BP caps came in today. Even though they are Non-Polarized/Bipolar, I need to put them on the scope to find the cathode so I can put the shielded side of the cap going the correct direction for the best audio. MK 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 18, 2020 Author Report Share Posted September 18, 2020 All of the electrolytic caps are now replaced. Adjustable bias part I made is wired in place. Pots are cleaned. Now to reinstall this and check /set the bias with the new tubes. Oh boy such fun. LOL!!! MK update: I finally found some pots that I can use. They are not for PCB but I can wire direct to the board so that will fix any problems as far as the pots go. I will need to add 2 additional standoffs to support the board since the pots were the front support in the chassis face. I would rather do this now than have to pull it out later to change them as I know some are on the verge of being very questionable as far as working properly. I have used deoxit over the years and it was becoming less and less effective. LOL 2 Quote Link to comment Share on other sites More sharing options...
curtisa Posted September 18, 2020 Report Share Posted September 18, 2020 On 9/9/2020 at 6:36 AM, MiKro said: Even though they are Non-Polarized/Bipolar, I need to put them on the scope to find the cathode so I can put the shielded side of the cap going the correct direction for the best audio. Interesting. What's your thinking with regards to doing this kind of testing for bipolar capacitors? Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 18, 2020 Author Report Share Posted September 18, 2020 20 minutes ago, curtisa said: Interesting. What's your thinking with regards to doing this kind of testing for bipolar capacitors? They are still caps and being such they are built with an outer foil/shield just like most caps are. It is not as defined ( lack of better words) but it is still there. If you test caps with an oscillascope you will find they all have a negative and a positive side to them based on EMI influence. that being said the foil/shield/ neg side should go to ground of circuit flow. Even Orange drops and other types this is common. Also if you rely on the marking of a cap for negative you may be wrong as many test show that they just go thru a machine and the band is applied with no real reference to the actual construction of the cap. Here is a great video that explains it more. Caps in backwards? Video mk 1 Quote Link to comment Share on other sites More sharing options...
curtisa Posted September 18, 2020 Report Share Posted September 18, 2020 I was actually just watching that video - the stars must have aligned There was a white paper written some time ago by an application engineer at SBE Electronics (which used to be Sprague, who made the orange drops) regarding this very topic. The crux of their explanation was that the manufacturing processes at SBE/Sprague could never distinguish the outer foil location of their caps, and the black line is not an indicator of the outermost layer location. He doesn't go into exactly what the black line was used to signify which perhaps muddies the waters a bit, but anyway... Further, the theory that the outer layer must be grounded, or at least connected to the side of the circuit that has the lower impedance, starts to fall apart when you consider what the impedance of that capacitor is in the context of the circuit around it. 10uF at 60Hz is an impedance of about 260 ohms, which is significantly smaller than the resistance of, say the parallel cathode biasing resistor of a tube stage or the input impedance of the next stage of an opamp (I'm assuming the intended application of your caps in the X100B a bit here). The impedance of the cap is so low at frequencies of interest that the potential for coupling external noise is practically identical irrespective of which way around it is installed in the circuit. Long story short, the implication was to not worry too much about trying to determine a correct way to install the capacitor with regards to the outermost foil layer. 2 Quote Link to comment Share on other sites More sharing options...
Prostheta Posted September 19, 2020 Report Share Posted September 19, 2020 I'd say that it's worthwhile putting silastic or similar appropriate elastomer on your caps to dampen vibrations. Mostly mechanical, however I suppose you could argue for the audio also. Either way, get some in there. 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 19, 2020 Author Report Share Posted September 19, 2020 6 hours ago, Prostheta said: I'd say that it's worthwhile putting silastic or similar appropriate elastomer on your caps to dampen vibrations. Mostly mechanical, however I suppose you could argue for the audio also. Either way, get some in there. Already on the things to do. I could not find my tube of silicone so I have to buy another. LOL MK 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 19, 2020 Author Report Share Posted September 19, 2020 15 hours ago, curtisa said: I was actually just watching that video - the stars must have aligned There was a white paper written some time ago by an application engineer at SBE Electronics (which used to be Sprague, who made the orange drops) regarding this very topic. The crux of their explanation was that the manufacturing processes at SBE/Sprague could never distinguish the outer foil location of their caps, and the black line is not an indicator of the outermost layer location. He doesn't go into exactly what the black line was used to signify which perhaps muddies the waters a bit, but anyway... Further, the theory that the outer layer must be grounded, or at least connected to the side of the circuit that has the lower impedance, starts to fall apart when you consider what the impedance of that capacitor is in the context of the circuit around it. 10uF at 60Hz is an impedance of about 260 ohms, which is significantly smaller than the resistance of, say the parallel cathode biasing resistor of a tube stage or the input impedance of the next stage of an opamp (I'm assuming the intended application of your caps in the X100B a bit here). The impedance of the cap is so low at frequencies of interest that the potential for coupling external noise is practically identical irrespective of which way around it is installed in the circuit. Long story short, the implication was to not worry too much about trying to determine a correct way to install the capacitor with regards to the outermost foil layer. I agree Andrew. Still if it might help, it is worth the extra few minutes to align it properly. MK 1 Quote Link to comment Share on other sites More sharing options...
Prostheta Posted September 19, 2020 Report Share Posted September 19, 2020 Even bloody minded people like me can't resist aligning things for no good reason. Humans are stupid. I want a refund. 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 19, 2020 Author Report Share Posted September 19, 2020 40 minutes ago, Prostheta said: Even bloody minded people like me can't resist aligning things for no good reason. Humans are stupid. I want a refund. You are too funny. ::) 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 20, 2020 Author Report Share Posted September 20, 2020 So today I pulled all of the pots off the board. What a PITA that was. the push/pulls had 9 connections. F"me. LOL Waiting on so new ones that are not PCB mount so I will wire them to the board. Ones that were PCB would be next year before I could get them. I will have to add 2 stand offs on the board in the front to hold it in place. No big deal as it already has holes for that as does the chassis. MK 1 Quote Link to comment Share on other sites More sharing options...
Prostheta Posted September 21, 2020 Report Share Posted September 21, 2020 I imagine that those old PCBs easily fry and lose tracks and pads. Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 21, 2020 Author Report Share Posted September 21, 2020 11 hours ago, Prostheta said: I imagine that those old PCBs easily fry and lose tracks and pads. They are not fun. This one actually has decent traces and pads. mk 1 Quote Link to comment Share on other sites More sharing options...
Prostheta Posted September 21, 2020 Report Share Posted September 21, 2020 Probably heavier oz copper, or at least not light anyway. Those cement box resistors can throw out some heat. What ICs are on there? I'm guessing there'll be a few vanilla op-amps kicking around like NE5532s. It might be good to upgrade those, or at least that's the sort of pointless fiddling I'd do. They're socketed, which is always a good sign. Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 21, 2020 Author Report Share Posted September 21, 2020 34 minutes ago, Prostheta said: Probably heavier oz copper, or at least not light anyway. Those cement box resistors can throw out some heat. What ICs are on there? I'm guessing there'll be a few vanilla op-amps kicking around like NE5532s. It might be good to upgrade those, or at least that's the sort of pointless fiddling I'd do. They're socketed, which is always a good sign. I didn't even look at those to be honest. LOL. All I want to do is fix the snap crackle pop. LOL. The pots were very suspect as was also the electrolytics. I know the Power tubes are very old so they need replacing, so I decided to change them all out including new preamp tubes. This should bring this amp up too almost new. Will see what it sounds like when I am done? The trannies test out okay. The only thing left to do if still any problems will be to look at the polyfilm caps and transistors. Hopefully they are not an issue. Looking at the schematics they say that All of the Op-Amps are 4558 TYPE. MK 1 Quote Link to comment Share on other sites More sharing options...
Prostheta Posted September 21, 2020 Report Share Posted September 21, 2020 Oh fffuuuu. They're terrible. Swap them out for something simple but better like a JFET TL072. The 4558 topology is ancient 70s stuff, and pretty low tech. OPA2134 would be the gold standard I guess, but even an NE5532 would be better than a 4558. OPA2134s suck up a bit more current, but in an amp like that it's a fart in a windstorm. TL072 is cheap, easy to acquire and a straight swap. 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 21, 2020 Author Report Share Posted September 21, 2020 22 minutes ago, Prostheta said: Oh fffuuuu. They're terrible. Swap them out for something simple but better like a JFET TL072. The 4558 topology is ancient 70s stuff, and pretty low tech. OPA2134 would be the gold standard I guess, but even an NE5532 would be better than a 4558. OPA2134s suck up a bit more current, but in an amp like that it's a fart in a windstorm. TL072 is cheap, easy to acquire and a straight swap. At this point I just want to be done with it. LOL. They are working fine So I plan to move forward. I agree there are better but I am not going to go that way currently. Thanks for the suggestions Carl. MK 1 Quote Link to comment Share on other sites More sharing options...
Prostheta Posted September 21, 2020 Report Share Posted September 21, 2020 NP - have at it! 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 21, 2020 Author Report Share Posted September 21, 2020 SoI had a tech back in the mid 90s look at this. I suspect he was the flux culprit in to this thing and renewed the necessary parts. I am finding that his cleaning skills of flux sucked. One more thing I have to do. First though my power resistors look okay , no cracks in them but what appears to be Soldering iron burn marks? Again the old tech? Now the 10 watt resistor though has 3 cracks in it. So I think I will replace that one. LOL!! MK 1 Quote Link to comment Share on other sites More sharing options...
Prostheta Posted September 22, 2020 Report Share Posted September 22, 2020 The joint on the cracked 10W resistor looks very poor also. Perhaps he missed with the flux by about an inch, " ±10%"? 1 Quote Link to comment Share on other sites More sharing options...
MiKro Posted September 22, 2020 Author Report Share Posted September 22, 2020 13 hours ago, Prostheta said: The joint on the cracked 10W resistor looks very poor also. Perhaps he missed with the flux by about an inch, " ±10%"? LOL, Yep It will be replaced. I am searching for a hum source while I am in this. I am beginning to think it may be the heater wiring. Or actually the lack of where they used traces instead. There was always a Hum in this amp back when I owned it? I always thought it was my home and its old wiring. Now with a better understanding of these things I am beginning to suspect differently. Al of the AC wiring to the tubes are just bundled together. they need to be in twisted pairs to help with shielding hum. Man o man what a nightmare as I really look at everything as a whole. I have also found what appears to be an added wire the tech did that looks to be a ground loop. F'me Maybe I just need to start over on this, toss the PCB and do a hand wired version of it.. LOL Just kidding as that would be a real PITA. mk Quote Link to comment Share on other sites More sharing options...
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