| Posted by Brian | November 04, 2018 - 01:56 am |
| Art, Thank you for the additional information on the transformers, and for all the troubleshooting assistance the past few weeks. Your time spent helping me is very much appreciated! As I mentioned below (and you've no doubt read by now), I'm going to sit back and relax and enjoy the system now that it's up and working. I was able to get the bias dialed in and everything sounds great! I might shift focus to the FM-3 as I know it has capacitor issues, too... but at least I'll have warm music to keep me happy while I work. One day it'll turn cold here in Southern California and I'll be happy staying warm by tube-light. |
| Posted by Brian | November 04, 2018 - 01:51 am |
| Dave, I appreciate that you're keeping the boards available for people like me! Sounds like a wonderful community of folks (you, Art, George, Steve) who are working in parallel to keep the knowledge transfer going. Thank you! For the past week I've been enjoying using my PAS-3 and ST-35. What started as an annoying hum (in the PAS-3) turned in to quite the project, in terms of time and money, but led me to you and Art who helped me on my journey. In the end, for now, I think I'm just going to enjoy the system as it is today. I do plan on ordering the PCBs for future use - I'm afraid if I don't order them now when I go to order them in the future I might find that you have gone the way of George and moved on to other endeavors! But it's been nice to turn it on and listen, and with the Holidays coming I want to be able to turn on Nat Cole and listen through my Dyna like I heard growing up! I don't want it to be in-progress during Christmas this year! Thank you again for your help! |
| Posted by Art Grannell | October 27, 2018 - 08:24 pm |
| Brian, Just a word about your transformer leads. These amplifiers used two different output transformers, that are thought to be electrically identical. The earlier production transformers with the cloth leads were built in the US. Sometime during production, Hafler switched suppliers and used vinyl-leaded transformers manufactured in Japan. The amplifier in this article is a real "odd-ball", with both cloth and vinyl, and I'd only be guessing as to why. I have replaced leads on Z-565's at the core, but only on the secondary (output) side. The core windings are insulated with an impregnated paper of some sort, that shows some "brittleness" due to age. After removing the end bells, and working carefully, I was able to unsolder and remove the secondary wires at the attachment point and replace them. I'd intended to also change the primary leads, but this turned out to be far more difficult as they are attached deeper in the core to the very small wire used in the primary winding. I was uncertain that I could do this without destroying these valuable units, so I opted for a different approach. I cut off the old leads about one to two inches past the exit hole and spliced on new leads using uninsulated butt splices and heat shrink tubing. This is a compromise, but if the wire is otherwise unusable, it will work. These splices cannot be used internally because of lack of space. If you remove the end bells, I suggest that fiber or nylon washers be placed under the screw heads. Some Dynaco transformers had them, some did not, but if the end bells are removed, it's a good idea to use them. |
| Posted by Dave | October 27, 2018 - 07:43 am |
| Hi Brian -- Thanks for the kind words! However, much of the credit belongs to George Ronnenkamp of Audio Regenesis at: http://www.audioregenesis.com/ George was originally selling the beautiful boards I now sell, so credit for their physical design and installation material goes straight to him. He is a wonderful friend and superb Electrical Engineer - as is Steve Lafferty, who owns, operates and maintains the Tronola website here. George approached me several years ago about incorporating my EFB modification into his boards. A rare thing as otherwise, with little exception George's boards remained utterly true to the original Dynaco design and execution. But the EFB™ modification represented a solid performance improvement over the original design that George appreciated. An arrangement was struck, and the new EFB power supply boards became a reality. Later, when George decided to move away from selling the boards, he graciously allowed me to continue selling the boards under the D Gillespie Designs banner. To keep it simple and economical, I decided to sell the boards un-stuffed, whereas George had been selling the boards fully assembled. That required an assembly manual for each board in addition to the installation manuals, which again, George spearheaded. The rest as they say, is history. At any rate, you should check out George's site. He is as much of a Dynaco fanatic as anyone around, and a stickler for remaining true to the original Dynaco brand. Ergo, the manuals are written much as if Dynaco had written them themselves! As to your findings, if the electrical condition of Eyelet #9 was as you say for the left channel amplifier board, then the current draw through V3 would certainly have been quite erratic and unstable -- and changed with any heating or mechanical flexing of the board. Therefore, it's virtually a certainty that you found your problem -- Congratulations! BTW -- If it helps you any regarding the decision to replace your boards, construction of the original boards was never a part of any Dynaco product. They always came fully assembled and ready for installation in the kit. That is one element of the kit then that your dad did not have to build. This is hardly an effort to promote a sale for the new boards, as I understand as much as any the emotional attachment that can be had with things from our childhood that involve our parents. Actually, the old Dynaco boards are the greatest advertisement of all for replacing themselves! The problem you found is common, and will only continue to spread over the boards with time and use. When the time comes, the new boards will return the unit to worry free operation for another 50+ years and beyond -- this because the new boards (and today's components) are so vastly improved over what was originally available at the time. Good luck with your ST-35! Dave |
| Posted by Brian | October 26, 2018 - 05:42 pm |
| Dave, First, I wanted to compliment you on the thoroughness of your instructions. You took the time to create a very detailed and complete technical documentation package and at every point of troubleshooting when I thought to myself, "I wish I had this information," I referenced your instructions and the answer was there. The red-line schematics were especially helpful. Second, I want to thank both you and Art for sharing your knowledge with me. I would not have been able to do this on my own. As a result of your recommendation I took a hard look at the underside. Though there are several loose terminals in the sockets, they seemed to be pretty evenly and randomly located throughout the sockets, so I looked elsewhere first. I noticed what looked to be a slight lifting of the eyelet #9 ring from the board. I had previously noted a slight convex bend in the board (when viewed from above). I took some resistance measurements from the eyelet to adjoining components (R9 and C5) found it changing from open to short as I pressed on the eyelet, causing the board to flex at the same time. As a test-fix I carefully soldered a wire to the three points, effectively bypassing the eyelet and the traces. It's preliminary, but so far the cathode voltage appears to be stable. I haven't declared victory yet - the tube socket could still have an impact - but it feels good to have a glimpse at success. That said, I have to make a decision on how to proceed. I'm not crazy about my point-to-point solution as a fix. Art had previously suggested I take this time to replace the PC-13 boards entirely, which would be prudent given the problems discovered based on the age of the boards. My cause for pause is twofold: 1) Personal: I have photos of my dad building the Dyna Kit in 1963, and if I replace the PC-13s entirely there isn’t much left of the original work! The instruction books even match the serial number of each unit (PAS-3, ST-35, FM-3). 2) Technical: The cloth-covered wire coming out of the transformers is in varying states of quality. The power transformer leads seems to be OK, however the leads that connect to the output tubes is in various states of crumbling. I had to be careful moving the wire from pin 9 to 8 as part of the EFB modification. One of the leads required some shrink tubing to avoid having any more cloth flake off while handling with the needle nose. I think I could get away with splicing for all but one pair, which is in bad condition going through the through-hole into the transformer itself. I’m guessing to do the repair properly I’d have to send the two output transformers to someplace to have them taken apart and new leads put on? Anyway, at least I’m entering the weekend with some success on the amp. I can’t thank you and Art enough for your time and knowledge sharing. Once I make peace with the fact that I need to replace the PC-13s you’ll see my order! |
| Posted by Dave | October 24, 2018 - 12:59 pm |
| Hi Brian -- Steve asked me to look in on your conversation here since there was a comment made about an error in the instruction manual for the ST-35 EFB™ Power Supply Board. There is, and thank-you for spotting it! For the record, the schematic for the board itself is correct, with the overall schematic containing the error. Again, my thanks for spotting it. If I may comment on the issue you're having however, it would seem to boil down to just a few possibilities. You've already eliminated the coupling cap possibility by replacing them. And, you've eliminated the tube possibility by trying the tube in the other channel, with the problem always remaining WITH THE ONE SOCKET. This is important, and can only be verified by the fact that ANY tube placed into the identified socket will intermittently red-plate -- the point being that no tube installed into its mates socket (i.e. same channel) will show such offending behavior. So running with that assumption then, the only possibilities that will cause the problem you're having based on the symptoms given include: 1. The 1000Ω; resistor attached to pin 2 of the offending socket is defective, or it's associated 470K grid return resistor is defective. Given your examinations, these possibilities are remote, but none the less would cause the problem you're having. 2. Pin #2 within the offending socket is internally broken, so that sometimes the connection is made, sometimes not. With older equipment that has gone through many heat stress cycles, this can happen -- and does, as I've personally witnessed. If this is the cause, usually the bottom side terminal can be simply pulled out of the socket, where normally it cannot be. 3. By far however, the greatest possibility is that a circuit board connection or trace that looks good, is in fact, not. The old Dynaco phenolic boards are famous for developing a complete circular break in the solder connection where leads and terminals of the board components extend through the hole in the board - and/or developing breaks in circuit traces. These are usually quite small and most often cannot be seen with the naked eye, requiring close inspection, ideally with a magnifying glass to spot. It can be either at a component lead, terminal connection, in the middle of a trace, or at one of the eyelets. In this case, a prime target is any board connection or trace involving the path that pin 2 of the offending socket takes in reaching ground through its associated 1KΩ; or 470KΩ; resistors. Remember too that there can be multiple breaks in the path. The bottom line here is, that if the tube and associated coupling cap for the offending socket have been positively eliminated, and the problem only occurs in the one socket regardless of tube installed, then the problem can only be either the actual terminal for pin 2 in the offending socket, or the connections/components that ultimately allow pin 2 of that socket to reference ground as discussed. This is one of those cases where if the facts are true, then the problem will be found in the areas mentioned. If the problem is not in the areas mentioned, then the symptoms taken as fact are in question. Good luck with your search -- I hope this helps! Dave |