So I picked one up today and nearly pulled my back out at a garage sale. Owner said its blowing fuses. So I brought home, pulled all the tubes, put in a fresh fuse, turned it on and yep! It blows fuses hard and fast. So next, I opened it all up and all the caps test good (using a BK cap tester) and without the tubes installed, I power the SE100 again; this time with a variac and found it pops fuses right at about 30 volts. So next, I isolated the PSU and let it run for a couple minutes at 25 volts while I monitor all the PSU components with a infrared thermal gauge,. Everything stayed cool but the choke, which got too hot to touch in less than 2 minutes. I'm guessing it shouldn't do that, but I don't know. So next I unplugged the choke, and powered the ampup again. Now its stoped blowing fuses. But without schematics or values, I have no idea if any of my findings means anything. The choke has part numbers on it. 15-HL-151-10-15 and B100CHK01113. Does anyone know what the numbers mean? I'm guessing its a 15 henry with maybe a 5 amp capacity just from the size. But it benches at 2H with internal resistance of 28 ohms. Again, that doesn't sound right, but I have no way of knowing. Does anyone out there know where I might locate some schematics or a parts list or know anything about these amps or the choke? I don't think I've ever seen one this big! Kinda the common theme for this whole amp. BIG! Thanks everyone. Jim
My guess is that you have found the problem. Verify by ohm-ing it!
As for choke ( it's for B+ ?) you can use just about anything that has the right current capacity, at least for testing.
As for choke ( it's for B+ ?) you can use just about anything that has the right current capacity, at least for testing.
Has the chokes insulation broken down? Can you not repair it as it uses E I lamminations and an air core? Easy to take to bits and rewind.
It won't be 5A, more like 500mA.
I agree on the assumption of 15H.
It won't be 5A, more like 500mA.
I agree on the assumption of 15H.
When you "unplugged" the choke, does that mean that you disconnected it, and not re-connected anything? If so, you also disconnected everything downstream from it, including a lot of stuff. Don't buy a new choke yet - you're not done trouble-shooting.
All good fortune,
Chris
All good fortune,
Chris
Thanks petertub, JonSnell and Chris Hornbeck. Jon, The choke looks brand new. I don't think this is an air core. It looks like a conventional power transformer...just with two leads. No signs of "well done." And you're right about the current draw, aside my my poor late night humor, 500ma is probably closer to correct assuming 10x50ma. At least for testing if I can find something cheap to experiment with until I can learn more. If it turns out to be the problem, I'd like to replace with a factory unit if at all possible. Meanwhile, I'm still looking for schematics or someone with an SE100 willing to put a meter on theirs and see what they get. Or.....someone parting out an SE100 willing to sell the choke. Chris.....you're right of course about additional down-stream issues but without schematics or any knowledge of these Golden Tubs Amps what-so-ever, I first did a detailed visual, tested all the E-caps and then simply started the line cord and started testing parts until I found a problem and, where I don't know of an absolute test or dry dock specifications for this choke, the fact that with only 30 volts on it from the variac, it heated up to over 300 degrees in only two minutes (using an infrared thermal gauge), suggested that this might be a good place to start. I'd thought about testing the amp by simply shorting past the choke and bring the power up again with the variac, but I'm not confident enough in my ancient electronics to know if that would be a good idea, so my next step is to see if I can find a used or surplus choke spec'd close to what we think this one should be. I'll be shooting for 10-15H, 500-600ma. I continue to be totally open to anyone's input, suggestions, ideas, questions or advice. Thanks to everyone! Jim
To those with more engineering than I have, would this work?: Theory: for the choke to be causing fuses to blow, it would have to short against its own windings or to ground and would need enough signal voltage for the V to "jump." To check if the choke is actually bad and not reacting to some other problem downstream, could I replace the choke with a hefty resistor rated the same as the static resistance of the choke (28 ohms) and see if the amp starts blowing fuses again? If it does, I would know to keep looking downstream for the culprit, but if it quits blowing fuses, I would know to keep looking for a similar choke for at least testing. Maybe anything over 1H 500ma 25 volts for testing. Any thoughts?
HAH! This is the first time I've heard that phrase since about 1968 when I built one in my Electronics 1 class in high school to test our first builds.....a 5 tube AM radio.
Disconnect only the downstream side of the choke, and retest. Now the choke and its insulation is still in play. The choke is likely the victim, not the perpetrator. And, a lamp limiter is handy, even if you have a variac, for finding intermittent kabooms.
All good fortune,
Chris
All good fortune,
Chris
This amp is quite unconventional. The first EL34 (V2) drives a phase splitting interstage transformer. The next four EL34s are output tubes and their cathodes seem to sit at -550V with the plates grounded via a resistor, probably for current adjustment measurements. It’s operating as a push-pull-parallel cathode follower. I imagine that output transformer has pretty low ratio since the cathode to cathode side should be fairly low impedance. I got this from a cryptic schematic posted on audiokarma (which I have not carefully studied), but might be useful to you.
Has anyone seen this circuit..Its a golden tube se100 and | Audiokarma Home Audio Stereo Discussion Forums
Before going any further I would try to identify any damaged or burned resistors if you are sure all caps are good in the power supplies. Be careful to observe polarities of the caps in the unusual high voltage B- supply at -550Vdc. Unfortunately no power supply schematic that I could find.
Then try to test the tubes to see if they are good. Next, testing the power supply with a 30-50 ohm resistor in stead of the choke (first without tubes, and if all well with tubes, adjusting the bias on each output tube - don’t know what the current should be, but 30 ma should be a good starting point, given the 550 Volts across the tubes). Be sure to put a load on the output transformers when testing with tubes in. The amp will probably hum without the choke, but should play and not blow fuses if the circuit is all good, meaning the choke is the culprit.
This will be the time to get a new choke. Based only on a photo I have seen of the size of the choke, my guess would be 3-5 Henry, 500-600 ma choke, but I could be way out.
Good luck.
Last edited:
Progress has been made. I completely disassembled it and first went through the power supply. One cap was disconnected via a cold solder joint. Fixed. All the caps tested on the + side of their ratings via a B/K cap tester. All the resisters tested right on. I'm guessing it had been dropped or worked on somewhere along the way because all the leads coming out of the power transformer had become separated from the little bushings and some appeared to maybe short against the shell, so I removed the whole assembly, realigned all the leads with their bushings, anchored everything down with dabs of urethane sealer and reinstalled. Then reinstalled the PSU boards and tested. Full power and no blown fuses. Next, reinstalled the main PCB with tubes removed and all bias zeroed. No blown fuses, but one of the bias pots will need to be replaced. Its currently on its way from Mouser. SAme with a couple of the 11 ohm resistors. One had smoked and was replaced with a pair in series and another had discolored the board and looked on its last leg so I'm just going to replace all the 11 ohm with precision resistors, so they're on their way from Mouser, too. All the caps (especially the tiny decouplers which I've read have a history of shorting out on these amps) tested right on them money. Power up.....no blown fuses. Power down and install the tubes. Power up.....no issues. Next, reinstall the finally assemblies including those 15 pound output transformers. Connected everything up and power.....pow! blown fuse. Isolated one of the output transformers and unistalled it. Blown fuses stopped. Reversed the two output transformers and the problem followed the suspected iron. Double checked myself by reversing their places, running just one in both channels and then the other.....and in all cases, the problem followed the same transformer. And last, simple DC resistance tests and the two transformers test totally different though none of the results make any sense to me. I'm guessing there are at least t2 shorts in the windings....And last, I pealed all the wrappers off the suspect transformer to see if I could see anything simple. It appears that some of the lacquer had melted and baked on one side but nothing burned or burned smelling. All the connections to the outside leads appear fine. So as best I can tell, I have a bad output transformer. I've started looking for an OEM replacement....or maybe getting this one fixed or rewound..... So at this point, I could sure use some advice if any of you know of a trustworthy transformer repair/rewind source. Meanwhile... for now, it's taken its place on the shelf (close to the ground as this thing weighs 80 pounds!) with all my other "almost" finished restoration work.