Yes. Exactly as shown in your photos #4 and #5.
TR1 looks as it did when new, and measures 63 ohms (on the board).
5V center tap is cut blunt, shrink-tubed and coiled up.
I am confused why you suspect a 5V issue. I thought we verified 5V is working in the first test (heaters worked for both the rectifier and power tube).
I just noticed something that might be another clue.
C3 has a bulge in one side and there appears to be some sooty residue on the board very close to where it sits. I am assuming it is toast by looking at it. I never noticed this before so I don't know if it happened during the initial event, or during subsequent testing.
Not sure if this helps us narrow down the problem, but I am going to remove it for now since it very likely needs to be replaced.
C3 has a bulge in one side and there appears to be some sooty residue on the board very close to where it sits. I am assuming it is toast by looking at it. I never noticed this before so I don't know if it happened during the initial event, or during subsequent testing.
Not sure if this helps us narrow down the problem, but I am going to remove it for now since it very likely needs to be replaced.
If you look at the SSE schematic, you see that when the rectifier tube is installed, the high B+ voltage is taken from the cathode of that tube. This means that when the rectifier tube is installed, and the high voltage secondary is connected to the board, all of the B+ voltage appears on the 5V winding of the transformer. If this insulation breaks down, the high voltage will short / leak to somewhere, usually ground. This is possible, but very, very, unlikely.
If you have not removed / disabled the rectifier diodes, they should be disabled. They are known to have caused this problem in a small minority of builds. You can do this by cutting one lead of each diode to remove it from the circuit. Also, at this point, in lieu of trusting resistance and capacitance measurements, I would unsolder and lift from the board one leg of the filter cap C1 and the bleeder resistor R2, to remove them from the circuit and repeat the test. If the voltage comes up and stays, one of these components or the diodes is bad.
There really is nothing else to go wrong before the choke, unless there is a foreign contaminant on the board creating a high voltage path to ground.
If you have not removed / disabled the rectifier diodes, they should be disabled. They are known to have caused this problem in a small minority of builds. You can do this by cutting one lead of each diode to remove it from the circuit. Also, at this point, in lieu of trusting resistance and capacitance measurements, I would unsolder and lift from the board one leg of the filter cap C1 and the bleeder resistor R2, to remove them from the circuit and repeat the test. If the voltage comes up and stays, one of these components or the diodes is bad.
There really is nothing else to go wrong before the choke, unless there is a foreign contaminant on the board creating a high voltage path to ground.
I do appreciate the attempt to help me, but I this makes my brain hurt. The B+ ends up on the 5V winding? I don't even know how to begin to understand why this is the case.
I cut the diodes (D1, D2) off the board quite far back in the thread.
C1 has already been completely removed from the board. I'll try lifting one leg of R2 off the board and see what happens.
High voltage AC goes into the plates of the rectifier tube, and high voltage DC (the B+) comes out of it's cathode. That's how a rectifier works. That cathode needs to be heated, so it gets it's own 5 volt heater winding. If the 5 volt winding was connected to ground, the insulation that seperates the heater from the cathode would need to handle about 500 volts while being heated to nearly 600 degrees. It's simpler (especially in the 1950's when these tubes were invented) to simply connect the heater and cathode together and use a seperate heater winding inside the transformer with good insulation.
The blown C3 leads me to think in a different direction.....somehow B+ got into the 6.3 volt winding since C3 goes from the 6.3 volt heater winding to ground.
Take your ohmmeter and measure the resistance between the green transformer wires and the yellow transformer wires. There should be no connection. I looked back through every picture in this thread and they do appear to be separate inside the chassis.
In normal service that cap has about 40 volts on it. That all comes through R4 which should be a 150K resistor. I looked back at all of the pictures, and it does indeed look like a 150K resistor, but I would measure it, or lift one end and repeat the dim bulb test.
All combinations of green-to-yellow measured infinite resistance.
R4 measurement = 155K ohm
You know, ...
It might seem like a lot more work at first, but - and, I'm just saying this, if it was me, I would take a couple of hours and remove/disassemble every single component and part. I'd measure every resistor and capacitor and replace anything suspect. I'd check the continuity of every screw terminal as well as every tube socket and its corresponding eyelet tab, etc. I'd examine the board for any accidental solder bridges or damaged traces.
Then, I would approach it as a brand new project. I'd build it from scratch all over. And, most importantly, I'd build it 100% stock with no added features. [They can always be added later after it's working.]
Somewhere, in your original build something was either defective, or connected wrong. The design works when everything is correct and all of the components are functioning.
It might seem like a lot more work at first, but - and, I'm just saying this, if it was me, I would take a couple of hours and remove/disassemble every single component and part. I'd measure every resistor and capacitor and replace anything suspect. I'd check the continuity of every screw terminal as well as every tube socket and its corresponding eyelet tab, etc. I'd examine the board for any accidental solder bridges or damaged traces.
Then, I would approach it as a brand new project. I'd build it from scratch all over. And, most importantly, I'd build it 100% stock with no added features. [They can always be added later after it's working.]
Somewhere, in your original build something was either defective, or connected wrong. The design works when everything is correct and all of the components are functioning.
I appreciate your input, however I think you missed one important detail; this amp worked perfectly for over 8 hours when I first built it.
Then I rewired for UL mode and fired it back up. It worked for 2 more hours and then made a bad noise and produced smoke.
Also, the board is 100% stock. I talked a lot about mods early in the thread but I did not implement any of them yet.
I am now 100% positive that the smoke came from the fried C3 that I discovered eventually. Why it fried is still a mystery.
Then I rewired for UL mode and fired it back up. It worked for 2 more hours and then made a bad noise and produced smoke.
Also, the board is 100% stock. I talked a lot about mods early in the thread but I did not implement any of them yet.
I am now 100% positive that the smoke came from the fried C3 that I discovered eventually. Why it fried is still a mystery.
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This thought has occurred to me. 
However there are a few things holding me back.
1) I don't know why C3 fried in the first place.
2) I'll need to place an order through Mouser, and pay $20 shipping on a ~$1 cap - I'd like to figure out #1 above before spending any more money.
3) The other tests George had me run have failed, so it doesn't seem to me like replacing C3 is going to fix anything.
4) Depending on what the actual problem is, I may need other parts and I would rather order all needed parts at the same time (see #2).
5) If I don't address the root cause, then my very expensive (see #2) capacitor will simply burn up again.
However there are a few things holding me back.
1) I don't know why C3 fried in the first place.
2) I'll need to place an order through Mouser, and pay $20 shipping on a ~$1 cap - I'd like to figure out #1 above before spending any more money.
3) The other tests George had me run have failed, so it doesn't seem to me like replacing C3 is going to fix anything.
4) Depending on what the actual problem is, I may need other parts and I would rather order all needed parts at the same time (see #2).
5) If I don't address the root cause, then my very expensive (see #2) capacitor will simply burn up again.
Still having internet connectivity issues. The broken pole that was hanging in the trees in June (post #173) is still hanging by the wires in a tree. When the wind blows, the modem resets and takes 3 to 5 minutes to reconnect.
I'm still trying to figure out what is wrong here and how to fix it. Given the new information that C3 was the smoke source, I have reread the entire thread again and carefully studied all the pictures, intermittently over a few days.
We know that C3 fried. To get a capacitor like this to split open and smoke requires more voltage than the cap was rated for, and once the excess voltage causes the cap to fail, some serious current is needed to make it smoke. So we know that a lot of voltage AND a lot of current went through C3.
In normal use all the voltage applied to C3 comes through R4. There is no way that enough current to smoke a cap could come through R4 unless it was a wrong value (way to low), and if it was, R4 would be fried too. R4 is the correct part, and has been confirmed to be OK (measures correct in post #187).
There is a good possibility that the condition that blew C3 is still present, and this should be investigated before making any more smoke, or possible dead parts. Fortunately we can do this without C3. In fact the amp will work without C3, but may have more hum than with it in place.
What we have to figure out is how did excessive voltage get there, and is it still present. The clues so far point to a B+ problem, dim bulb tests with the rectifier tube in place fail, but those without it pass. No rectifier, no B+.
Before chasing that rabbit down it's hole, lets explore something I saw back in the early posts. In post #41 you switched primary taps from the 125 volt tap to the 115 volt tap to get more B+. This was a few days before switching to the UL tap (post#47).
The picture in post #69 (one day after smoke) shows the black wire from the power transformer (primary tap) and the green-yellow wire (6.3 volt CT) leading into the same blob of tape. If these two wires were to become connected to each other, it could put AC line voltage on the 6.3 volt heater circuit, and DIRECTLY ON C3, with enough current to make smoke.
Before disturbing these wires take your meter, set it on ohms, and with no power connected to the board, measure the resistance between the white transformer wire connected to the AC power receptacle, and either of the green wires connecting to the filament terminals on the rear edge of the PC board. If this resistance on not infinity, or several megohms, you have a problem that needs fixing.
I'm still trying to figure out what is wrong here and how to fix it. Given the new information that C3 was the smoke source, I have reread the entire thread again and carefully studied all the pictures, intermittently over a few days.
We know that C3 fried. To get a capacitor like this to split open and smoke requires more voltage than the cap was rated for, and once the excess voltage causes the cap to fail, some serious current is needed to make it smoke. So we know that a lot of voltage AND a lot of current went through C3.
In normal use all the voltage applied to C3 comes through R4. There is no way that enough current to smoke a cap could come through R4 unless it was a wrong value (way to low), and if it was, R4 would be fried too. R4 is the correct part, and has been confirmed to be OK (measures correct in post #187).
There is a good possibility that the condition that blew C3 is still present, and this should be investigated before making any more smoke, or possible dead parts. Fortunately we can do this without C3. In fact the amp will work without C3, but may have more hum than with it in place.
What we have to figure out is how did excessive voltage get there, and is it still present. The clues so far point to a B+ problem, dim bulb tests with the rectifier tube in place fail, but those without it pass. No rectifier, no B+.
Before chasing that rabbit down it's hole, lets explore something I saw back in the early posts. In post #41 you switched primary taps from the 125 volt tap to the 115 volt tap to get more B+. This was a few days before switching to the UL tap (post#47).
The picture in post #69 (one day after smoke) shows the black wire from the power transformer (primary tap) and the green-yellow wire (6.3 volt CT) leading into the same blob of tape. If these two wires were to become connected to each other, it could put AC line voltage on the 6.3 volt heater circuit, and DIRECTLY ON C3, with enough current to make smoke.
Before disturbing these wires take your meter, set it on ohms, and with no power connected to the board, measure the resistance between the white transformer wire connected to the AC power receptacle, and either of the green wires connecting to the filament terminals on the rear edge of the PC board. If this resistance on not infinity, or several megohms, you have a problem that needs fixing.
Hey cogitech, glad to see you're still willing to suss this out. I've remained silent on the issue so as not to add to the "noise", but I'll also admit it's also because I have a lot to learn here (and I'm certainly not going to argue with the circuit designer! ). Hate I can't do more than be a "cheerleader", but I think the conservative approach you've taken thus far will pay off handsomely.
Keeping my fingers crossed...
). Hate I can't do more than be a "cheerleader", but I think the conservative approach you've taken thus far will pay off handsomely. Keeping my fingers crossed...
I have finally had the time and inclination to revisit this amp.
George, I performed the test you described in the last part of post #193, and the resistance is infinite.
I decided to install a new C3, and re-install C1 (which I had removed to test it). I have the board re-installed back in the chassis and all wired up - basic triode connected with no feedback, choke connected.
Also, I reverted back to the 125v tap on the primary.
I am very tempted to jam tubes in it and fire it up, however I am aware that "fire it up" might be just what happens.
If the problem that fried C3 remains unchanged, then it seems the worst that could happen is C3 fries again. I have 9 more replacements, so ...
I am wondering if maybe my original C3 wasn't the part I thought it was. I am pretty sure this was a part I scavenged from my parts bin. It is a little red WIMA MKS 4 with " 0,47/100- " on it.
I know I have been very cautious up until this point and I have been very interested in trying to discover the problem. At this point I am feeling a little less risk averse and just want the damned thing to work. Maybe I accidentally "fixed" whatever was wrong. That is unlikely, but I have had it happen to me before.
If this is a terrible idea (just fire it up), then please provide some alternative guidance. I almost feel like this deserves a whole new thread. Start from scratch with the troubleshooting.... ?
George, I performed the test you described in the last part of post #193, and the resistance is infinite.
I decided to install a new C3, and re-install C1 (which I had removed to test it). I have the board re-installed back in the chassis and all wired up - basic triode connected with no feedback, choke connected.
Also, I reverted back to the 125v tap on the primary.
I am very tempted to jam tubes in it and fire it up, however I am aware that "fire it up" might be just what happens.
If the problem that fried C3 remains unchanged, then it seems the worst that could happen is C3 fries again. I have 9 more replacements, so ...
I am wondering if maybe my original C3 wasn't the part I thought it was. I am pretty sure this was a part I scavenged from my parts bin. It is a little red WIMA MKS 4 with " 0,47/100- " on it.
I know I have been very cautious up until this point and I have been very interested in trying to discover the problem. At this point I am feeling a little less risk averse and just want the damned thing to work. Maybe I accidentally "fixed" whatever was wrong. That is unlikely, but I have had it happen to me before.
If this is a terrible idea (just fire it up), then please provide some alternative guidance. I almost feel like this deserves a whole new thread. Start from scratch with the troubleshooting.... ?
I got impatient.
Stuck the rectifier in and powered it up via the dim bulb tester, with the multimeter connected to B+ and ground.
Everything appeared to be going well. A very slow climb up to 420-something VDC B+ and very little bulb glow. A bit of that "hot electronics smell, but no smoke.
Then everything went nuts like before, the bulb lit up very brightly and I scrambled to hit the kill switch on the power bar.
A couple minutes after I shut it down, I went and got my infrared thermometer. I was curious. C3 was 45 celcius. I am guessing it was considerably hotter during the test. I am also guessing it isn't supposed to get hot at all.
Stuck the rectifier in and powered it up via the dim bulb tester, with the multimeter connected to B+ and ground.
Everything appeared to be going well. A very slow climb up to 420-something VDC B+ and very little bulb glow. A bit of that "hot electronics smell, but no smoke.
Then everything went nuts like before, the bulb lit up very brightly and I scrambled to hit the kill switch on the power bar.
A couple minutes after I shut it down, I went and got my infrared thermometer. I was curious. C3 was 45 celcius. I am guessing it was considerably hotter during the test. I am also guessing it isn't supposed to get hot at all.
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While I am sure you are frustrated and exasperated, at some point with help from this board, you will find the answer, and it may make you do a Homer Simpson "Doh!" Such is the world of DIY. Sometimes learning is painful, but when you get this baby back to running perfectly your statisfaction and knowledge will both be greater. Kind of like when you can't find your keys and have looked everywhere. Keep the faith. You are close. Don't give up now.
I just re-ran this test and it measures 212 ohms (and the reading only takes a couple of seconds).
Something is seriously wrong here.
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