Tested for shorts for the Red wire on the schematics, and it seems it's all good, I get about 75kOhm on C1+, C2+ and onward.
Fashioning a new fuse holder for more standard size fuses, and also thinking of installing the CL-90 current inrush limiter. It could go Red wire from Power primary to the PCB if I'm not mistaken, but will check around the Tubelab website and the forum before installing anything.
Fashioning a new fuse holder for more standard size fuses, and also thinking of installing the CL-90 current inrush limiter. It could go Red wire from Power primary to the PCB if I'm not mistaken, but will check around the Tubelab website and the forum before installing anything.
Ok, saw someone install his CL-140 at the new TR1 points, which are jumpered in mine:
Since the CL-90 is too thick to fit in, I might clip its legs until near the sheath, then solder to the jumper legs protruding, an only after that snip the jumper in the middle on the other side, unless I find another way to wire it in more easily.
Since the CL-90 is too thick to fit in, I might clip its legs until near the sheath, then solder to the jumper legs protruding, an only after that snip the jumper in the middle on the other side, unless I find another way to wire it in more easily.
12AT7 - Pin 2 issue
All right, after rewiring the CL-90 with the new fuse (I put the CL-90 next to the fuse actually), and re-doing one OPT to PCB terminal connection, I performed the amp off check routine as described by Ty.
Everything at amp off checks out ok, except for a single thing:
the smallest tube, 12AT7, pin 2 is giving me only 1.2kOhm instead of 220kOhm...
Could C10 have gone to oblivion?
All right, after rewiring the CL-90 with the new fuse (I put the CL-90 next to the fuse actually), and re-doing one OPT to PCB terminal connection, I performed the amp off check routine as described by Ty.
Everything at amp off checks out ok, except for a single thing:
the smallest tube, 12AT7, pin 2 is giving me only 1.2kOhm instead of 220kOhm...
Could C10 have gone to oblivion?
For the 12AT7 pin2, the datasheet gives #2 grid, so that means on the schematics I should get 221kOhms from ground to pin 2 - R11 (220k) + R12 (100 ohm), but now I get varying values, like 5K, to 8K...
I already lifted R11 and verified it and soldered it back in.
I guess I'll need to verify R12 lifted and also re-solder that noval socket.
Other than that, I am at a loss to troubleshoot this.
I already lifted R11 and verified it and soldered it back in.
I guess I'll need to verify R12 lifted and also re-solder that noval socket.
Other than that, I am at a loss to troubleshoot this.
My right channel won't play: there's just slight buzzing on the loudspeaker. Could it be that one half of the 12AT7 is dead? What could I do to diagnose this channel completely?
Had to do a fair amount of work today because the RCA inputs salvaged had a weird short between one side's signal and ground terminals. Repaired that and tested thoroughly, and also found out the cables I was using for the inputs was not good enough: at the very slight twist, the shield/ground would break. So I ended up making two new input cables with CAT 5 braided cables and re-tested. Re-wired the OPT as not inverted for checking CFB.
At that point, the connections were tested for shorts and continuity and all was fine.
Did the amp off check and all tested ok. Did the amp on check and all tested ok.
On powering up the amp, there was a building screech, most probably oscillation, so I had to rewire the OPT as inverted for CFB this time.
On powering up this time around, no screeching, but the usual hum that I had before, so I think inverted for CFB is good for the Edcor CXSE OPT but Right channel doesn't work.
Powered down, noticed the KT-88 were quite hot, so had to wait quite a while, maybe 1 minute or two, then swapped them and powered on again.
Here again, no right channel. so if a tube is the culprit, I believe it could be the 12AT7 which connects to both power tubes, but at this point, it coud be anything in the path, couldn't it?
Frustrating to hear only one channel after all this work today... But the glimpse of the one channel is, of course, promising.
Had to do a fair amount of work today because the RCA inputs salvaged had a weird short between one side's signal and ground terminals. Repaired that and tested thoroughly, and also found out the cables I was using for the inputs was not good enough: at the very slight twist, the shield/ground would break. So I ended up making two new input cables with CAT 5 braided cables and re-tested. Re-wired the OPT as not inverted for checking CFB.
At that point, the connections were tested for shorts and continuity and all was fine.
Did the amp off check and all tested ok. Did the amp on check and all tested ok.
On powering up the amp, there was a building screech, most probably oscillation, so I had to rewire the OPT as inverted for CFB this time.
On powering up this time around, no screeching, but the usual hum that I had before, so I think inverted for CFB is good for the Edcor CXSE OPT but Right channel doesn't work.
Powered down, noticed the KT-88 were quite hot, so had to wait quite a while, maybe 1 minute or two, then swapped them and powered on again.
Here again, no right channel. so if a tube is the culprit, I believe it could be the 12AT7 which connects to both power tubes, but at this point, it coud be anything in the path, couldn't it?
Frustrating to hear only one channel after all this work today... But the glimpse of the one channel is, of course, promising.
Troubleshooting single channel issue.
Yesterday, I did some troubleshooting routine following the instructions in a post by George, connected the C11 & C21 'left' legs and powered on, putting the amp in a configuration where either driver circuit feeds the outputs.
The amp then does output on both channels, albeit with lacking some bass/mid-range.
Based on George's instructions, it seems I have an issue with the input circuits.
I am tempted to replace both the CCS and the 12AT7 tube.
Here are George's instructions in the 'Left channel dead' thread:
Yesterday, I did some troubleshooting routine following the instructions in a post by George, connected the C11 & C21 'left' legs and powered on, putting the amp in a configuration where either driver circuit feeds the outputs.
The amp then does output on both channels, albeit with lacking some bass/mid-range.
Based on George's instructions, it seems I have an issue with the input circuits.
I am tempted to replace both the CCS and the 12AT7 tube.
Here are George's instructions in the 'Left channel dead' thread:
More Troubleshooting and grounding question...
I rewired the amp in Triode mode as there are less connections to diagnose, but still no go for the right channel.
Before I connected the amp, I checked the + speaker terminals and they appear to be connected to ground somehow.
This shouldn't happen, right? The only ground on the speaker terminals in the triode configuration should be the -ve ones, isn't it?
I rewired the amp in Triode mode as there are less connections to diagnose, but still no go for the right channel.
Before I connected the amp, I checked the + speaker terminals and they appear to be connected to ground somehow.
This shouldn't happen, right? The only ground on the speaker terminals in the triode configuration should be the -ve ones, isn't it?
Received a new transistor that I swapped for the one in the right channel.
This time, the right channel does some 'flaring' sound, like 'flsrsshwwwp', lots of low frequency content, suggesting the previous transistor had blown, and that I still probably need to test in a new 12AT7 tube.
In the meanwhile, one ordered from tubedepot is taking some time to reach me, but at least my DAC has been repaired.
I have been reading about snubber circuits to damp the power supply resonance, something like either an RC or C || RC across the power transformer secondary.
The electronic plan so far is the following (I have removed the microprocessor integration from the To Do list):
1. Repair the channel by trying a 12AT7 swap, and failing that, do more extensive diagnosis for the channel (how?).
2. Test UL + CFB mode once it is working completely
3. Add a snubber circuit across power transformer secondary for damping
4. Consider adding choke
5. Consider adding supplemental capacitor
This time, the right channel does some 'flaring' sound, like 'flsrsshwwwp', lots of low frequency content, suggesting the previous transistor had blown, and that I still probably need to test in a new 12AT7 tube.
In the meanwhile, one ordered from tubedepot is taking some time to reach me, but at least my DAC has been repaired.
I have been reading about snubber circuits to damp the power supply resonance, something like either an RC or C || RC across the power transformer secondary.
The electronic plan so far is the following (I have removed the microprocessor integration from the To Do list):
1. Repair the channel by trying a 12AT7 swap, and failing that, do more extensive diagnosis for the channel (how?).
2. Test UL + CFB mode once it is working completely
3. Add a snubber circuit across power transformer secondary for damping
4. Consider adding choke
5. Consider adding supplemental capacitor
Received the new 12AT7 from tubedepot, took ages to reach here.
Swapped it in, but still no luck with the right channel so the plan is to troubleshoot that whole right channel step-by-step.
I'll start with checking for shorts at the input then follow along the schematics and components.
If anybody has good information on how to do this, I'm all ears.
Swapped it in, but still no luck with the right channel so the plan is to troubleshoot that whole right channel step-by-step.
I'll start with checking for shorts at the input then follow along the schematics and components.
If anybody has good information on how to do this, I'm all ears.
My work area
Since I am always managing to make a mess in the dining room, in full view of any vistior/friend even after supposedly cleaning up, I was forced to set up a small new laboratory-slash-workshop area.
It's next to my synths and in the same room as the audio/video equipment, so DIY with music is possible, and it's familiar territory.
Note the cunningly placed brown curtain, which handily hides all the salvage box underneath the table, although we're not immune to a cable peeking out.
On the table today is my DIY SET Tube Amp. I shudder at the thought of working on it every time: it's heavy. However, the Edcor transformers also make convenient 'feet' while I am diagnosing and working on the circuit.
The old Windows laptop, whose USB board doesn't work anymore is used solely as a way to access documentation on the net while troubleshooting, designing and researching or posting on audio forums, as well as for doing some LTSpice simulations.
Since I am always managing to make a mess in the dining room, in full view of any vistior/friend even after supposedly cleaning up, I was forced to set up a small new laboratory-slash-workshop area.
It's next to my synths and in the same room as the audio/video equipment, so DIY with music is possible, and it's familiar territory.
Note the cunningly placed brown curtain, which handily hides all the salvage box underneath the table, although we're not immune to a cable peeking out.
On the table today is my DIY SET Tube Amp. I shudder at the thought of working on it every time: it's heavy. However, the Edcor transformers also make convenient 'feet' while I am diagnosing and working on the circuit.
The old Windows laptop, whose USB board doesn't work anymore is used solely as a way to access documentation on the net while troubleshooting, designing and researching or posting on audio forums, as well as for doing some LTSpice simulations.
One suggestion I have is to do resistance readings at all points between the 2 channels and compare. I had one dead channel on startup and found my problem this way. If at the same point of the audio chain you have a different reading between the good side and the bad side you have a section to start looking in. Diagnosing is first determining which section the problem is in then you can narrow it down to a few components. It is best to have the right test equipment but when you don't finding the problem can still be done but it is much easier when you narrow down the problem to fewer components.
The schematic luckily is elegantly simple.
Swap everything between L and R that you can even if you think you ruled something out.
What is your input source? Functioning properly?
Swap cables
Swap opts
Swap coupling caps
Double check all grid stoppers in suspect channel
Make sure input rcas are not shorted to ground
12at7 and the ccs are pretty robust which leads me to something simpler.
Swap everything between L and R that you can even if you think you ruled something out.
What is your input source? Functioning properly?
Swap cables
Swap opts
Swap coupling caps
Double check all grid stoppers in suspect channel
Make sure input rcas are not shorted to ground
12at7 and the ccs are pretty robust which leads me to something simpler.
Hey wdecho, thanks for the suggestion, great idea indeed.
Yesterday, I re-wired in simple Triode mode, this took me a long time, but at least I can probably diagnose easier with it.
Today, I measured the resistors on the right channel, they seem to all check out good.
Indeed, and that's a good thing from tube amp designs. However, it's hard to know where to start with this kind of issue.
Thanks for the suggestion, it could be cool to swap the coupling caps I think, and perhaps other caps. When I diagnosed using George's method, both outputs work, so I think the OPTs are still OK, and the issue is narrowed down to the input section.
Good to know, and a bit surprising for the CCS - I thought that since it was an IC, it could easily be damaged.
Swapping 12AT7 gave nothing different, so I think my tube is OK.
I also did a quick check for shorts with the inputs, and they're OK.
When you take a reading say at the grid of the 12AT7 good channel compare it with the reading on the non working channel 12AT7 grid and see if they match and so on and so forth and see if every point on both channels are the same. When you run across the point that has a different reading than the good channel you have made progress.
Then you can do the same thing with voltage readings both DC and AC and compare. You have one channel you know is good so compare impedance and voltage readings between each channel. You are going to find something, voltage or resistance, that is not the same as the good channel. Then you will have localized the trouble then start looking at those components in that part of the circuit.
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Double check values for r10 13 14 and 19
What is each section running in mA? Measure above and below the triode section across the resistor once you confirm the values are correct. This will at least tell you if the ccs is functioning and that it's a signal issue instead. Separate between pure tube function vs how the signal travels.
Again double check grid stoppers that they aren't mis valued...
Lastly don't count on the label the resistors came in were correct...measure measure measure...
What is each section running in mA? Measure above and below the triode section across the resistor once you confirm the values are correct. This will at least tell you if the ccs is functioning and that it's a signal issue instead. Separate between pure tube function vs how the signal travels.
Again double check grid stoppers that they aren't mis valued...
Lastly don't count on the label the resistors came in were correct...measure measure measure...