OK. After chickening out for a few months I decided to tear into this. Here's where I'm at:
*I found one bad capacitor. It's a tiny guy placed between two white resistors near the input transformer.
* the rest of the capacitors are ok according to my ESR meter
*I'm now trying to figure out how much disassembly is required to get to the other side of this board. After playing for an hour or so, I think I have to desolder and remove the transformers to free it. Seems crazy, but I can't find another way in.
*I cant find wattage of the blown resistors. I know they are 100 ohm mox resisters but 2 what wattage? I can't find a schematic for this thing... from the guy I bought it from or the manufacturer
*I'm taking the tubes to be tested to see if they caused the issue. Will likely replace.
*That only leaves the transformers. Still trying to figure out how to test them.
Thanks for your help so far. I'll come back with what i find next
*I found one bad capacitor. It's a tiny guy placed between two white resistors near the input transformer.
* the rest of the capacitors are ok according to my ESR meter
*I'm now trying to figure out how much disassembly is required to get to the other side of this board. After playing for an hour or so, I think I have to desolder and remove the transformers to free it. Seems crazy, but I can't find another way in.
*I cant find wattage of the blown resistors. I know they are 100 ohm mox resisters but 2 what wattage? I can't find a schematic for this thing... from the guy I bought it from or the manufacturer
*I'm taking the tubes to be tested to see if they caused the issue. Will likely replace.
*That only leaves the transformers. Still trying to figure out how to test them.
Thanks for your help so far. I'll come back with what i find next
Actually, I've worked though a bit of that on my own. Old resistors and caps removed and new resistors and caps on the way. I'm just going to buy new tubes, but before I do that I want to figure out these transformers. If they're all bad, I might abandon the project.
Is there any guidance for testing transformers? I've got them removed from the case, unhooked and......
Is there any guidance for testing transformers? I've got them removed from the case, unhooked and......
OK, guys, PROGRESS
It's all buttoned up and works, but....
One of the front power tubes glows super-orange. Way brighter than the other tubes. I'm thinking that while I replaced what got damaged, I still have the initial problem.
Also I found a schematic which is attached. I've circled the hot tube and marked what I've replaced so far. Any help diagnosing this issue?
It's all buttoned up and works, but....
One of the front power tubes glows super-orange. Way brighter than the other tubes. I'm thinking that while I replaced what got damaged, I still have the initial problem.
Also I found a schematic which is attached. I've circled the hot tube and marked what I've replaced so far. Any help diagnosing this issue?
Attachments
I've replaced all of the power tubes to be safe. I even moved them around. It's always the same position in the chassis that causes the associated tube to glow extra orange.
Check that all of the pins on that socket have continuity to the same pin on the adjoining socket on that leg of the output transformer.
Grids should read 2K pin to pin, if not you've got an open or a bad resistor.
Open grid pin or plate pin can result in some really interesting misbehavior.
Grids should read 2K pin to pin, if not you've got an open or a bad resistor.
Open grid pin or plate pin can result in some really interesting misbehavior.
No,
To pull that resistor I'll have to pull the whole thing apart again, which is fine. But I'm guessing I can't check the voltage with the thing in pieces. To get to the other side of this board I have to desolder all of the connections on the transformers, as well as the volume and signal switches.
Sorry for the noob question, but checking voltage on a pin when idling... Is this just using a multimeter to get a reading on pin 2 while the amp is powered but not turned up or running a signal?
OK, I think I've ruled out any resistor associated with the hot tube. So I guess this brings us to voltage? I still don't have an understanding out how to test this without exploding myself or my amp. I'm going to read up on testing transformers, but if any of you have additional tips I would REEAAALLY appreciate it.
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I've tested each socket for continuity and resistance according to the schematic. I don't think it's a bad connection.
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