Discussion in 'Amps & Cabs' started by RVA, Nov 14, 2015.
In my quest to understand electronics, amps, guitars, test equipment etc, there is a crapload that is above my understanding, but with videos like these, the principles and the diagramming begins to make sense as far as how components are denoted and the logic behind how to test them etc.
Thank you very much. This certainly helps demystify things. I may try to tackle this again after all!
RVA, just make sure you adhere to the Safety video on how to discharge filter caps and stay safe.
Also, watch that Mr Carlson video pretty closely on how he diagnosed the overpowering of the caps that control the power tubes. It was very interesting to see how he pinpointed the bad cap and then sought to find the culprit on what was causing the failure.
Thanks chili. I am watching and comparing as we speak. Could you fellas take a look and verify what I am seeing? So far I cannot decipher what I see in the schematic, but so far I have identified these caps as per the photos. I think that since it is a 27 year old amp, it could not hurt to change them all.
100uf / 350V / M85 C / ID#s 8802 / LUGM / 8N08AC (x4)
50V / 1000uf / negative black / ID # 82T07 (x1)
RVA, so it was one of the 6l6's that blew up huh. I see the amp has a buttload of 12 ax7's and a couple 12at7's. If my understanding of figuring out your problem sits straight , there is something causing excessive current to 1 blow the fuse and 2, mess up your 6L6. To do the diagnosing, I would have to stress the need to discharge the caps first. Then of course check for absence of current, and then check for leakage.
If you don't understand leakage and how to test caps, plenty of youtube vids tell how. I think I posted some.
I can't tell you better at this point in my knowledge of things by looking at your pics, but only from my own Marshall, Laney, Fender amps experiences I can say in the end if you do discharge your caps and test the resistance, I believe it should read 0
If there is leakage, you will get a positive number of ohms and know that cap is bad.
Now what caused it to go bad is still to be determined, Age, other voltage excesses etc. This is the million $ question.
Also, bro, Voxy, Don etc all have good advice. I'd definitely be posting at Peavey forum too and doing my best to get this sorted by coming up with a plan that starts as testing the root of the problem by learning how to read schematics, and how to use test tools to take your readings to see what parts are in spec or out
So unlike the caps in the video, these are on a pcb board. Does this present any unique issues when testing?
Give me a clear photo of your 8 pin power tube sockets on the board side make sure that the grid resistor's read 470 ohms should be 5 watt
Then I will walk you through a voltage check on the 8 pin sockets. That will determine if you have a transformer issue.
I know cold solder joints were mentioned earlier. With your best eyes and extra magnification, and really good lighting, gently rock those tubes in their sockets, and focus on the solder side of each pin while rocking. Do you see any separation within the solder? Talkin about a 1000th of an inch!
Like 67 plexi said,,,,,, do that and see how it plays out.
I also found a real good layout of a Champ amp and it really seems like having clear markings of parts and colored wiring laid out helps if figuring out how each part does it's thing.
That is much easier to read than a schematic (at least for me)- Thank you. The video on how an amp works was also a great overview. I believe I need a cap tester for this and in general.
RVA you should be fine with a multimeter
The very very most important rule of working on high voltage stuff is to ALWAYS keep that one hand in your pocket. It helps keep you from becoming part of the circuit.
Like 67 says,
I'd like to see the sockets, overall layout, and board side...
then learn what 67 means by "make sure that the grid resistor's read 470 ohms should be 5 watt"
another pic with el84's,,,, these point to point amps like my Marshall make sense to me,,,,,,,,,, I am pretty sure PCb ones will too as I go slow as I would trace the routes the currents follow on the boards in similar way they go similar to these components shown.
Separate names with a comma.