#1
Ok so I built a handwired JCM800 2204 from ceriatone and Its been wroking fine for about 9 months. Then one night at rehearsals it just died on me. SO i check the HT fuse and it was fine. Then I checked the mains fuse and it was blown. So i replaced it with the same rated fuse as the previous which is a 3amp slo blo. It immediately blew. So i took all the tubes out and tried again. Same result. Then i did some other tests and unhooked the 325V secondaries and tried again. Blown fuse number 4. Thne I unhooked the heaters. Guess what? Blown fuse. So I can only assume that my primaries are shorted on my transformer. Would that be safe to say?

But what my real questions is how does one blow a Primary transformer? There were no astorms or strange power surges while playing or prior. I just want to know so I mke sure i dont have this problem when I get a new PT. Any ideas?
#2
Have you used a multi-meter to check the PT?
You can check the primary and secondary windings, and also check for the windings shorted to each other and the chassis (ground).
Also have you checked your wiring from the mains inlet to the PT? Is anything shorted to ground or anything else?
Depending on where your HT fuse is in the circuit the rectifier or primary filter cap may also be shorting out. Again these can be checked with any good multi-meter.
#3
Quote by PaoloJM
Have you used a multi-meter to check the PT?
You can check the primary and secondary windings, and also check for the windings shorted to each other and the chassis (ground).
Also have you checked your wiring from the mains inlet to the PT? Is anything shorted to ground or anything else?
Depending on where your HT fuse is in the circuit the rectifier or primary filter cap may also be shorting out. Again these can be checked with any good multi-meter.

I have a good multimeter but im unsure how to check the primaries. Does it need to be plugged in and turned on? I checked the secondaries and the heaters and they are still in circuit. I'll double check the mains wiring again. but everything seemed good. Here is the layout i used for this.
http://www.ceriatone.com/images/layoutPic/marshallLayout/JCM800_2204Ceriatone.jpg

Thanks
#4
Quote by migs_migeezie
I have a good multimeter but im unsure how to check the primaries. Does it need to be plugged in and turned on? I checked the secondaries and the heaters and they are still in circuit. I'll double check the mains wiring again. but everything seemed good. Here is the layout i used for this.
http://www.ceriatone.com/images/layoutPic/marshallLayout/JCM800_2204Ceriatone.jpg

Thanks


Oops, good thing you checked!!
I meant checking them for DC resistance, this will tell you if winding are shorting.
For this the amp need to be turned off and filter caps discharged.
Placing the meter in the low ohm range you can measure the DC resistance across the primary connections. You should measure between 20 and 200 ohms. This would be normal. If you get 0 ohm then you have a shorted primary.
You can can check primary to secondary, secondary itself, primary to chassis and secondary to chassis this way. If any of these read 0 ohms then your PT is the problem. If not then you should go and double all your wiring on the primary and secondary sides as well and the secodary.
You should also buy or build a current limiter so you can test your amp without continually blowing fuses.

If all of this is above your head then you really ought to take it to a tech.
#5
Quote by PaoloJM
Oops, good thing you checked!!
I meant checking them for DC resistance, this will tell you if winding are shorting.
For this the amp need to be turned off and filter caps discharged.
Placing the meter in the low ohm range you can measure the DC resistance across the primary connections. You should measure between 20 and 200 ohms. This would be normal. If you get 0 ohm then you have a shorted primary.
You can can check primary to secondary, secondary itself, primary to chassis and secondary to chassis this way. If any of these read 0 ohms then your PT is the problem. If not then you should go and double all your wiring on the primary and secondary sides as well and the secodary.
You should also buy or build a current limiter so you can test your amp without continually blowing fuses.

If all of this is above your head then you really ought to take it to a tech.


ah I see. Ok that makes sense. Yeah I think I actually may have a current limeter in my house somewhere. My folks use to use for for electrical stuff. thanks I'll check it out and let see what i get.
#6
where do you live / what is the mains voltage?
also, what version is this amp? 100w or 50w?
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#7
Quote by SomeoneYouKnew
where do you live / what is the mains voltage?
also, what version is this amp? 100w or 50w?


Its the 50w version. I live in the US so i have the voltage setting on the 120V setting.
Last edited by migs_migeezie at Sep 14, 2009,