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Re: Old amp blows fuses with no tubes in: fault of rusty

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1/30/2006 5:58 PM

Re: Old amp blows fuses with no tubes in: fault of rusty

Hmmm... Looks like a dud transformer however again
I would suspect the .05/600volt cap to ground and
would try it without it connected.
I am assuming you are using a 3 pin mains plug thus grounding the chassis via the power (wall) outlet.
Correct me if I'm wrong but in the states it was common to have two pin plugs thus the chassis was referenced to the neutral (cold ? ) via the
capacitor.
Here in Aust (land down under) all fenders
in the old days had a 3 wire Acive,Neutral and earth
power lead fitted often leaving the capacitor wired to a single pole changeover switch which i deduced was to help eliminate buzz or hum coming through the power (crude filter). However as we use 240 volts here the caps sometimes broke down so it was common place to remove them .
Good luck , be carefull and play safe.. !

1/31/2006 10:39 AM

quote:
"Looks like a dud transformer"

What readings should I expect from the PT secondaries disconnected from the rest of the circuit?

[QUOTE]I would suspect the .05/600volt cap to ground and would try it without it connected.
I am assuming you are using a 3 pin mains plug thus grounding the chassis via the power (wall) outlet.[/QUOTE]

Yes,
I have installed a three-prong cord (Italy here). Mains is 240VAC.
I thought that I could trash the .047 cap from the fuse holder to ground, but I was not sure...

Carlo

1/31/2006 7:54 PM

You really need to have an identical transformer to compare with
However I measured the amps I have here at the moment
1.Vox AC 10 = 13 ohms
2.Australian 60's Maton (2 x EL34 )=19 ohms
3.Fender CBS Champ =24 ohms
These are all wired for 240 volts

I would definatly remove the .47 cap.
Also with the amp unplugged measure between the 2
240 wires (one at a time) and ground in case there is a internal short to the chassis.

I have never seen one in this neck of the woods.

I thought they were only made for the american market thus only had the 120 volt tapping as the only schematics I have seen show this.

But I presume it has 2 x 120 volt windings in series.

Good luck

2/1/2006 1:32 AM

Cap removed: fuse still blows!

quote:
"I would definatly remove the .47 cap"

I did remove it (it's a .047). The fuse still blows after 2 seconds!

Carlo

2/1/2006 7:56 AM
Peter	If everything else is disconected on the secondarys including the 2 earth wires I'm sorry to say its time to buy a new one. Take it to a repair shop for a second opinon or just buy a new one maybe a Fender Deluxe replacement would do but again check with a tech who can do it. A similar problem:- http://forum.duncanamps.com/viewtopic.php?p=393&sid=ef3a18e52d839c51cf029801db70e0f1

2/3/2006 7:29 AM
R.G.	Like I said, open the PT primaries. If the fuse still blows, it's the AC wiring. If not, it's the PT.

1/31/2006 4:48 PM
R.G.	Re: Old amp blows fuses with no tubes in: fault of rusty If you're sure the secondaries are actually open, then yes, it's in the AC mains wiring or the transformer itself. The TADP will nail it for you then. The next step is to open one transformer primary lead. Then try. If it still overcurrents, the AC wiring is fouled. If it does not, the transformer is bum.

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