Completely stumped - please help &nb

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yellatele88
Senior tube assistant
Posts: 157
(6/12/05 12:15 pm)
  Completely stumped - please help
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 I'm building a 5f1 Champ using the Weber Champ tranny.

Right now, I have the heater ciruit wired up, and I was testing the voltages. The tubes begin to warm up for about 10 seconds, and them it blows the fuse. I double checked, and I am using a 2 amp slo-blo.

Does this possibly point to a bad PT?

I'm reading:
122V on my AC Mains
4.6V on the 5 volt tap
5.6V on the 6.3v tap
560V on the HT tap.

I have the center taps grounded to the chassis - which has a solid earth ground to the outlet. Could it be something stupid like a bad tube?

Thanks!

Bob
 
 
JayB
Senior tube assistant
Posts: 137
(6/12/05 1:02 pm)
  Re: Completely stumped - please help
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 What does each side of the HT taps read? What is the voltage after the rect? For the heaters, are you using just the center tap and not the 100ohm resistors? What is the bias setting before she blows? I would suspect the rect or the cathode bias circuit. Could be a bad filter capacitor just after the rect. Which reminds me, what value filter cap are you using after the rect. Higher than 20uf?
 
yellatele88
Senior tube assistant
Posts: 158
(6/12/05 1:59 pm)
  Re: Completely stumped - please help
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 The readings I was posting are just from the PT. I have not installed any of the other circuits yet. I have the AC Mains, and the heaters running to the sockets. Is it blowing the fuse because I have the HT going nowhere?

 
GroundhogKen
Moderator
Posts: 2809
(6/12/05 1:59 pm)
  Re: Completely stumped - please help
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 To my knowledge, the Weber Champ power transformer does not have a center tap on the 5V secondary, but if for some reason yours does, make sure it is not grounded.

Do you have any tubes installed? Yank 'em out and try it. Yes it could be something silly like a bad tube or backward caps.

Or try disconnecting one tap at a time and try it.

Use an ohm meter to make sure none of the secondaries has any kind of connection to another or to the primary.

Don't forget to discharge the caps while you're jumping in and out of there.

Ken
 
GroundhogKen
Moderator
Posts: 2810
(6/12/05 2:01 pm)
  Re: Completely stumped - please help
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 The transformer will operate if it is unconnected--just don't let any loose wires touch anything or each other.

Ken
 
yellatele88
Senior tube assistant
Posts: 159
(6/12/05 2:30 pm)
  Re: Completely stumped - please help
--------------------------------------------------------------------------------
 Figured it out - 6 fuses later. One of my 6v6's had a short in the heater, and it was blowing the fuses.

One question I have though - my heaer voltages are show 4.9 volts on both the 6.3V tap and the 5V tap. is there anything I can do to bring the voltages up?


 
GroundhogKen
Moderator
Posts: 2811
(6/12/05 4:42 pm)
  Re: Completely stumped - please help
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 Measure each leg of the 6.3. You should get about 3.1 and 3.1vac. If not, pull some tubes, then it should read slightly higher. Maybe the 6.3 was damaged by the shorted 6v6.

4.9 sounds OK for the 5v winding, but not OK for the 6.3.


Ken
 
LooseChange
I only work on Fender's
Posts: 594
(6/12/05 6:43 pm)
  Re: Completely stumped - please help
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 Hey Yellow...
Yoy need to build one of thse light bulb current limiters.
You won't blow fuses and life will be safer.

 
phsyconoodler
I only work on tube amps
Posts: 409
(6/12/05 8:47 pm)
  Re: Completely stumped - please help
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 If you had a bad power tube,what's to say you don't have a bad 12AX7? It may be drawing too much current,hence the low voltage readings.
 
yellatele88
Senior tube assistant
Posts: 160
(6/13/05 7:53 am)
  Thanks for the help
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 Thanks for all the help everyone. What I forgot to mention was that my 6v6 smoked - literal puffs and a bad smell my pilot lamp. The twisted wires actually melted together. I can only imagine what happened inside the transformer.

I emailed Ted, and ordered a new power tranny and a brand new 6v6. If anyone wants this burnt tranny email me and it's yours. The HT seems to still work.

silvr137 -no e in silver- at hotmail.com

  
 
 
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