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Post subject: 79 Champ Question
Posted: Tue Sep 17, 2013 11:55 am
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Hi,

Just to satisfy my curiosity, can anyone tell me what the diodes next to the power transformer are for? Looks like a rectifier cct to me, but what purpose does it serve if the 5Y3GT does that job already?
Can't see them on any circuit diagrams, unless the export model is different!

Just curious really

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Post subject: Re: 79 Champ Question
Posted: Tue Sep 17, 2013 12:26 pm
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Fender did not put those diodes there.

Arjay

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Post subject: Re: 79 Champ Question
Posted: Tue Sep 17, 2013 1:37 pm
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Someone tried a solid state rectifier at some stage maybe? (looks like its been there for a long time) One of the wires from the transformer is still attached to it, but the amp works ok. Just seems a bit bizarre


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Post subject: Re: 79 Champ Question
Posted: Tue Sep 17, 2013 2:03 pm
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That'd be my guess. Perhaps a previous owner didn't have access to any 5U4GB's when it came time to replace a dead rectifier......?

Arjay

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Post subject: Re: 79 Champ Question
Posted: Tue Sep 17, 2013 2:20 pm
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Retroverbial wrote:
Fender did not put those diodes there.

Arjay


+1

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Post subject: Re: 79 Champ Question
Posted: Tue Sep 17, 2013 2:41 pm
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All three of those wires should be grounded, and wouldn't be used for the rectifier circuit at all. :?

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Post subject: Re: 79 Champ Question
Posted: Wed Sep 18, 2013 12:17 am
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Thanks for the replies, appreciate it.

One end or the rectifier is grounded, so that wire is to ground in-a-way......


Last edited by Mike73JM on Wed Sep 18, 2013 1:31 am, edited 1 time in total.

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Post subject: Re: 79 Champ Question
Posted: Wed Sep 18, 2013 12:30 am
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It looks like all of the diodes are in series, and that both ends of the string are connected to ground. Is the other end connected to the last terminal also connected to ground (chassis)?

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Post subject: Re: 79 Champ Question
Posted: Wed Sep 18, 2013 4:23 am
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There are 5 diodes in series. One more than what would be needed for a FWBr. And the CT of the PT secondary appears to be soldered to the positive end of one diode.

These appear to be pretty heavy duty diodes. Much above the 1amp rated one needed for rectifying a Champ's PT.

Very odd. :?:


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Post subject: Re: 79 Champ Question
Posted: Wed Sep 18, 2013 7:29 am
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BMW2002Ti wrote:
These appear to be pretty heavy duty diodes. Much above the 1amp rated one needed for rectifying a Champ's PT.


+1

That array of diodes would be just about sufficient for a Twin Reverb or a Dual Showman.

Arjay

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Post subject: Re: 79 Champ Question
Posted: Wed Sep 18, 2013 1:07 pm
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I'll check that later, too busy enjoying the Jensen speaker upgrade and the DoD FX22 that arrived today ;-)


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Post subject: Re: 79 Champ Question
Posted: Wed Sep 18, 2013 2:30 pm
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If any event, the solid-state diodes on that terminal strip are doing nothing, but looking pretty.


:D :mrgreen: :D


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Post subject: Re: 79 Champ Question
Posted: Fri Sep 20, 2013 2:07 am
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I'll just leave it be, the amp works fine so I aint messing with it!
That new Jensen speaker sure makes a difference, proper nice :-)
The original speaker still looks like new, always handy to keep I guess


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Post subject: Re: 79 Champ Question
Posted: Fri Sep 20, 2013 11:16 am
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Retroverbial wrote:
BMW2002Ti wrote:
These appear to be pretty heavy duty diodes. Much above the 1amp rated one needed for rectifying a Champ's PT.


+1

That array of diodes would be just about sufficient for a Twin Reverb or a Dual Showman.

Arjay


Maybe it's the 100 watt mod for the Champ! :lol:

That tube rectifier is part of the magic of the old Champs. The sag and compression makes that tone. When you run the Champ through a couple of 12's, you'll see the fire breathing magic. :wink:

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Post subject: Re: 79 Champ Question
Posted: Sat Sep 21, 2013 1:27 am
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Yeah that string to ground is quite interesting! I can see a flyback reasoning at the lower end. But the idea on the North-Bound side, loses me. The thing is, that it is way too deliberate, to disregard! Someone had a good reason to route the CT through this circuit!!! Hey Steve, thanks for gettin' me back to Merlin's tutorials. Playin' is all that I've been up to('cept a tube swap, here and there)! Art

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