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Post subject: '57 Reissue Twin Troubles
Posted: Sat Dec 07, 2013 4:01 pm
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Not long ago I purchased a used '57 Twin Reissue and until this week it sounded great. Yesterday I went in to fire it up and no sound. I was checking the tubes and noticed that the rectifier tubes aren't lighting up at all and while the other tubes are warm and glowing these two are cold as ice. Obviously replacing them is probably in order but I find it hard to believe that they would both go bad at the same time. Could it be the output transformer? Is there a preamp driver tube I should check? If it was a bad driver or power tube wouldn't the rectifier tubes still light up?

Any advice would be appreciated.


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Post subject: Re: '57 Reissue Twin Troubles
Posted: Sat Dec 07, 2013 4:15 pm
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r2dhart, welcome to the Forum! :D

Your amp has a separate fuse to the rectifiers. Fuse F2. You need to pull the amp from the chassis. Check the positions of *F1 and F2 on second page (page 2 of 5) of PDF file:

* edit: "F1" on the layout of the PDF file is prolly F3. F1 is the main fuse, whcih has it's own fuse holder.


http://support.fender.com/schematics/gu ... ematic.pdf


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Post subject: Re: '57 Reissue Twin Troubles
Posted: Sat Dec 07, 2013 5:42 pm
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Thanks man! It turns out it was the fast acting fuse. A whole lot cheaper than a trip to the amp tech.

Thanks again! :D


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Post subject: Re: '57 Reissue Twin Troubles
Posted: Sat Dec 07, 2013 6:04 pm
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Now you just have to determine what caused that fuse to blow in the first place lest this issue re-occur at a most inopportune moment.

Arjay

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Post subject: Re: '57 Reissue Twin Troubles
Posted: Sat Dec 07, 2013 11:41 pm
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Arjay,

The '57 Twin reissue kept one of the bad pieces of the tweed Twin. Two rectifiers. On cold start owners complained of popped fuses, due to the rapid in-rush caused by the two 3-amp draw 5U4G's. Same thing is prolly happening to the rectifier fuse used in the '57 Twin reissue.

Plus those two 5U4G should be as closely matched as possible. I hear that many tweed owners would just pull the 5U4G's. And insert one nice 5U4GB. The 5U4GB has plenty of voltage and current output, for the original tweed Twin. And should be plenty for the reissue. I wonder why Fender put in two 5U4GB's into the reissue? This is overkill.

http://www.webphix.com/schematic%20heav ... in_5e8.pdf


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Post subject: Re: '57 Reissue Twin Troubles
Posted: Sun Dec 08, 2013 1:05 am
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In that instance it might be prudent to over-spec that internal fuse by perhaps .25A or so -- just enough additional "breathing room" to permit the rectifiers to fully light. Either that or switch those bottles out for types using indirect heaters (the P/S likely would need some mods and/or adjustments to permit that).

Arjay

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Post subject: Re: '57 Reissue Twin Troubles
Posted: Sun Dec 08, 2013 1:21 am
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Arjay, Fender should have put in a slo-blow fuse. I wouldn't recommend this, if the amp is still under warranty. But, it looks like the fuse is 12 amp/250VAC, Fast Blo! I don't understand the logic. The main fuse is 3 amps... :?:


http://support.fender.com/schematics/gu ... ematic.pdf

Going back to the two rectifier issue, it prolly be a more reliable amp if Fender used two UF4007 inline with one 5U4GB. Then, you'd have the tube sag, with having better transient response and life from the tube rectifier.


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Post subject: Re: '57 Reissue Twin Troubles
Posted: Sun Dec 08, 2013 1:48 am
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+1 on both accounts.

The slo-blo fuse would forestall the propensity for excessive voltage surge on the initial light-up. And of course, a pair of inline diodes with a single 5U4GB would certainly provide better HV stability and reliability.

But then the amp wouldn't qualify as a true re-issue (as if it really were one to begin with).

Arjay

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