Fender "The Twin" Schematic

[Jag]

Anybody have a READABLE schematic for a Fender "The Twin". I can't read the inspetion sticker too clearly but, it looks like 3-3-93 is the ispection date. A number of the components have date codes that look to be from late '92/early '93 so I'm going with that for now.

This was refered to me by a friend. The guy says his son was playing it and it quit working. The amp does not power up at all but the fuses are all fine. I get 120vac going in but nothing at all on any winding on the secondaries. I've only had 5 minutes to check it out, I'll get more into it later and post back.

If anybody has a readable schemtic they could send, I'd relaly appreciate it. Email to jag at jonesong dot com.

[TD_Madden]

http://www.richiholland.com/Red-Knob...atic-parts.pdf

[Don Moose]

Also:
http://www.schematicheaven.com/fende...180w_schem.pdf

Hope this helps!

[Enzo]

Don, that's a Super Twin.

I just put the factory file up on www.ampix.org in the Enzo gallery, but the link TD put up is a cleaner scan than the one on my factury disc.

[Jag]

Thanks everyone! TD's is the best, I can work with that one.

OT primary is open circuit on this amp. Thought it might be the switch but reading across the primary directly comes up the same.

[Don Moose]

Don, that's a Super Twin.

I just put the factory file up on www.ampix.org in the Enzo gallery, but the link TD put up is a celaner scan than the one on my factury disc.

Crap! I backed up too far in the history.

http://www.schematicheaven.com/fenderamps/the_twin.pdf

Not that Jag needs it anymore.

[Mark Black]

Not sure about those amps specifically, but some relatively recent (last couple decades) transformer designs incorporate a thermal fuse somewhat embedded in the windings. These sometimes blow from surges rather than over-temp. If this tranny has that feature the good news is it could probably be replaced, the bad news is it's not easy and involves risky surgery...

I found a bad one recently in a Fender Twin re-issue amp so I know they are around.

[Jag]

Yeah, I was wondering about that. Especially since the fuses are all fine and there are no other indications of problems.

How much surgery is involved? I've heard about the thermal fuse in a tranny but never had to look for one.

[drewl]

I've replaced thermal fuses in GK amps....
find the wires going into (out of?) the tranny and carefully cut away the tape wrapped around the windings and you'll find the fuse.
Radio Shack used to have them.

[Mark Black]

Yup - way careful cutting into the paper wraps, following the primary hookup wires. Actually you might try getting the paper off the ends first - that Twin tranny I did had the thermal fuse tucked into a small tube that was visible when the coil ends were exposed.

If you can follow the primary leads to where they are soldered to the tranny windings look for one that is connected to a larger bright solid wire rather than the brown enameled winding wire - that will be the fuse lead. The other side of the fuse will continue on to the winding.

Radio shack did indeed have those - original was 142 degrees C, the local Rat Shack had one that was supposed to be 140 degrees but in actual fact was marked 144 on the part. Close enough for sure! A search for "thermal" brings them up (along with a few other things).

[Jag]

I won't get back to this until tonight. I've been reading some other posts on the subject of the thermal fuse inside a transformer. Is it a good idea to replace the device or should I still consider the transformer to be toast and replace the whole thing? I've seen mixed opinions on this.

[Mark Black]

I have mixed feelings about those fuses myself, mostly negative. We probably all know fuses can sometimes "nuisance-blow" for no apparently good reason. In the case of these things that adds up to a pretty expensive failure for most people. Maybe if they made them easily replaceable...

Some equipment these days have no external or internal fuses, relying on that transformer fuse instead. That to me is just sick and wrong. Some dbx & Behringer pieces come to mind.

Amplifiers and radios seem to have made it 30, 40, 50 or more years without a thermal fuse inside the transformer. When a tranny went bad - well that's what the mains fuse is there for. Or the mains fuse plus the "secret" internal fuse for those who tin-foil the easily-accessible one in better designs.

In my personal-use stuff I have no problem just bypassing the damn things (because I know I'm not going to tin-foil the external fuse).

All that being said in our litigious society of today you should at LEAST replace the fuse with a similar part if not replace the entire transformer when doing a repair for a customer. Even then we're probably not safe from idiots and/or happenstance plus a well-crafted lawsuit. Everything's got to be SOMEbody's fault after all...

And anyway - it might turn out your tranny doesn't have one of these gizmos in it. Just old-fashioned open.

[Jag]

There's no way I'll get that transformer apart without destroying it. I don't think it has a thermal fuse anyway. Amps such as the Super Twin and Super Twin Reverb, indicate the internal thermal fuse if it has one.

Anybody know where I can get a replacement? Don't see anything similar from the main suspects but I've emailed a guy on ebay who's selling new OEM replacement parts.