SF Twin 135 speaker output wiring

[Zouto]

Hello, there's something wrong with my SF Twin 135's speaker output jack wiring. Using the "SPEAKER" jack there's no signal at all, on the "EXT.SPKR" jack it works. The complicated switching jack wiring looks absolutely stock, so what could be wrong?
Thanks for hints'n'help,
Zouto

[Leo_Gnardo]

The switching jack on the ext speaker output may be stock, but it may also be the contacts allowing signal to reach the main speaker jacks - aren't making contact. Bent, corroded, or burnt. If you intend to use the amp only with its built-in speakers you can remove that fancy-dan jack, dead-end the 2 ohm wire, and attach the 4-ohm wire to your main output jack.

Similar situation in the SVT - see "8R load for an SVT" thread, appearing now.

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edit: Oh whoops, yes they are series, my bad. Other than that, same solution, unless you plan to use the ext. speaker jack.

[Jazz P Bass]

The Ext jack uses the Grn & Blk winding.
It gets Blk from a normally closed contact in the Main jack.
The Main jack uses the Grn/Ylw & Blk winding.
The Ext jack has contacts that must be made when the jack is empty.
Those contacts are what supply the Main jack Green/Ylw wire.
Link: Prowess Amplifiers - Fender - Schematics - Twin Reverb sf 135

[pdf64]

The sockets are arranged in series, the complex switching jack arrangement changes between 4 and 8 ohm taps depending on whether the ext speaker socket is in use.
http://www.webphix.com/schematic%20h..._135_schem.pdf
My guess is that one or both of the socket assemblies have rotated a little, such that a terminal is shorted to the chassis.
Most likely the node between the 'sleeve' of the ext socket and the 'tip' of the speaker socket.
Pete

[Zouto]

Thanks a lot for help, unfortunately up to now I could not find any unwanted shorting. Removed, checked and cleaned both jacks for no bettering. I think, I'll use the ext. jack and leave the main jack alone.

[g1]

Is this a problem that just started, or was it ever working right? Any chance someone swapped around the jacks into the wrong holes?
I think the speaker jack would be more "basic" looking than the ext.spkr. jack.
A picture would be very helpful here.

[Zouto]

Is this a problem that just started, or was it ever working right? Any chance someone swapped around the jacks into the wrong holes?
I think the speaker jack would be more "basic" looking than the ext.spkr. jack.
A picture would be very helpful here.

Right, the speaker jack is the simple switching type, the ext. is the complex switching jack, looking like sorta SG toggle switch.

[Jazz P Bass]

With nothing in the Ext jack, plug a guitar cord into the Main jack.
Now read the resistance across the tip & the ring.
If you get an open circuit reading, then either the tranformer wire is not making a good solder connection at the jack, or the winding is open.

[Zouto]

Thanks, I get 1.0 Ohms on main Speaker and 1.2 Ohms on Ext.jack, using my trusty Fluke 87 V. Otherwise the amp sounds fine using the Ext. jack.with the built in speakers (4 Ohms). I'll ask a friend to check the output resistances on his Twin135.

[Jazz P Bass]

O/K.
Now try the same test but go tip to chassis.

[g1]

Possibly the shorting contact/switch in the ext.spkr. jack is reading closed with the ohm meter but not passing current?
Can you try shorting across the switch in the ext. spkr. jack?

[Jazz P Bass]

Have to agree.
The Main jack Grn/ Ylw winding wire literally goes through the Ext jack normally closed contact.
All the Ext jack needs is Main jacks normally closed ground connection.
Still could be a funky winding.

[g1]

A jumper wire from the green/yellow wire contact on the ext.spkr. jack to the hot terminal of the spkr. jack should make the spkr. jack work if the ext. jack switch is the problem.

[Zouto]

A jumper wire from the green/yellow wire contact on the ext.spkr. jack to the hot terminal of the spkr. jack should make the spkr. jack work if the ext. jack switch is the problem.

Yeah, I jumpered it, no fix, dead quiet, still no sound. Next I'll probably gotta check the OT taps separately, unsolder 'em etc.etc.......

[pontiacpete]

This is probably a different scenario but,
I have a 135 twin here that wasn't make sound out of the main speaker jack, turned out the shorting switch on the jack was touching the tip even when plugging into it.
Bent it back and it worked.