Silvertone 10xl Speaker Jack - +/- wires

[sywagon]

Hi, first post and not knowledgeable about amplifier workings. I have a Silvertone 10xl and in the process of replacing the baffle for a 10" silver bell I would like to install a speaker jack in the chassis.

I am pretty sure the speaker is wired correctly currently, but I wanted to confirm that before putting in the jack. There are just two uninsulated wires coming out of this thing (output tramsformer?) that were going directly into the speaker, which was not original. There is a red and a blue wire going to it, you can see coming through the chassis.

Can you folks tell by looking which would go to the negative end of the jack, or is there a reasonable way to find out with a meter?






Thanks for looking!

[Tom Phillips]

The power amplifier in your amp is a single ended circuit with no global feedback and neither of the output wires to the speaker is referenced to ground. Therefore, it doesn't make any difference which wire connects to which speaker terminal. Exception: Unless you plan to use the amp in parallel with another amp and you want them both to be in phase. In that case you would need to do some tests to determine which one you would designate as "positive" and "negative / common". You would need more than a meter. I would use a signal generator and a scope.

The original wires to the speaker only have a thin layer of sprayed on insulation to protect them from shorting together. If it were mine I would slip an insulating sleeve on each one and just hook them up directly to the speaker again. If you want to add a speaker jack you would need to add a bracket to hold the jack or drill the chassis for the jack and route the wires back inside the chassis to the jack terminals. I would use an insulating jack to prevent possible problems caused by grounding one of the speaker leads to the chassis. I.e. keep the stock wiring hookup.

Note that I have not mentioned the usual concerns about altering old amps, upgrading to grounded power cords etc.

Tom

[Jazz P Bass]

The two output transformer wires do not really have a polarity, as such.
Just hook them up to the speaker jack.
Silvertone 1421 (Sears 10XL) Tube Amp | Tone Gems

[sywagon]

The power amplifier in your amp is a single ended circuit with no global feedback and neither of the output wires to the speaker is referenced to ground. Therefore, it doesn't make any difference which wire connects to which speaker terminal. Exception: Unless you plan to use the amp in parallel with another amp and you want them both to be in phase. In that case you would need to do some tests to determine which one you would designate as "positive" and "negative / common". You would need more than a meter. I would use a signal generator and a scope.

The original wires to the speaker only have a thin layer of sprayed on insulation to protect them from shorting together. If it were mine I would slip an insulating sleeve on each one and just hook them up directly to the speaker again. If you want to add a speaker jack you would need to add a bracket to hold the jack or drill the chassis for the jack and route the wires back inside the chassis to the jack terminals. I would use an insulating jack to prevent possible problems caused by grounding one of the speaker leads to the chassis. I.e. keep the stock wiring hookup.

Note that I have not mentioned the usual concerns about altering old amps, upgrading to grounded power cords etc.

Tom

Great, thanks!

I will be putting in a grounded power cord while it is out and shrink wrapping the speaker wires. To keep this all completely reversible, I'm making a new baffle for the speaker. There will be room to mount the jack on the baffle so no holes. I want to be able to plug it into a 4ohm 2x12" cab at times.

I do run it in stereo with another amp at times - would this phase thing be noticeable in a bad way?

The two output transformer wires do not really have a polarity, as such.
Just hook them up to the speaker jack.
Silvertone 1421 (Sears 10XL) Tube Amp | Tone Gems

Thanks

[sywagon]

One more question if anyone can help - I want this speaker jack to turn off the internal speaker when I plug in a cab. I found this but I can't figure out if I got the right jack. I ordered the "shorting" jack from Weber (Neutrik PJ-P-S). Now my head hurts trying to figure out if that is a tip shunt or a "switched" type, or what any of that means.

Assuming that I screwed up the order, what is the right "switched" jack in Neutric or Switchcraft to do this:


Kalamazoo Amp Field Guide: Speaker Replacement

[Tom Phillips]

… shrink wrapping the speaker wires…

That would work but other options are:

1. Use insulating tubing. Also called spaghetti tubing.
2. Strip some long pieces of insulation off some scrap wire
3. Just be careful with the existing wires.

… I do run it in stereo with another amp at times - would this phase thing be noticeable in a bad way?..

Yes. If the two amps are out of phase the sound will be thin. You can do a test by reversing the speaker wires in one amp. Which ever way sounds best is the "in phase" configuration that you want to go with.

One more question if anyone can help - I want this speaker jack to turn off the internal speaker when I plug in a cab. I found this but I can't figure out if I got the right jack. I ordered the "shorting" jack from Weber (Neutrik PJ-P-S). ..

OK.Now I understand what you want to accomplish. The diagram you posted will work as you describe and it is showing what is known as the standard mono shorting jack. However, I can’t find a description of the Neutrik PJ-P-S model. (Weber doesn’t show a diagram on their site either. Most likely you have ordered the correct part IMO.

Cheers,
Tom

[sywagon]

Fantastic, thanks so much for your help. Really useful info.

When the jacks come I can post a pic if that would clear it up. I saw they have another version that says "switching" (not at Weber). I may order them as well just so I don't have to sit around when the speaker comes.

Cheers,
John

That would work but other options are:

1. Use insulating tubing. Also called spaghetti tubing.
2. Strip some long pieces of insulation off some scrap wire
3. Just be careful with the existing wires.

Yes. If the two amps are out of phase the sound will be thin. You can do a test by reversing the speaker wires in one amp. Which ever way sounds best is the "in phase" configuration that you want to go with.


OK.Now I understand what you want to accomplish. The diagram you posted will work as you describe and it is showing what is known as the standard mono shorting jack. However, I can’t find a description of the Neutrik PJ-P-S model. (Weber doesn’t show a diagram on their site either. Most likely you have ordered the correct part IMO.

Cheers,
Tom

Anyone interested in a Weber blue pup 8" 8ohms that is nicely broken in and mint condition for a fair price let me know. I bought it new a couple of years back and it has only seen life in this 10W 4ohm unit.

[Jazz P Bass]

You most certainly will need a 'switching' jack.
That is what is shown in the Kalamazoo picture.
The tip is switched.

[sywagon]

You most certainly will need a 'switching' jack.
That is what is shown in the Kalamazoo picture.
The tip is switched.

Sorry if I am stupid - still confused by "switched" and "tip shunt" Does this look right:

Switchcraft "13B 1/4" Stereo 3 Conductor Jack w/Nut & Washer, Tip is Shunt"
http://www.switchcraft.com/Drawings/13B_CD.pdf

Neutric N*J4**
http://www.neutrik.com/zoolu-website.../Jack+Circuits

E.g.
Neutric NRJ4HH "switched"
http://www.neutrik.com/zoolu-website...Drawing+NRJ4HH

[Jazz P Bass]

Switched.
Tip shunt.
Same thing.
The 'stereo' jack is overkill & will only confuse things more.
An unswitched jack is like on a guitar input.
A tip & a ring.(by convention the tip is positive & the ring is ground)
That is all.
A switched jack adds a contact to the tip.
Normally it is closed.
Insert a plug & it opens.
A switch.
(This explanation is simplified. There are many different arraignments of contacts available.)

[Tom Phillips]

Sywagon,

I understand your confusion. There are multiple jacks available and many terms used to describe the various configurations. The jack shown in the Kalamazoo Amp field guide figure in your post #5 is called a mono shorting jack and, depending upon how it is wired up, it can perform a “switching” function. You will find it called both a “shorting jack” and a “switching jack.”

The figure in your post #5 shows such a jack performing a switching function. The classic part number for this jack is Switchcraft 12A. Other manufacturers make equivalent jacks and many other variations. The Switchcraft 13B that you linked in post #9 is a stereo version of the 12A. Your link just shows the mechanical drawing without the schematic so it’s difficult to figure out what you have there for someone who isn’t already familiar with the jack. The 13B would work for your application if you just leave the ring terminal unconnected.

The Neutric N*J4** shown in your second link will work for your application too. It just has an extra switch terminal, labeled SN, connected to the barrel. The Neutric is also an isolated jack because there is no electrical connection from the barrel terminal to the mounting nut.

For some additional information check out the post at http://music-electronics-forum.com/t28549/ which shows a drawing of a jack (there it’s called a “closed circuit” jack so now we have three descriptions so far) and an electrical diagram all in one place. The jack shown in that article is the Switchcraft part number 12A.

Regards,
Tom

[g1]

Just a reminder of what Tom mentioned earlier, the jack should be insulated from the chassis. Not sure now which type of jack you will be using, but a plastic bushing style will provide insulation. Otherwise you can use insulating washers with metal bushing type jacks. This will prevent any new ground loop/hum issues.

[sywagon]

OK, thanks to everyone - you guys are awesome. I think I get how this switch is going to look/operate now.

Unfortunately it looks like it should also be called an "I'm in here messing up your tone" witching Jack? Should I just use a real switch or is that just as likely to get gunked up? I have some of the de-oxit cleaner and the preservative stuff.

[Tom Phillips]

If your only connecting one speaker at a time you don't need a switch at all. Just install jack and wire a plug to the internal speaker. Then just plug in whichever speaker you want to use.

[sywagon]

Just a reminder of what Tom mentioned earlier, the jack should be insulated from the chassis. Not sure now which type of jack you will be using, but a plastic bushing style will provide insulation. Otherwise you can use insulating washers with metal bushing type jacks. This will prevent any new ground loop/hum issues.

Yup - current plan is to have the jack coming through the new baffle (1/4" birch furniture ply I got today). I.e. plug in a cab through the front and the internal speaker shuts off, unplug it to go back to the internal. I don't think it will look too conspicuous in the top right, but as much as I love the thing it isn't a pretty amp to start with. My only concern is that if someone were to plug an instrument jack in it, or unplug the other end from the speaker there would be trouble. Currently no one but me is authorized to fiddle with it though it would also argue for getting a separate switch.