TR120B speaker help!

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TR120B speaker help!

Postby (kennyhowes) » Sun Jun 11, 2017 4:05 pm

Blew the speaker in my amp, took it out - and its from Radio Shack. Humph.

Anyway:

- What was OEM in these?

- What's the correct impedance?

- As I took it out of the cab, the purple and yellow + and - wires fell off their lugs. Which one is the + and which is the - ???

Thanks folks!
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Re: TR120B speaker help!

Postby (kennyhowes) » Mon Jun 12, 2017 12:49 pm

According to the back panel, its 4Ω. So that part is solved.
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Re: TR120B speaker help!

Postby (kennyhowes) » Tue Jun 27, 2017 2:28 pm

Ok, so I found a 200w, 4Ω speaker. It's on it's way.

(I also looked up the rating on the Radio Shack speaker that had been in there...50w at 8Ω. No wonder it got wonky!)

Still don't know which of the wires is plus and which is minus.
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Re: TR120B speaker help!

Postby (kennyhowes) » Tue Jun 27, 2017 2:43 pm

So according to this (TR35B, which is close enough):
http://www.rickenbacker.com/pdfs/19342.pdf

...the hard-wired speaker jumps off of the external speaker jack.

So if I look at that jack, I should be able to see which colored wire is the positive and which is negative, and hook them up appropriately to the speaker.

Ok, then.
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Re: TR120B speaker help!

Postby (jps) » Tue Jun 27, 2017 9:00 pm

As there is only one speaker driver in the amp it doesn't really matter what the polarity is. That would only come into play if you were to connect an extension cabinet to the external speaker jack.

What speaker did you find to put in the amp?
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Re: TR120B speaker help!

Postby (kennyhowes) » Tue Jun 27, 2017 11:43 pm

jps wrote:As there is only one speaker driver in the amp it doesn't really matter what the polarity is. That would only come into play if you were to connect an extension cabinet to the external speaker jack.

What speaker did you find to put in the amp?

I read on the internet - so it must be true! - that the polarity in a single speaker combo will likely be correct if the bass response is better. That is, try it one way, then try it the other way, and see which has the better low end. Opinions are welcome.

The one I found is the replacement driver for this cab:
http://harbingerproaudio.com/product/aps15/

Not OEM, but as it's 200w, and the correct impedance, I should get plenty of headroom.

I bet the Radio Shack speaker would be fine in a TR35B amp, as its 50w. Anyone want a cheap (and probably functioning) Realistic 40-1319 15" speaker?
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Re: TR120B speaker help!

Postby (jps) » Wed Jun 28, 2017 12:32 am

I suppose there is a "psychology" to which polarity sounds better, so that's worth a shot. 8) It won't harm the amp at all, either way the speaker is connected.

Is this a harbinger of things to come? :mrgreen: Is the TR35B a sealed, or, ported cabinet? That could make a difference in how well the speaker driver will work in the amp. There is some actual science behind mating a cabinet with a suitable driver.
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Re: TR120B speaker help!

Postby (kennyhowes) » Wed Jun 28, 2017 6:43 am

jps wrote:I suppose there is a "psychology" to which polarity sounds better, so that's worth a shot. 8) It won't harm the amp at all, either way the speaker is connected.

Is this a harbinger of things to come? :mrgreen: Is the TR35B a sealed, or, ported cabinet? That could make a difference in how well the speaker driver will work in the amp. There is some actual science behind mating a cabinet with a suitable driver.

The TR35B and the TR120B are both sealed cabs. I have one of each amp; the 120 is the one in question. The 35 sounds awesome as-is.

I just realized I could always check the polarity wires on the 35 and see if they're purple and green, and which goes where. Duh. I'll just do like I said and check them from the aux speaker jack, since I have the 120 apart.
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Re: TR120B speaker help!

Postby (kennyhowes) » Mon Jul 03, 2017 9:44 am

Update:

1. The purple is the "+" wire. So, there you have it.

2. Replacement speaker arrived damaged. Waiting for advisement/replacement from seller.
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Re: TR120B speaker help!

Postby (admin) » Tue Jul 04, 2017 3:14 pm

Thanks for the information Kenny. :)
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Re: TR120B speaker help!

Postby (iiipopes) » Tue Jul 11, 2017 11:44 am

If the hard wired speaker takes off parallel from the speaker jack, and the jack is labeled 4 ohms, wouldn't that be total load, so you should have an 8 ohm speaker internally and, if desired, an 8 ohm extension cab? That would be consistent with most of the power transistors of the day.
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Re: TR120B speaker help!

Postby (jps) » Tue Jul 11, 2017 12:40 pm

Yes, Scott is correct. The internal speaker needs to be an 8 Ohm unit.
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Re: TR120B speaker help!

Postby (iiipopes) » Tue Jul 11, 2017 5:49 pm

Jeff - thanks.

Some of the newer solid state amps of other manufacturers, like some of the smaller Vox amps, are different in that the speaker jack has a disconnect finger to the internal speaker when an external cab is plugged in, so that it is effectively an either/or situation, not both in parallel, like older Fender (true parallel), Marshall (various configurations) and Ampeg (SVT second speaker jack has a finger that taps a different winding on the output transformer depending on load) amps.

The point being is I forgot to ask: is the jack a true old-style parallel, or a newer either/or? If an either/or, then yes, you could run a 4-ohm internal speaker so long as you don't try to defeat the finger in the either/or jack.

My little Vox Pathfinder practice amp has an either/or speaker jack and an 8-ohm internal speaker. I looked up the "white paper" on its output transistor, saw that it was rated for @ 17 watts and a 4-ohm load. I then jumpered the finger on the speaker jack to run both internal and external in true parallel, with the internal speaker being an 8-ohm speaker, and the external speaker also being an 8-ohm speaker, but just as important, with a similar power rating and compliance.
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Re: TR120B speaker help!

Postby (kennyhowes) » Thu Jul 13, 2017 11:38 pm

Well ****. I went and got (and installed) the replacement* speaker...which is 4Ω.

Works good so far.

Bearing in mind that this is a transistor amp, am I risking any damage by sticking with this setup? What are the downsides?


*Repalcement for the damaged one, that is.
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Re: TR120B speaker help!

Postby (jps) » Thu Jul 13, 2017 11:49 pm

No issues, so long as you do not use an extension cabinet with the amp.
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