Vox Thomas Cambridge SS v1031speaker replacement?

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Vox Thomas Cambridge SS v1031speaker replacement?

Postby jasyr on Fri Aug 25, 2017 1:48 pm

What new 10" speaker do you use for it? Would like a ceramic i think...
& Do I really need to use a 4 ohm speaker for it?...

thanks much,
j
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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby R.G. on Sat Aug 26, 2017 3:08 pm

I personally liked the sound of the Weber "Blue Pup" in mine. Take a look at the Weber speaker site.

You do not have to use a 4 ohm speaker in it, although the power output will be less if you use an 8 ohm. In my dotage I've come to appreciate quality more than quantity - the tone quality of a speaker is more important to me than the loudness. Loudness can be had easily enough, sound quality, not so much.
Best regards,

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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby Zurdo on Sat Aug 26, 2017 8:38 pm

Finally!!! A Thomas Vox question!!

here's another: so if you use 16 ohm speakers when the originals were 8 ohms, you get less volume?
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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby Pitchfork on Sun Aug 27, 2017 9:28 am

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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby R.G. on Sun Aug 27, 2017 3:47 pm

The human ear is a complicated thing, OK. But on top of that commentary on the ear, there are other technical things going on with Thomas Vox amps in particular.

Thomas Vox amps were designed at a time when there were not many good power transistors available. What transistors were available were limited to lower voltages by today's standards, and were limited in "forward biased safe operating area" by "second breakdown". Taken together, the result of these issues came down to a limitation on power supply voltages. Thomas used power supplies peaking at +/-31V in the Buckingham/Guardsman/Beatle series. With no output transformer, this is also the limit on speaker output voltage.

That directly limits output power. If the peak voltage your amp can put on a speaker is "Vpk", and the speaker impedance is "R", the power you can put into the speaker is the peak voltage divided by the square root of two (corrects peak to RMS sine wave voltage) then squared, and divided by R. This is tech-speak for +/- 30V power supplies in a Thomas amp will give you 30W of real RMS sine-wave power into an 8 ohm speaker. If your amp can keep supplying the current, it's also 60W into 4 ohms, and 120W into 2 ohms. It works the other way, too. If you use a 16ohm speaker load with this set of voltages, you get 15W.

The Buckingham and Viscount use two 16 ohm speakers in parallel for 8 ohms, and put out 30W. The Guardsman uses two 8 ohm 12s in parallel for 60W, and the Beatle uses four 8-ohm 12s for a net two ohm load, and 120W.

But back at the smaller amps. The Cambridge and Berkeley 2 use a single and a pair of 10" speakers respectively. The amps are electronically identical, using a single 32V power supply, which has the effect of a +/- 16V power supply. That would be 1/4 of the power of a +/-32V power supply because of that "squared" thing in the math. The Cambridge and Berkeley use 4 ohm speakers, though, to get that back up to about 15W.

The Cambridge does it with a single 4 ohm speaker, the Berkeley with two eight ohms.

Having dragged through all that, we've only computed the >>electrical<< power fed to the speakers. Speaker have widely varying efficiency, that being the amount of sound pressure you get out for an electrical watt into the speaker. Speakers intended for guitar use can have a 20db or more variation in the sound pressure you get for each watt fed to them electrically. That is a ten times variation of the actual sound pressure level you get per electrical watt. On top of that, there is the noted built in compression of the human ear, which converts the 10:1 difference in sound power to an apparent 2:1 difference in loudness as perceived by a human. So for the same speakers, a 100W amp is subjectively "twice as loud". And a 20db more efficient speaker can make the same amplifier sound as loud as one ten times as powerful.
Best regards,

R.G.
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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby Zurdo on Sun Aug 27, 2017 11:32 pm

R.G.,

thanks for the Mandarin Chinese, of course, I didn't understand a word. :D

But Thanks nonetheless. Hope you are doing better. I think my Viscount needs a cap job.

I saw full sets of the caps being sold somewhere, I think it was in Germany, but I can't find them now.
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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby R.G. on Mon Aug 28, 2017 12:16 am

There are lists of the necessary caps posted at geofex.com.
Thanks for concern. It's getting better.
Best regards,

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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby DougH on Tue Aug 29, 2017 1:44 am

I like R.G.'s choice. I used a blue pup in my tube pacemaker and I always liked the way it sounded.

Hi RG, I sent you a PM
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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby Zurdo on Tue Aug 29, 2017 9:41 am

R.G. wrote:There are lists of the necessary caps posted at geofex.com.
Thanks for concern. It's getting better.


downloaded the file, but mine is V1153 ? not shown in the list.
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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby jasyr on Tue Aug 29, 2017 12:26 pm

Thank you for the replies. I live in Germany and Webers are not readily available... alternate please?

I thought I'd also add that I will be playing the VTC SS fairly loud all the time using the volume pot for cleans and the amp for dirty. Is there a speaker ohm/wattage that can be brighter and clear?... Perhaps just a little speaker break-up for the 18 watts of it? Also read the amp is a quiet 18 watts. True?

Noticed 4 ohm speakers reduce my choice... how much will a 8 ohm reduce my volume? ( no story problems please! never finished high school) It is for live gigs.

Will be using the MRB for leads too, so could that razz out a lower watt speaker? I just play these things! After 40 years of bands I've not learned anything of innards of things. I have had this amp since 1980!!

Thanks for any further advice!

j
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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby OldSchoolDave on Tue Aug 29, 2017 12:40 pm

jasyr wrote:I live in Germany and Webers are not readily available... alternate please?


Celestion Blue or Gold would be appropriate but, as you alluded, they only come in 8 and 16 ohms impedence. And, they are NOT cheap...

In the interest of efficiency, what brands ARE available to you in Germany?

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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby jasyr on Tue Aug 29, 2017 2:57 pm

I've bookmarked these around the price for me...100 bucks or so... (I have a Jensen P12 alnico in a cab & want a different flavor.) Also the least amount of compression is high on my priorities. They have Celestion Alnico Gold 10" 8 Ohm for 225 Euros... (is it made in ceramic?)

Kind of a lot, as I'm going to spend some money to get the Cambridge a tune up as well. I estimate that will be around 300$/Euro... as everything is more expensive over here. I do like to get better quality things that will last longer.
The Jensen was around 100 and it was another world from the stock ProJr. speaker i replaced.

My VTC SS compresses early compared say, to my ProJr... maybe a cap job etc. will bring back dynamics if its a tired amp. Dunno. It's never broken down on me yet. Its been thru a lot. I don't know what a maintained one of these sounds like... but always thought it could use more highs. Thought thats why they came up wit the Top Boost? But the amp is a great sound generally!

Anyways

Celestion G10 Greenback 8 (too compressed?) How's the compression compared to a Blue Pup?

Eminence Legend 1028K

Eminence GA10-SC64

Jensen Jet Series Tornado 10" 8Ohm (also is dark) Was interested in the Jensen Mod Series, but it doesn't appear to be available over here.

Eminence Ragin Cajun (but heard its dark.)

Any advice would be very appreciated... cheers!

jasyr
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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby OldSchoolDave on Tue Aug 29, 2017 11:05 pm

On this side of the pond, Thomas Organ used gold (ceramic) Oxfords in some of their cabs.

Since you've got the Alnico thing covered, I'd be tempted to try the Eminence GA10-SC64. Have not heard that one personally, but it looks interesting.

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Re: Vox Thomas Cambridge SS v1031speaker replacement?

Postby jasyr on Thu Aug 31, 2017 1:50 pm

So I've narrowed it down to Celestion G10 Greenback,
Vintage 30,
Eminence GA10-SC64
and the expensive Celestion Gold...
I will report back here after.
Purchasing next week,
not sure if the Eminence at 20 watts will be enough for the Cambridge cab on its own though.

cheers,

jasyr
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