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Post subject: 68 princeton black and blue
Posted: Fri Dec 08, 2017 3:34 pm
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:?: the promotional material says that this is the same circuit as the silverface version but with an upgraded 12 alnico blue. But it’s advertised as being 15, not 12 watts. If it shares the same circuit, how is it a higher wattage? just looking for clarification... :idea:


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Post subject: Re: 68 princeton black and blue
Posted: Sat Dec 16, 2017 8:46 pm
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They can use the same circuit and just up the B+ voltage coming out of the power transformer.
It could also lower the impedance of the output transformer and gain a few watts.
The old silverface might have a 120 vac input rating. A modern one is probably 125 vac. Just this minor difference could account for a few watts.


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Post subject: Re: 68 princeton black and blue
Posted: Sun Dec 17, 2017 2:46 am
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TimsAudio wrote:

The old silverface might have a 120 vac input rating. A modern one is probably 125 vac. Just this minor difference could account for a few watts.


Mine have 117 vac
I guess fist SF may have 115 volts.
Pardon me TimAudio, don't you think with any input voltage ( 117 ,120 or 125 vac ) at the power transformer and with proper winding, we can have same output voltage ?

See export model switchable from 120 vac to 240 vac .
________________________________________
Same post from Dyquen 9 dec

;https://forums.fender.com/viewtopic.php?f=13&t=108713


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Post subject: Re: 68 princeton black and blue
Posted: Sun Dec 17, 2017 11:04 am
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No links to the promo material that supposedly says 15 watts. All the other links say the normal 12 watts.

Retailers sometimes get the specs wrong.

Also possible the promo referred to the 15 watt rating of the Alnico Blue, and OP just misunderstood.

Any changes to a product's circuits requires a whole new round of EU/UL/CSA certifications. Doubtful Fender would go through that for a few watts on a limited run FSR amp. Typically they just change cosmetics and/or get a different speaker.


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Post subject: Re: 68 princeton black and blue
Posted: Sun Dec 17, 2017 11:13 am
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The 117 and 120 volt versions both show a 420 volt b+, so some compensation in design was done then.
The modern spec here is 125 vac. I can't find the 68 schematic, but I suspect it will also spec a 420 b+.
But if you plug in an old amp, it will put out more than it was designed for.
The output of the amp is dependent on the wall voltage.
I can run an amp up to the edge of clipping and turn on the space heater by my feet and now its into hard clipping. Just by lowering the wall voltage a bit.


The difference of 12 or 15 or 18 watts is a miniscule change.
The radiated energy from an amp follows the inverse square law. That is to double the radiated power at any particular distance, you need to square the power.
So to double the volume of a 5 watt amp, you need 25 watts. To double that, you need 625 watts.
Then efficiency comes into play.
You can look at the b+ of a deluxe reverb 868 and see its the same as the princeton. Yet it puts out more power. This is a function of transformer efficiency.
Then speaker efficiency can make an amp much louder than one with more watts. Compare the sensitivity specs between speakers. A 6db difference is twice as loud.


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Post subject: Re: 68 princeton black and blue
Posted: Wed Dec 20, 2017 11:00 pm
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Thanks for the insights folks. Sorry for not replying earlier: I thought my application was still pending. Plus, I've been rocking out with my new amp. The missing (or extra ) 3 watts is of no consequence at all...


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