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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 21st Sep 2019, 3:19 pm   #81
ms660
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Default Re: Convert Vintage Valve Radio to Guitar Amp

Excellent.

Lawrence.
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Old 21st Sep 2019, 3:35 pm   #82
davebms
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Default Re: Convert Vintage Valve Radio to Guitar Amp

hello all, just watched the video ,,impressive
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Old 21st Sep 2019, 4:03 pm   #83
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Default Re: Convert Vintage Valve Radio to Guitar Amp

Amazingly, I measured 106 dB 1 metre away from the speaker (albeit using a phone sound app, so probably not the most accurate).

Quite how such a low power amp is capable of putting out that sort of power, I don't know!
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Old 21st Sep 2019, 8:27 pm   #84
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Default Re: Convert Vintage Valve Radio to Guitar Amp

It's a matter of having a much more efficient speaker than you may be used to. High quality speakers are monumentally inefficient so what a speaker optimised for efficiency can do is surprising.

As a reference, a trombone played flat out is pretty noisy, and the acoustic power out of it is about half a watt.

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Old 21st Sep 2019, 10:52 pm   #85
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Default Re: Convert Vintage Valve Radio to Guitar Amp

Cheers!
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Old 21st Sep 2019, 11:03 pm   #86
Paul JD
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Default Re: Convert Vintage Valve Radio to Guitar Amp

Quote:
Originally Posted by robbo100 View Post
Quite how such a low power amp is capable of putting out that sort of power, I don't know!
Don't confuse power output with sound pressure level (SPL), as David said above the biggest effect on SPL will be speaker efficiency, not the output power of the amplifier. A typical HiFi speaker might have an efficiency of 85 - 90dB (this means that if you feed the speaker with a 1 watt signal and measure the SPL at a distance of 1M it will be 85 - 90dB). A typical radio or guitar amp speaker will have a much higher efficiency as there is a trade off between "sound quality" and efficiency, most guitar speakers are 95 - 100dB.

To put this into context it takes an increase in SPL of around 10dB to produce a perceived doubling of volume (dB is a logarithmic scale) so by changing the speaker in an amplifier from a 90dB to a 100dB you can double the volume. To achieve the same doubling of volume by increasing the amplifier power you would need to increase the power by a factor of 10 so if your original amp was 5 watts you would need to increase that to 50 watts to double the volume.
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Old 22nd Sep 2019, 1:53 pm   #87
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Default Re: Convert Vintage Valve Radio to Guitar Amp

That is one vintage radio that will get used unlike most restorations where the "it's going now" is all that happens.
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Old 27th Sep 2019, 7:35 pm   #88
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Default Re: Convert Vintage Valve Radio to Guitar Amp

That sounds great!

I too would be interested in what set of valves your Cossor uses. I have a 501 in use and a 500 (the woodie) non-worker for spares which might be interesting to apply to this purpose - I think both of mine use rimlock valves.
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Old 27th Sep 2019, 8:45 pm   #89
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Default Re: Convert Vintage Valve Radio to Guitar Amp

Interesting explanation of power, volume and sound pressure levels here.
http://www.sengpielaudio.com/calculator-levelchange.htm

Mike
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