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Old 22nd March 2005, 01:25 AM   #1
rmihai is offline rmihai  Canada
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Default Advise for my first tube amplifier, please

Hi all,

I need your qualifid advice. I am looking to build my first tube amplifier and I have no clue about how much power do I need.

My speakers:
Sensitivity 84db
Impedance: 8 ohms and dip as low as 6.2 in the bass region
SPL: 90 db

My room: 18 x 20 feet (5.4m x 6.1m); 8 feet tall (2.4m)

Everything I need is 90db loudness, no more. But I really need this 90db to be the most accurate.

So,
How much power do I need?

Thank you for your time
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Old 23rd March 2005, 01:30 AM   #2
rmihai is offline rmihai  Canada
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Old 23rd March 2005, 02:12 AM   #3
james_b is offline james_b  United States
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Default amp recommendations

Hi, if your speakers are rated at 84 db sensitivity I think thats a little below what most tube amps require. If you post what speakers you have someone else may have experience with the same speakers and tube amps and can give you a better answer. Also helpful would be what your budget is for the amp. You may find yourself wanting new speakers too, that will match well with a tube amp.
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Old 23rd March 2005, 03:45 AM   #4
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This web site may help.
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Old 23rd March 2005, 01:01 PM   #5
rmihai is offline rmihai  Canada
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Old 25th March 2005, 01:05 AM   #6
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Getting some more efficient scpeakers would be a great option, but you could also look into getting a more powerful tube amplifier. I recommend something with push-pull pentodes. Try for at least a quad (push pull parallel) of 6BQ5/7189/EL84 tubes, or at least a pair of 6l6 or EL34 type tubes. make sure that the amp has a decent amount of negative feedback (I like amps with local feedback around the output stage, such as ultralinear or cathode feedback, with a lower amount of global NFB) since your speakers obviously aren't designed with tube amps in mind and might have a crazy impedance vs. frequency plot. Remember that tube watts are generally considered to be "worth more" than solid state watts because tube amps will clip more gracefully, and because tube amps are rated in genuine RMS watts, while many consumer amplifiers might have exagerated specifications.

I am not a very big fan of triode amps or single ended amps. You need very efficient spekeakers to run these small amps at decent volume levels.
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Old 25th March 2005, 01:46 AM   #7
amperex is offline amperex  United States
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You need more power than 90dB listening level calls for. At least 30 watts of Class A power for some headroom is needed. Cheapest tubes are 807s & they sound very good triode connected. A quad of 807 in parallel push-pull would be ok. You can push the screen at 400 volts per other posts I read. Thus 400 volts plate with correct bias. An 807 is a 6L6G with a slightly higher rated plate & screen.
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Old 25th March 2005, 03:28 AM   #8
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6BG6 is also worth a shot. http://www.vacuumtubes.com/6BG6.html
like a 6l6GC or 807 with a different pinout. I'm not sure if triode connected is the right way to go, you could get much more power in ultralinear, but it wouldn't be too hard to add a simple switch to make it selectable triode/pentode/ultra linear. Hammond transformers always have the ultralinear taps. The choice of UL/triode/pentode is really a personal preference, but since you are new to tubes, I would recommend trying to get an output transformer with the UL taps on it so that you have that option.
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