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Old 6th December 2003, 01:59 AM   #1
Lico is offline Lico  United States
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Default i finished my first amp

well it's finally finished and working!
looks good, sounds good, i'd have to say i'm pretty glad i did this. i have a question though, can i plug two amps into 1 pair of speakers. of course i'll use only one amp at a time, but will it hurt anything to have them both connected? also, i was wondering if you guys could tell me how to calculate the wattage i'm using. i want to make sure i'm not running the 6v6 to high. thanks
Andy
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Old 6th December 2003, 02:50 AM   #2
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Well without knowing any better, and wanting to compare 2 amps, i hooked up a tube amp and a solid state RS receiver to a set of speakers. It wiped out the solid state receiver...
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Old 6th December 2003, 02:58 AM   #3
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Default Info.

Hi Andy,
"can i plug two amps into 1 pair of speakers. of course i'll use only one amp at a time, but will it hurt anything to have them both connected? also, i was wondering if you guys could tell me how to calculate the wattage i'm using. i want to make sure i'm not running the 6v6 to high. thanks
Andy"

Connecting two amps in and only running one will cause problems. I would suggest not doing it. Power will be lost thru the amp not on and frequency response will probably change.

To get a general idea of the power out, I would connect a signal generator, set to say 1khz, and the output of the amp to a calibrated scope and measure the peak to peak voltage just before clipping.
Divide this voltage by 2.82 to arrive at RMS voltage. Then divide the RMS voltage by the load resistance, resistor and then multiply by the RMS voltage. This should give a general idea of the RMS power output. It should be within 10% accurate I should think.

Take care. Hope this helps.
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Old 6th December 2003, 10:42 AM   #4
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Anytime you are going to use more than one set of amplifiers with one pair of speakers you will need to employ a switcher. I have seen too many instances of damaged amplifiers because of this. A switcher is cheap insurance to guard your investment.


Joe
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Old 6th December 2003, 10:51 AM   #5
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I'm going to guess that you are running the tube too hard. Check the voltage across your bias resistor which I believe is a 255 ohm. I'm going to guess (thanks to tube cad SE) that you have around 13volts or roughly about 52mA of current. I believe this might be too much bias and your plate voltage might be a touch too high.

I think your output in watts RMS will be around 6 into an 8 ohm load.


Joe
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Old 6th December 2003, 04:23 PM   #6
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Datasheet that I looked at showed 5.5 watts in pentode mode. Triode mode would be quite a bit less.

A rule of thumb: triode power out is about 1/4 of plate dissipation--that's max. I think you would not be getting more than 3 watts out and maybe much less--say 2.

But, best way is measure it or draw up the loadlines in triode mode and calculate. The procedure is shown in a tube handbook or designer handbook.

Happy listening and congratulations!
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Old 6th December 2003, 07:10 PM   #7
Lico is offline Lico  United States
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actually, i wanted to know how to calculate the plate dissipation. i don't really care about output power. thanks for telling me about using 2 amps
thanks
andy
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Old 7th December 2003, 01:18 AM   #8
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Default Oh, that's different

I'm a beginner at this but I think you need to determine the current flowing through the tube. Get the voltage drop across the cathode bias resistor and use Ohm's Law to get the current. Next, measure the voltage across the tube. Now you have P=IV or power=current X voltage (power in watts, voltage in volts and current in amps).

If you drew the loadlines on the triode curves, then the first thing that I do is plot the plate dissipation curve to ensure that I don't exceed it when I select operating point. This is another way of seeing the plate dissipation relative to your op point.

Hope I got it right and answered your question!
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Old 7th December 2003, 07:17 PM   #9
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Lico, just curious, what software did you use to draw your circuit diagram? I'm looking for something free and uncomplicated. Doesn't need to do PCB layout or circuit simulation. By the way, most 6V6 single ended circuits I've seen only use about 250v B+.
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Old 8th December 2003, 02:41 PM   #10
Lico is offline Lico  United States
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i didn't draw it actually, i just changed some values on a circuit off the internet and drew in a cap. actually my voltages are all screwed up. i thought i had 300v, but it's actually only 200v. after i get some more power resisters, i'm going to get them as close to 350v for the 6sn7 and 250v for the 6v6 as i can, which is what i really wanted.
andy
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