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Old 14th January 2012, 02:16 AM   #11
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Quote:
Originally Posted by DF96 View Post
OK, each to their own!
Actually reminded me why I bought some 25L6's. Looking at my tube stash and could not remember why I bought these as I had a different tube but running a different heater voltage that could do the same function. Now I remember I wanted to run them off a 24v transformer and double the voltage running the plates around 60v. Or was it triple the voltage and run 90v?
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Old 14th January 2012, 07:45 AM   #12
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EL504 will not work as you expect with Vg2=24V. You should not be able to bias the tube over a few mA.

ECC82 is not the best tube at normal Ua. At this Ua it will perform really bad and will not be able to drive an output tube.
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Old 14th January 2012, 09:18 AM   #13
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by revintage View Post
EL504 will not work as you expect with Vg2=24V. You should not be able to bias the tube over a few mA.

ECC82 is not the best tube at normal Ua. At this Ua it will perform really bad and will not be able to drive an output tube.
Try this amp and you will be surprised.

The PL504 in this circuit is biased at about 35 mA and it is enough.
ECC 82 is frequently used with supply voltage as low as 12Vcc in regenerative radios or small preamps, but for this specific circuit 12FQ7 works better.

Last edited by pilovis; 14th January 2012 at 09:22 AM.
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Old 14th January 2012, 09:31 AM   #14
pilovis is offline pilovis  Italy
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Originally Posted by gcwills View Post
Any photos of your amp Pilovis?
At the moment the amp is just a working wired prototipe, as soon as I put it on a printed circuit board in a decent manner, I will post the photos.
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Old 14th January 2012, 09:31 AM   #15
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Hey, do your math and explain where you got 1W Pout from. 0,1W is probably more true.
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Old 14th January 2012, 09:32 AM   #16
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by revintage View Post
Hey, do your math and explain where you got 1W Pout from. 0,1W is probably more true.
Again, try it and see
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Old 14th January 2012, 09:41 AM   #17
pilovis is offline pilovis  Italy
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I didn't measure the ouput power and can't say this amp is 1 W RMS or 1W PEP or wathever else.
I can just say I use this amp to drive a couple of Sony speaker boxes of 8ohm impedance and the output sound power is enough to sonorize my studio.
For sure it is not 0,1 W othervise it would not been able to drive anything.

The scope of this amp is not to demonstrate to anyone that I made a perfect amp or create a new fantastic project, it is just to listen to my preferred music coming from my laptop at good fidelity and at enough sound level to drive a couple of mini hi-fi boxes without risking electrical shocks.

If you you want to build and try it you are welcome.

Last edited by pilovis; 14th January 2012 at 09:50 AM.
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Old 14th January 2012, 09:52 AM   #18
jane is offline jane  Norway
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Quote:
Originally Posted by pilovis View Post
The PL504 in this circuit is biased at about 35 mA and it is enough.
Max theoretical class A output power depends on the quiescent current (Iq) and the reflected load of the transformer (Rl).
Iq=35mA and Rl=600 ohm should give about 0.37 watt.
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Old 14th January 2012, 09:54 AM   #19
pilovis is offline pilovis  Italy
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This is the first prototype I made (just one channel), after that i built the wired stereo prototype you can see on the schematic above.

Click the image to open in full size.

The first prototype had a bypass catode capacitor on triodes, I removed it to decrease gain and distortion.
The first prototipe had higher bias current on PL504, I decreased it to improve distortion (less output power).

First prototype schematic:

Click the image to open in full size.

Last edited by pilovis; 14th January 2012 at 10:20 AM.
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Old 14th January 2012, 10:32 AM   #20
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Thanks for sharing. Love ideas outside the box.
JimG
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