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It is currently 20 Jul 2018, 02:02

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PostPosted: 12 Jul 2018, 10:17 
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Joined: 07 Jan 2018, 07:13
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Hello,

Just to be certain, the 2X 100uF caps before the pair of 100R resistors in the P.S. would denote two 100uF caps wired in parallel at this point?

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PostPosted: 12 Jul 2018, 16:56 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, That is correct.

Good listening
Bruce

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PostPosted: 12 Jul 2018, 19:45 
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Hello,

Would someone be able to give me a quick explanation of how this 555 timer works in this circuit? It looks like it might be wired in monostable mode, but wouldn’t the relay turn off after a set duration? I assume that is not the case and that it is an On-delay circuit, I just don’t understand stand it. Also, how is the timing interval calculated and adjusted for the timing duration?

Thank you!


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PostPosted: 12 Jul 2018, 21:43 
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Hi, It is set as a delay. The RC time constant holds the output pin high when the 555 is started. Thus no current flows through the relay coil. At the end of the period (about 75 seconds) the output goes low and stays there until the power if turned off. It could have been done the opposite way with the relay on the ground side but this way is more fail safe. If the heater supply fails the relay can not be activated and there will be no high voltage applied to the capacitors. It is true thought that if the 12 volts supply fails then there is not likely to be any voltage to operate the relay anyhow. Just basically designers choice.

Good listening
Bruce

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PostPosted: 13 Jul 2018, 07:59 
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Hi,

Since the output pin goes high when the 555 is started wouldn’t the relay coil go high as soon as the amp is powered up? If this is the case, Is the B+ supposed to be connected to the N.C. contacts of the relay so that it opens immediately on power up breaking the B+ until the end of the timer duration?

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PostPosted: 13 Jul 2018, 10:09 
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Hi, No. The relay coil is connected to the +12 and is grounded (thus activated) through the 555 when it goes low. The high voltage is interrupted between the rectifiers and the first filter. So while the contacts at the relay have the pulsing DC from the rectifiers on one side, the filter string has nothing. This minimizes the chance of charging the caps with no way to discharge them if there is a failure. When the relay activates it connects the rectifiers to the filters. At this point the tubes are well warmed up and will conduct. If the power is shut off at this point then the tubes will still conduct for a while and drain the voltage off the capacitors. The relay is always activated while the amps are running. Any sort of failure will cause it to shut off and denergize the filter string.

Good listening.

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PostPosted: 18 Jul 2018, 14:28 
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Joined: 18 Jul 2018, 13:16
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hello.
I built an amplifier according to the oddwatt scheme with el84 and ecc82.
I have a problem with low output 1w.
the parameters appear to be alright. anode 220v 6.3v
el84 15v cathode.
  1 anode ecc82 160v 2anoda 80v, cathode 1,8v.
the components are fine, but the amplifier plays weak.
lm317 1,2v out.
I do not know advice, so please advice.
sorry for the bad language.
Thank you


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