Question about Audio & Video Receivers
You can get a circuit diagram from here.
The 12ax7's will not glow as bright as the EL34's . Is just the nature of the tubes. The latter being higher powered and the 12ax7 low power. The EL84's as output tubes will always glow brighter, and often even with a dull blue glow about the plates from the higher voltages made available to them. If the plates them selves are glowing red(inside the EL34's). then you have a bias problem. Be careful running the amp in this condition. Do some static checks with the amp off looking for failed components about the bias and screen control stages. .
Start by checking all the DC voltages first. The circuit diagram i supplied the link for has voltages marked for you to check. A common problem with this amp is the 390 ohm 5 watt resistor going open. A faulty output tube(s) may also have caused this. I would replace the output tubes anyways for a good repair.
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Posted on May 29, 2008
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