Tube Replacement (cont.)
Input and Driver Tubes
The input and driver tubes in your Stereo 80 could provide 5,000 to 10,000 hours of use. They will
probably outlast the output tubes by a factor of 2:1. We recommend that the input and driver tubes be
replaced after no more than 3,000 to 4,000 hours of use to avoid the slightly "muffled" sound or slight
bass "roll-off" which can begin to occur with old tubes. This replacement interval is equivalent to about 2
1/2 years when the amplifier is used 4 hours per day (or 5 years when used 2 hours per day).
The most likely source of tube noise in the Stereo 80 is the 12AT7 input tube - V1 (left channel) or V5
(right channel).
Output Tubes
You should expect the EL34s in the Stereo 80 to provide 3,000 to 4,000 hours of use before they have to
be replaced. Some audiophiles replace them after as little as 1000 hours of use to keep the amplifier in
top form. It is not uncommon, however, for an output tube to become faulty during its normal lifetime.
The following conditions indicate possible output tube failure:
➣ An output tube will not bias properly - or refuses to hold its setting.
➣ The amplifier produces a somewhat “muffled” sound during use.
➣ The line fuse blows (other than from normal fuse fatigue).
➣ An output tube glows red during operation.
➣ Arcing is noticed inside the tube, upon close inspection.
➣ A tube filament will not light up.
Maximum performance of the Stereo 80 is achieved by using matched pairs of output tubes. The
amplifier will work without matched output tube pairs, but may not fully meet all of the performance
specifications. Matched pairs of output tubes are available from Dynaco or through your dealer.
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