Fender Bassbreaker 15 is blowing EL84 power tubes

This Fender amp sounds great at this price point, but servicing is not for the faint of heart. To access components is very unfriendly for repair Techs (read “expensive” for owners). This amp had a fault where both EL84 power tubes were fried, with one tube falling apart on removal. Join me as we track down the cause and find a cost-effective solution for this owner. Along the way, you may gain a better understanding of how Cathode Biasing works, and how you can diagnose and correct problems in this part of a cathode biased amp, also seen in many Vox, Dr Z, Matchless and the Marshall 1974 18w (video coming soon).

Index
00:00  Introduction
01:16  The problem is clear, but is the solution?
03:40  Dangerously high plate current
04:15  An explanation of Cathode Biasing
07:50  The schematic reveals possible causes
09:23  Guitar Amp Tech whines repeatedly about modern construction practices
11:35  The fault is found, more swearing ensues
12:05  An economical workaround to the problem and explanation for the Zener Diode in the Cathode bias
16:00  Success. New tubes and the Bassbreaker biases perfectly
17:08  Conclusion and audition of the repaired amp

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• #music
• #amp_makes_loud_noise
• #tubes_red_plating
• #tubes_go_white
• #fender_bassbreaker
• #how_does_cathode_bias_work
• #why_is_there_a_zener_in_the_cathode_bias