Fender tube amps from the 1990s and 2000s.

[laurie]

What you see above is the correct engineering solution for the amount of heat this arrangement generates. Fender simply did not do it. My guess is that their factory arrangement would last well past the warranty expiry, so "good enough".

As an engineer, I find this to be galling - financial expediency. <bah>

[laurie]

This is now the front of the PCB.
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Hot Rod3.jpg (275.04 KiB) Viewed 3100 times

[Pepe]

Excellent upgrade!

[laurie]

What you see above is the correct engineering solution for the amount of heat this arrangement generates. Fender simply did not do it. My guess is that their factory arrangement would last well past the warranty expiry, so "good enough".

As an engineer, I find this to be galling - financial expediency. <bah>

I'm still annoyed when I think about what I had to do to fix this amp.

What it actually needs is an additional output winding on the transformer ... 15-0-15 or something, full-wave rectified into +/-20VDC then through proper voltage regulators (e.g. 7815/7915). That would add maybe $10 (or less) to the cost.

Using the single 39VAC winding that generates the tube bias and half-wave rectifying it to +/-48VDC is cheap, lazy, and nasty engineering. Standard voltage regulators can't withstand 48V input, so the only "easy" option the designers had was to use Zeners which are inefficient, noisy, and the dropper resistors generate a lot of heat.