Bad Sounding Plexi

[hogy]

I just got through tuning up a '68 50W Tremolo head that sounded particularly bad.

Despite the fact that this amp had been played extensively over its lifetime, I found that it has never sounded any better since day one. Somebody loved it anyway. :jo

I got a geeky chuckle out of it, have a look:

http://pic18.picturetrail.com/VOL921/489579/5923483/330543511.jpg

[V846]

polarity issue :}

[hasserl]

rK bypass cap backwards?

[hasserl]

So hogy, what's the deal here? Is the issue the reversed biased cathode bypass cap? I always thought that was just a longevity issue, that the cap would fail prematurely if installed the wrong way. I never experimented with mounting them backwards, but isn't the capacitance the same either way? If so, would it really effect the sound? Of course, considering the age of this amp I would say longevity wasn't a problem either.

Or was the issue something else I didn't see?

[Trout]

I got a geeky chuckle out of it, have a look:


Foolishly I will admit that once upon a time I did that exact thing!
Funny how you can stare at them for days on the bench and not notice it, then take a picture, get ready to post a help thread and spot it instantly!

[Blue Strat]

Don't they leak DC when polarized backwards?

[hogy]

Yes, the cathode bypass cap is backwards from the factory. It affected the sound drastically, but, to be honest, I didn't measure to see if it had failed because of that. Simply installed a new one correctly and the amp sounded great.

[hamfist]

40 years of unnecessary poor tone. That's a tragedy !!

[Rosewood]

Even modern insertion machines put them in backwards sometimes.

[David Robrecht]

I ran into the same thing on a mid 50's Gibson GA 40 Les Paul amp. It needed a cap job and some leaking coupling caps replaced. I don't know how much it affected the tone because I did everything at once. So, yes, it does happen.
Dave

[Trout]

Even modern insertion machines put them in backwards sometimes.

:agree


Even modern capacitor manufactures make then backwards occasionally. There were a few posts around a while back with pictures of Sprague Atom caps with the heatshrink polarity/labeling backwards!