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FDP Forum / Fender Amps: Vintage (before 1985) / vibrolux no heater center tap



Jun 9th, 2018 10:14 PM   Edit   Profile  

Hi Everyone, my first post.... I'm looking at 63 my vibrolux and notice I have two 100 ohm resitors near the pilot light going to ground. I know this is for hum control via the heaters. My question is this? How common is this in a fender amp? Original or non-original? I've looked under the hood of many vintage fender amps and mine is the only one I've seen with these two 100 ohm buggers in it. It's not it any fender schematics. Thank you.

Moderator Emeritus
(with many stars)

NW Pennsylvania

Jun 9th, 2018 10:20 PM   Edit   Profile  


All the geniuses are either at a gig or sound asleep right now, so be patient and check back in the morning.

In the meantime, it's on this schematic.

Contributing Member

Ooo that sandwich

is gonna get et
Jun 9th, 2018 11:17 PM   Edit   Profile  

They are on the schematic.

In Pinetree's linked schematic, look in the lower right corner, to the right of "Instruments."



Jun 10th, 2018 08:41 AM   Edit   Profile  

well looky there! Thanks y'all. Still, seems kinda odd or rare. I'm gonna have to go thru my schematic book and see if there's any others. I wonder why this particular model dropped the ct, or was it just a supply buyer snafu? Anyways, thank you very much!

Contributing Member

Ooo that sandwich

is gonna get et
Jun 10th, 2018 08:46 AM   Edit   Profile  

Welcome to the FDP!

Contributing Member

So. Cal. USA

Jun 11th, 2018 06:06 PM   Edit   Profile  

Most of the older amps were designed this way. It's a great way to ground reference the heaters and they will act like fuses and go poof in some filament shorts.

It's a good thing and can save a PT.

There is a thread about this in the amp repair section I believe. Worth a read.


Lawndale CA

No Chops but Great Tone ©
Sep 7th, 2018 10:08 PM   Edit   Profile  

The center tapped power transformer is slightly more expensive and resistors were cheap. It was simply a cost decision since functionally either method is fine.

An even better system is a separate small DC transformer and running the filaments on DC voltage. It works fine, doesn't require the tight wire twisting and unusual lead dress, and isn't prone to the hum caused by AC filament wires running near high-voltage DC and transformers.

Bu tit's more expensive. I've only seen it done in a few boutique and one-off builds.

FDP Forum / Fender Amps: Vintage (before 1985) / vibrolux no heater center tap

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