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Post subject: Fender Vibro Champ trouble.
Posted: Sat Nov 15, 2014 7:12 am
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Hi Fender-fellas!
A few months ago I bought a 1966 Vibro Champ on ebay. My first blackface amp, and I've been so happy with it. Very warm sounding.
But recently it started to sound harsh and thin, with a lower output. Thought it was the old Oxford speaker, and replaced it with a new Jensen P8R - with no improvement.
The fuse seems intact to me. If you have the time ... what would be your next step in troubleshooting? Tubes, caps?

https://www.youtube.com/watch?v=7KK1loBLMyY
Kind regards, Kenneth/Copenhagen.


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Sat Nov 15, 2014 8:41 am
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Welcome to the Forum! Very nice amp. :D :thumpsup:

Sounds like the cathode-tied 470-ohm, 1-watt resistor and/or 25mfd/25VDC bypass cap on the 6V6GT output tube maybe out-of-spec. Prolly all four bypass caps and the main filter cap can should be replaced. They could be the original components.

Can you do simple circuit work? Remember to unplug and discharge main filer cap can, before working on any amp.


I would use:

1.) Sprague ATOM 25mfd/50VDC rated bypass caps.

2.) Any good 470ohm, 2-watt metal oxide resistor for cathode-to-ground on the 6V6GT.

3.) CE 20/20/20 at 525VDC cap can.


Schematic:

http://bmamps.com/Schematics/fender/cha ... _schem.pdf


Cap Can:

https://www.tubesandmore.com/products/C-EC20X3-525


25/50 bypass caps:

https://www.tubesandmore.com/products/c ... gue%20Atom


Good luck! Keep us posted.


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Sat Nov 15, 2014 8:59 am
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Photos of before and after.

1.) Vibro-Champ with original components. The white caps are OEM Mallory. One bypass had already been replaced by a new Sprague ATOM (black with green lettering). Cap can connections are to the left of the circuit board. Three wires to the square, triangle, semi-circle labeled tangs.


Image


2.) After photo of a Bronco Amp. Essentially a Vibro-Champ with silverface control panel and red lettering. Some bypass caps have been changed-out. The bypass cap off the 6V6GT is an F&T (33mfd/160VDC). The OEM 10mfd/25VDC has been replaced by an 8mfd/150VDC cap.


Image


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Sat Nov 15, 2014 1:05 pm
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BMW2002Ti wrote:
Welcome to the Forum! Very nice amp. :D :thumpsup:

Sounds like the cathode-tied 470-ohm, 1-watt resistor and/or 25mfd/25VDC bypass cap on the 6V6GT output tube maybe out-of-spec. Prolly all four bypass caps and the main filter cap can should be replaced. They could be the original components.

Can you do simple circuit work? Remember to unplug and discharge main filer cap can, before working on any amp.


I would use:

1.) Sprague ATOM 25mfd/50VDC rated bypass caps.

2.) Any good 470ohm, 2-watt metal oxide resistor for cathode-to-ground on the 6V6GT.

3.) CE 20/20/20 at 525VDC cap can.


Schematic:

http://bmamps.com/Schematics/fender/cha ... _schem.pdf


Cap Can:

https://www.tubesandmore.com/products/C-EC20X3-525


25/50 bypass caps:




Good luck! Keep us posted.


+1

There is a good example of a cooked cathode resistor in this post from shaky a couple of months ago:

viewtopic.php?f=12&t=95966

You'll need a heavy duty soldering iron for soldering the tabs on the cap can to the chassis.

vinyl


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Sat Nov 15, 2014 3:32 pm
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Location: Gateway to the West
Nice Diagnosis Dr. Beemer! OP...we need pics too!

:mrgreen:

T2

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Post subject: Re: Fender Vibro Champ trouble.
Posted: Sun Nov 16, 2014 1:13 pm
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Hi there guys!

Thanks for your quick and detailed responses, pictures and all ...
I've had the caps under suspicion because of the way the amp reacted - with a sudden volume-drop and loss of tone. Like something burned out. It didn't happen over a period of time. But maybe changing the tubes could make a difference too (?).

No .... I haven't done much soldering - besides from my instrument- and other cables.
Because of the many options according to components, resistors etc.... (which I don't know much of - yet), I might leave it to a professional this time. The amp is a keeper for sure. And hopefully will be joined by a Princeton sooner or later.

I'll report back about it ... yes! And thanks for the links ... cool schematics !

Regards - Kenneth.


Last edited by Kenneth Hermansen on Sun Nov 16, 2014 1:26 pm, edited 1 time in total.

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Post subject: Re: Fender Vibro Champ trouble.
Posted: Sun Nov 16, 2014 1:22 pm
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Kenneth, best to find a good amp tech to recap your amp. You are prolly correct about the bypass caps. When they fail, you lose a lot of bass and transients become weak. Where do you live?

Have the can, all bypass caps, and the cathode-to-ground 820-ohm resistor changed. Your amp should come back to life.

BTW... if you get a new 6V6GT, you won't need to bias it. The amp is a cathode-biased, single-ended. Should self-level wrt to the new tube. A new 12AX7 input tube may also give life back to the amp. I like the Gold Lion ECC83/12AX7 (Russian made) for this amp.


http://www.amazon.com/Genalex-Gold-Lion ... lion+ecc83


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Sun Nov 16, 2014 3:04 pm
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We have a very qualified amp-tech in Copenhagen - where I live (there's more than one of course).
I'm sure he knows what to do. But ... well yeah, I could do a little more homework, before handing it over ...
Busy week upcoming, but I'll see if I can get some pics from the components.
Caps, can and cathode-resistor is to be studied ... :)
Some fine tubes. They aren't New Old Stock, are they?

Regards - Kenneth


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Sun Nov 16, 2014 5:05 pm
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The Genalex/Gold Lion are current Russian made tubes. Their new ECC83/12AX7 have as close a tone to the original RCA 7025, that I've found for new tubes. Original 1960's British made NOS GEC/MOV ECC83 (B759) Gold Lion tubes are near unobtanium. :mrgreen: :!: :mrgreen:

http://www.ebay.com/itm/1-HOLY-GRAIL-GE ... 3cec6255c3


As for 6V6GT's... I'd opt for a good NOS 6V6GTA or GTY. Like this CBS-Hytron mil spec, black plate 6V6GTY.


http://www.ebay.com/itm/NOS-CBS-Hytron- ... 23439fb9ee


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Mon Dec 01, 2014 4:49 pm
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Hi again!

Just had the Vibro Champ back from the local amp-shaman.
Much better now. It had some resistors changed. Think I will look for some NOS tubes also.
Maybe from your links.

It has become a little louder after the repair, and sounds somehow more present/new/energetic.

Like this (sleepy late-night playing though):
https://www.youtube.com/watch?v=GBiZPhG ... Q181sd9sIQ

Thanks again. And I imagine I will get to know more of the inside of amps, since it's not my last blackface amp :)
Regards - Kenneth


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Mon Dec 01, 2014 6:17 pm
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Very nice! And thanks, for posting your follow-up. That helps complete the thread. :) :)

You may want to think about an aftermarket speaker. To get more efficient output form the 5-watt amp.

I like the Weber Vintage 8F150. Nice, tight bass. Clean mids & highs. Very efficient.

https://taweber.powweb.com/weber/8f150.htm

-----

Back of my BFVC with Weber 8F150:


Image


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Mon Dec 01, 2014 7:02 pm
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Sure, I will research on the weber speaker.
To me, the Jensen alnico's sounds natural, vintage, un-compressed. I just installed a P8R ... and it's okay for now ..... but still sounds ... new .. though.
Could be a good idea having a few others home - for AB testing.
Thanks again! And nice shot!
Ken.


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Wed Dec 03, 2014 10:06 pm
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yeah ... well .... it seems the amp still has a lack of bottom-end. Got worse during the day.
Going for new tubes now!


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Post subject: Re: Fender Vibro Champ trouble.
Posted: Wed Dec 03, 2014 10:37 pm
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Go for good US made NOS if you can. 6V6GTA for clean high notes. 6V6GTY for good bass and mids.


http://www.ebay.com/sch/i.html?_from=R4 ... a&_sacat=0

http://www.ebay.com/sch/i.html?_odkw=6v ... y&_sacat=0


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