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Post subject: Warming up my Vibro Champ
Posted: Sat Sep 20, 2014 3:42 am
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Aspiring Musician
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Joined: Fri Jul 13, 2007 12:52 am
Posts: 326
Location: Southern UK
So I have my Weber speaker and I have installed it in the Vibro Champ. When I switched it for the first time and sounded a note, the sound would be muted until the sting vibration reduced and then the volume would come back to normal. It seems OK now.

Q1. Was this the speaker or something else caused by it travels from Italy to the UK.

When I switch on the amp it takes a few moments then produces a quite hum, then there is a loud click and the hum increase to what I presume is normal hummmm.

Q2 Is this correct or does something else need replacing?

Thanks for your interest.


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Post subject: Re: Warming up my Vibro Champ
Posted: Sat Sep 20, 2014 6:58 am
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Try pulling each tube and cleaning pins and sockets with contact cleaner. Work the solution onto the contact surface, by removing and replacing tubes a few times.

Use contact cleaner on input jack, pots, speaker jack, vibrato foot switch jack.

See if that helps. If not, you may need a new main filter capacitor can. I like using this one in the Champs and VC I restore.

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


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Post subject: Re: Warming up my Vibro Champ
Posted: Sat Sep 20, 2014 7:38 am
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Aspiring Musician
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Joined: Fri Jul 13, 2007 12:52 am
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Location: Southern UK
Thanks again! I need to find a long lost cousin who can post items to the UK as a gift :lol:

I thought I would take a peak inside, all looks original>

Image

Image


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Post subject: Re: Warming up my Vibro Champ
Posted: Sat Sep 20, 2014 12:23 pm
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shaky, the cathode resistor on the 6V6GT looks cooked (resistor circled in red). You will get very little output if this resistor and the bypass cap (parallel and next to this resistor) are way out-of-spec.

OEM values for resistor = 470-ohm, 1-watt. For bypass cap = 25mfd/25VDC. I like to use a 5-watt wire wound 470-ohm resistor and a 25mfd/50VDC rated cap. The 5-watt resistor and 50VDC rated cap will have better life under the heated conditions, in the amp.

You should prolly replace the main filter cap can and all other bypass caps (those other 25mfd/25VDC paper caps).

Also, check the values of the 1K-ohm and 10k-ohm, 1 watt resistors that are on the left edge of the circuit board. These are the power rail resistors in the power supply.

See schematic:

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



Good luck! Keep us informed. :mrgreen:

------


Image


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Post subject: Re: Warming up my Vibro Champ
Posted: Sat Sep 20, 2014 1:25 pm
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Location: Province de Québec, Canada
BMW2002Ti wrote:
shaky, the cathode resistor on the 6V6GT looks cooked (resistor circled in red). You will get very little output if this resistor and the bypass cap (parallel and next to this resistor) are way out-of-spec.

OEM values for resistor = 470-ohm, 1-watt. For bypass cap = 25mfd/25VDC. I like to use a 5-watt wire wound 470-ohm resistor and a 25mfd/50VDC rated cap. The 5-watt resistor and 50VDC rated cap will have better life under the heated conditions, in the amp.

You should prolly replace the main filter cap can and all other bypass caps (those other 25mfd/25VDC paper caps).

Also, check the values of the 1K-ohm and 10k-ohm, 1 watt resistors that are on the left edge of the circuit board. These are the power rail resistors in the power supply.

See schematic:

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



Good luck! Keep us informed. :mrgreen:

------


l]


+1 :D


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Post subject: Re: Warming up my Vibro Champ
Posted: Sun Sep 21, 2014 12:41 am
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Aspiring Musician
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Joined: Fri Jul 13, 2007 12:52 am
Posts: 326
Location: Southern UK
Well spotted and thanks, I'm glad I posted the pic now. I'll measure the resistor asap. Now this has fired up another question in my thoughts. When I replace these components, I really want to keep this amp looking fairly original, so I need to source where possible original spec parts. Any ideas? At the same I want to use it as much as possible which is a bit of a contradiction.

So the answer is to build a new one with new improved ingredients! I do love a project. I have a Mallory transformer on the way which I was going to fit in the VC but now seems destined for the project.

Any more recommendations for components and their upgrades? I know nothing about amps but did train in the aircraft industry which leaves me with a raft of redundant skills waiting to be used :?

Something like this but I will buy and build the board.

Image


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Post subject: Re: Warming up my Vibro Champ
Posted: Sun Sep 21, 2014 12:55 am
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All these modern parts are available at tubesandmore.com . I talk about your las post with modern board .


You may need to replace all the "big " brown bypass caps. .I use Mallory 25 MFD 50 volts , cheaper than the 25 volts. You need 3 of those and a one 10 mfd

These are the black caps on the modern board.


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Post subject: Re: Warming up my Vibro Champ
Posted: Sun Sep 21, 2014 7:12 am
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shaky, I'm a bit confused. Is the board (link below) what you are going to put into the VC? Or are you going to use the stock board and just upgrade certain components?

http://www.far-canal.co.uk/loaded_fende ... _vibro.jpg

I would keep the amp as stock as possible. Only replace items that need replacing. Electrolytic caps and cap cans dry out with age. They cease to be effective. You need to replace them. The cap can. And all the paper Mallory bypass caps.

I usually replace the 470-ohm cathode-tied resistor off the 6V6GT. Use one like the photo above. A "sandbox" 5-watt wire-wound one. Set the 25mfd bypass cap away from this resistor, to help keep heat off it. As Stratele said, use 25mfd/50VDC Atoms to replace the OEM ones.

Pull one leg of the 1k-ohm and 10k-ohm resistors in the power rail. Measure for out-of-spec (> 20% tolerance). Replace any out-of-spec ones with nominal value 2-watt metal oxide ones.

After that, plug in good tubes. Test the tone out. This is all you may to do. Don't change coupling caps or other resistors without testing the amp, after 'lytic cap changes.

Report back, on the tone of the amp after these changes. Good luck! :D


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Post subject: Re: Warming up my Vibro Champ
Posted: Sun Sep 21, 2014 9:36 am
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Aspiring Musician
Aspiring Musician

Joined: Fri Jul 13, 2007 12:52 am
Posts: 326
Location: Southern UK
I do confuse people some times sorry :?

I am going to do as little as possible to the '66 VC (but fix it up) and then build another amp, maybe even go for a VC head and speaker, to use frequently.

Thanks for all the help, I will obviously need a few more answers as time goes by.


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