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Post subject: Champ with a Zener?
Posted: Mon Aug 14, 2017 11:33 pm
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Location: South Texas
I'm ready to try something I read elsewhere on the web about replacing the resistors on the CT of the PT with zener diodes to drop the volts a little. My wall voltage is 126 AC and the B+ is 392 VDC, which works but would be closer to spec if my AC wasn't so darned hot.

What will I gain or lose in the tone doing this? Also, is there something else to it or is it really as simple as it sounds?

I haven't seen any pics but from what I understand about the mod it's as simple as removing the resistors and using a combination of 5W zener diodes at 11V each in series to ground to lower my B+ voltage. Also read that a 1mf cap may be soldered to the zener and chassis to reduce hum if needed. This sounds easy to do and easy to reverse if needed, but my analytical mind questions why, if it provides some useful purpose, isn't everyone doing it?

Oh yea... just to clarify, it's not a vintage Champ. It's a 5F2A that I pounded out last year with the help of this forum but the process should be the same.

Here it is. I originally planned to just build a head but kept going. That's a Squire Pro-Tone with 63 RI pups next to it. I'm crazy about that guitar, more so than my American.
Thanks again Beemer for the help.

Image
upload the pictures

Thoughts?

Many thanks!
Randy


Last edited by Randy70065 on Mon Aug 14, 2017 11:55 pm, edited 1 time in total.

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Post subject: Re: Champ with a Zener?
Posted: Mon Aug 14, 2017 11:47 pm
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Instead of modifying your Champ, maybe think about building a bucking transformer. Then, you can use it on other amps. Here's a nice DIY...

Image

https://robrobinette.com/5e3_Modificati ... ransformer

It's about 7/8th the way down Rob's great 5A3 page. He also has the diode method to drop b+.

Image

His 5A3 site:

https://robrobinette.com/5e3_Modificati ... ifications


Last edited by BMW2002Ti on Tue Aug 15, 2017 2:16 am, edited 2 times in total.

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Post subject: Re: Champ with a Zener?
Posted: Mon Aug 14, 2017 11:58 pm
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BMW2002Ti wrote:
Instead of modifying your Champ, maybe think about building a bucking transformer. Then, you can use it on other amps. Here's a nice DIY...

https://robrobinette.com/5e3_Modificati ... ransformer


Damn, Beemer. You get less sleep than I do. :-)

Thanks for the link. It looks more involved (fun). I'll give it a read.


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Post subject: Re: Champ with a Zener?
Posted: Tue Aug 15, 2017 12:57 am
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I do zener diodes mod to few ( vintage and modern amp ) amps to drop the B + voltage as specs, sound is better or same in all case.
I never heard about about a 1 mfd cap mod, I have no hum with zener.

viewtopic.php?f=12&t=98981&p=1119431&hilit=zener+diodes#p1119431


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Post subject: Re: Champ with a Zener?
Posted: Tue Aug 15, 2017 4:01 am
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Joined: Tue Nov 27, 2012 6:56 am
Posts: 1677
Location: Coastal Bend, Tx.
If you want a little more flexibility and/or have more than one vintage amplifier perhaps one of these will be worth your money. They offer a smaller "brownie" model as well.
https://www.sweetwater.com/store/detail/BrownBox
Here's my review, fwiw.
Eric
from South Texas
January 25, 2017
Music Background:
Expert Listener/Novice Tech/Novice Player

Big "Brown Box" Sound
A great tool for anyone playing a vintage amp on a regular basis.
Sure you can have a tech. swap components to allow a vintage amplifier to operate at today's higher voltages safely but altering the input voltage is the best place to start.
My B+ went to an A+.
It helped smooth out my TV Deluxe's transition to distortion, lowered the circuit operating voltages and gives me piece of mind wherever I plug in.
Its easy to operate.
The only reason I didn't give it 5*, is because mine shipped w/ a power cord that wasn't as good as it should have been.
Sweetwater Tech Support fixed this minor issue really quick, Thanks.


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Post subject: Re: Champ with a Zener?
Posted: Tue Aug 15, 2017 4:17 am
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sfceric64 wrote:
If you want a little more flexibility and/or have more than one vintage amplifier perhaps one of these will be worth your money. They offer a smaller "brownie" model as well.
https://www.sweetwater.com/store/detail/BrownBox
.



Look great accessoiries :)


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