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Post subject: Making A Vibro Champ heated wires into twisted pairs
Posted: Wed Jul 06, 2011 9:33 pm
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Some photos of making a VC into a twisted pairs of heater. Gotta lift the ground straps off the 6V6GT and 12AX7. The hardest part was taking the lamp outta the amp and unsoldering one tang that is tagged to ground. Then, soldering the two separate heater lines to the lamp.... then running the two separate lines to each tube. Be sure to remove the grounding straps from each tube's heater line tang to ground.

The power transformer I used had a center tap on the heater line. So, there is no need for the terminal 100-ohm resistors to ground. Anyhow, here are some early photos:

Note the double lines to the lamp:

Image

And the twisted pair of heater lines to each tube. And the removed heater grounding straps (with remaining solder blobs):

Image


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Post subject: Re: Making A Vibro Champ heated wires into twisted pairs
Posted: Wed Jul 06, 2011 10:11 pm
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Sweet job, Steve!

Did the mod reduce the hum as anticipated?

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Making A Vibro Champ heated wires into twisted pairs
Posted: Thu Jul 07, 2011 2:06 am
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Arjay,

BIG difference! At least in this BF Vibro-Champ. The usual hum which becomes apparent above "5" is gone. I'd say taking the heater line off the chassis made the amp about as quiet as a well-tuned Deluxe. And I'm using the fairly efficient Weber 8F150 speaker.

Worth the effort in my opinion. Except for having to remove the lamp holder and unsolder one lead. Then, you can rotate the tangs so that they are away from the chassis, the holder support, and each other.

I wired the green 6VAC lines off the PT directly to these lamp tangs. Then, the first extension went to the 6V6GT. Remainder to the 12AX7's.

This PT (Mercury Magnetics) has a center tap line off the heater---so there is no need to use 100-ohm resistors. But if you were to use the stock PT (which has no CT)--- you'd prolly need to put one 100-ohm, 1/2 watt resistor from each lamp connnection to ground. To create an artificial CT.

Only noise I hear (without guitar plugged in) is a faint hiss at "10." Most likely from a tired input tube or dressing around that tube. Barely audible (need to put ear right up against speaker)--- so I'll let sleeping dogs lie.

Amp got new cap can and bypass caps. Plus, new resistors in power supply. One mica cap in the gain stage was replaced with an OD. Tremolo/Vibrato "triplet" micas were replaced with heavier-duty caps.


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Post subject: Re: Making A Vibro Champ heated wires into twisted pairs
Posted: Thu Jul 07, 2011 5:30 am
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You can do the same mods with the stock Power Transformer as BMw2002Ti said. This give you the same low noise amp as if you put a new PT.

I do that many times

But you MUST add two 100 ohms resistor to ground.


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