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Post subject: Everything Old is Older Again... ('72 Champ Redux)
Posted: Mon Jun 26, 2017 2:16 pm
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As I mentioned a while ago, I had plans for my 72 champ I was refreshing. So here it is, FINALLY!

Custom cabinet finished in tweed w/ brown grille cloth, housing a custom ordered Ted Weber 12", 15watt 3.2 ohm speaker. The cabinet is about 18" high x 9" deep at the bottom.

This cabinet, built by Armadillo Amp Works, is freaking beautiful!

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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Mon Jun 26, 2017 3:12 pm
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Very nice , congrat.


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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Mon Jun 26, 2017 3:18 pm
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That conversion cries out for a blackface front panel.

Really really nice!

Arjay

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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Mon Jun 26, 2017 3:21 pm
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Retroverbial wrote:
That conversion cries out for a blackface front panel.

Really really nice!

Arjay


Yeah, but I haven't quite figured out where to lay my hands on one...


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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Mon Jun 26, 2017 4:37 pm
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Ebay often has a good selection of repro and original face plates.

Arjay

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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Mon Jun 26, 2017 7:25 pm
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With the crackdown on "unlicensed" repro's, it's gotten tougher to find such things. The only one I found was $90... Not sure I want it that bad.

I'm contemplating playing around with the tone stack to see if I can coax a little more bottom end out of the amp now with this 12" speaker...


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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Mon Jun 26, 2017 9:23 pm
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There is a mod that reverts the BF and SF Champ circuit back to a 5F1 type circuit. That has no adjustable tone stack. Lower global negative feedback. Less plate voltages on the 12AX7 input/gain stage tube.

Returns the amp back to warmer midrange, esp at lower volumes and better OD tone when cranked to "10."

http://www.electronicstudio.net/schemat ... _schem.pdf

http://ampwares.com/schematics/champ_5f1.pdf

Following mods are to revert the Vibro-Champ back to 5F1-like circuit, but keep the vibrato/tremolo. Steps and reasons are similar, for the BF and SF Champ.

" To bypass the tone control, you are going to replace is the 250 pico-farad cap off pin 1 of the first 12AX7. Take the right hand wire off the VOLUME control (tape it). Take the right hand lead off the TREBLE Control. Solder the right hand lead from the TREBLE pot onto the VOLUME control.

On the first 12AX7 you’ll see this 250 pico-farad cap connected, in a vee-pattern, to two 100K-ohm resistors. Remove the 250 pico-farad cap and replace it with a 0.022 mfd/600 VDC coupling cap (Orange Drop 716P or Mallory-150 is fine). Remove the 100k-ohm resistor that lies horizontal on the circuit board. At the bottom right of the circuit board.

You now have the tone pots bypassed. Which will give the amp much better midrange, as the tone pot arrangement robs the amp of inherent great 6V6GT mids.

To change the feedback loop to tweed standard, find the 2700-ohm resistor running from the speaker connection wire. Replace this resistor with a 22k-ohm, ½ watt resistor. Solder it DIRECTLY to pin 8 of the 12AX7 (eyelet just to the right of the speaker lead).

The silver faced Vibro Champ runs the 12AX7 too high voltage, which give a strident voice to the amp. Drop it back to tweed standards by replacing the 10K-ohm, 2 watt resistor with a 22k-ohm, 2 watt resistor.

The resistor is between the second and third filter cap on the circuit board. Now, the voltage on the plate is back down to black face standards. If the GAIN is still a bit too much, you can remove the bypass cap on the first 12AX7 (far right 25mfd/25 VDC electrolytic cap on the board). . This tube did not have a bypass cap, on the original tweed Champs.

Last thing I did with my Vibro Champ is get a good speaker. I chose a Vintage 8-inch from Weber Speakers. Any good 8-inch, for the cab or a 12-inch for an external cab will be better than the cheap 8-inch Fender put into their Vibro Champ.

I’ve personally had very good success changing the 5Y3GT rectifier for a 6087. Gives better bass and maintains the nice brown midrange. "


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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Mon Jun 26, 2017 10:16 pm
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He's already upgraded the speaker to a pretty fine Weber alnico twelve.

Arjay

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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Mon Jun 26, 2017 11:19 pm
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Retroverbial wrote:
He's already upgraded the speaker to a pretty fine Weber alnico twelve.

Arjay


Oh yeah... failed Reading Comprehension 101, again. :lol: Great speaker!

BTW... the 5F1 mods can be taken in parts or whole. This maybe better summary:

1.) Bypass the tone control, you are going to replace is the 250 pico-farad cap off pin 1 of the first 12AX7. Take the right-hand wire off the VOLUME control (tape it). Take the right-hand lead off the TREBLE Control. Solder the right-hand lead from the TREBLE pot onto the VOLUME control.

On the first 12AX7 you’ll see a 250 pico-farad cap connected, in a vee-pattern, to two 100K-ohm resistors. Remove the 250 pico-farad cap and replace it with a 0.022 mfd/600 VDC coupling cap (Orange Drop 716P or Mallory-150 is fine). Remove the 100k-ohm resistor that lies horizontal on the circuit board. At the bottom, right of the circuit board.

You now have the tone pots bypassed. Which will give the amp much better midrange, as the tone pot arrangement robs the amp of inherent great 6V6GT midrange.

2.) To change the feedback loop to tweed standard, find the 2700-ohm resistor running from the speaker connection wire. Replace this resistor with a 22k-ohm, ½ watt resistor. Solder it DIRECTLY to pin 8 of the 12AX7 (eyelet just to the right of the speaker lead). NOT to the resistor (1500/47) voltage divide point.

3.) The BF and SF Champ & Vibro-Champ runs the 12AX7 too high voltage, which give a strident voice to the amp. Drop it back to tweed standards by replacing the 10K-ohm, 2-watt resistor, in the PSU power rail --- with a 22k-ohm, 2-watt resistor.

The resistor is between the second and third filter cap on the circuit board. Now, the voltage on the plate is back down to black face standards.

4.) If the GAIN or OD is still a bit too much, you can remove the bypass cap on the first 12AX7 (far right 25mfd/25 VDC electrolytic cap on the board). This tube did not have a bypass cap, on the original 5F1 tweed Champs.

5.) Last thing I did with my Vibro-Champ is get a good speaker. I chose a Vintage 8-inch from Weber Speakers. Any good 8-inch, for the cab or a 12-inch for an external cab will be better than the cheap 8-inch Fender put into their Vibro-Champ.

6.) I’ve personally had very good success changing the 5Y3GT rectifier for a 6087. Gives better bass and maintains the nice brown midrange. It has a slow start-up, like the GZ34/5AR4, too.


Photo with circuit mods, in place. BF Vibro Champ.

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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Tue Jun 27, 2017 5:38 am
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7chord wrote:
As I mentioned a while ago, I had plans for my 72 champ I was refreshing. So here it is, FINALLY!

Custom cabinet finished in tweed w/ brown grille cloth, housing a custom ordered Ted Weber 12", 15watt 3.2 ohm speaker. The cabinet is about 18" high x 9" deep at the bottom.

This cabinet, built by Armadillo Amp Works, is freaking beautiful!


Can't say enough good things about Will at Armadillo Amp Works... he provided the repro cabinet for my 1962 Vibrolux. That Champ looks awesome.


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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Tue Jun 27, 2017 12:15 pm
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Some interesting ideas, but I'm going to stew on them a while and give the speaker a chance to break in before I can really decide to go ahead and mod it.


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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Wed Jun 28, 2017 6:12 pm
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7chord wrote:
With the crackdown on "unlicensed" repro's, it's gotten tougher to find such things. The only one I found was $90... Not sure I want it that bad.

I'm contemplating playing around with the tone stack to see if I can coax a little more bottom end out of the amp now with this 12" speaker...


$90 is about right, that is about what I paid when I did the refurb on a '69 Super Reverb Black Face front plate. It was also excellent quality, something to seriously consider. Either way, a great looking job, once the speaker is broken in that thing ought to scream!

T2

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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Wed Jun 28, 2017 6:22 pm
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T2Stratman wrote:
$90 is about right, that is about what I paid when I did the refurb on a '69 Super Reverb Black Face front plate.


+1

This is a dollar-intensive hobby (*very* intensive). Those with shallow pockets should take up skateboarding or miniature golf.

:wink:

Arjay

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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Wed Jun 28, 2017 10:08 pm
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Retroverbial wrote:
T2Stratman wrote:
$90 is about right, that is about what I paid when I did the refurb on a '69 Super Reverb Black Face front plate.


+1

This is a dollar-intensive hobby (*very* intensive). Those with shallow pockets should take up skateboarding or miniature golf.

:wink:

Arjay


Yeah, yeah - I know. I already ordered the FP... If it's worth doing, it's worth over doing... You lot are a bunch of enablers... :roll:


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Post subject: Re: Everything Old is Older Again... ('72 Champ Redux)
Posted: Wed Jun 28, 2017 10:13 pm
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7chord wrote:
You lot are a bunch of enablers... :roll:


We're just here to help.

:mrgreen:

Arjay

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