GAMPS logo

GAMPS logo


Fender Champ SF modifying to Princeton AA964

I have Fender Champ silverface in my stock. It has been modified already by myself.

MOD = Vibrato circuit was disabled.  Grill cloth was replaced with gold one.
Jpeg of SH Champ front view
SF Champ in my stock, already modified. Front view

MOD = AC Inlet has been added. Speaker Jack has been changed to phone from RCA and relocated on the back panel.
SF Champ rear view 
MOD = CT has been added instead of decoupling resistor 1K ohm 1W.
The power amp stage is still single ended 6V6 though.
One preamp tube has been added for more gain stage.
CT( Choke Transformer ) and a pre tube has been added 

MOD = Removed circuit board.  Wired resistors and capacitors using terminal strips.
Used multiple axial electrolytic capacitors instead of multi section electrolytic.
Circuit has been remounted completely

All  mods were for experimental purposes to determine the sound difference.
And the data was captured. The experiment has been done.

So, it's the time to restore the amplifier.

Restoring back to the original Champ is not so interesting or enjoyable.

I wanted more joy.

Well, PT of the Champ and the Princeton is the same.
The same voltage and the same current value.

So if I replace the OT with one for Pushpull and if I add a US tube socket for another 6V6, I will be able to convert the Champ to Princeton !!! Need the circuit modification too of course.
Parts number and the specification of all the Fender guitar amplifier's transformers
Fender amplifier's transformers
 decided to restore my scratched Champ to Princeton amp.

 Step 1.  Speaker

 When the experiment has been performed Original speaker was replaced with Jensen 8" ceramic.
The picture of cabvinet which mounts Jensen speaker
Original speaker has been replaced with Jensen ceramic

During the experiment, it was replaced with Fender replacement 8" speaker.
  It is probably made by Eminence.
Fender 8" replacement speaker
Then after mounted Fender Replacement speaker 

This time, replaced with the 10" Celestion. Speaker hole is the same as 8", but added extra screw holes for mounting 10 inch speaker.
10 inch celestion has been installed

Step 2.  Transformer and other elements

Removed CT.
Replaced OT from SE Champ to one for PP 17W 8K-8Ohm.
Installed one US tube socket.
Installed electrolytic multisection capacitor (F&T 36microfalad x2 )
Removed extra preamp tube socket

two pictures before and after of Chassiss top view
Chassiss top view difference

Step 3. Circuit Modification

Installed circuit board instead of terminal strips
Reduced electrolytic axial capacitor's quantity by using multi section.
Revived vibrato circuit
Assembled GAMPS original circuit inspired by AA964 Princeton.
Coupling capacitors are Orangedrop film, Murata ceramic and Sizuki film.
Resistors are 1W Ohmiote for power and 1/2W Kamaya carbon composition

Two pictures before and after of the circuit
Circuit view
Step 4. Bias adjust
 Differing from AA964, this amplifier has bias depth adjustment pot.
 Adjusted the pots by refering to 6V6 plate voltage and by measuring 6V6 cathode current.
A little colder setting.
Bias adjust
Step 5. Facade change
Replaced gril cloth with silver one from yellowish one
Speed and Intensity pot returned.
2 pictures. Before and after.
Front view before and after

Step 6. Rear view change
removed AC inlet--- power cord is inserted chassis under
removed speaker phone jack--- RCA speaker jack is located under
added a toggle switch.
This switches pentode mode and ultra lenear mode of OT and power tube operation mode.
Two pictures before and after of rear view
rear view before and after
Step 7. Made original foot switch for vibrato on off.

Made the original foot switch for vibrato on/off.
Box itself is made of  alminum to get lighter weight.
In order to lower the noise, put extra metal, brass and cupper for emphasizing zero volt grounding level of the switch box.
Upper picture is outside view and lower is inside
Vibrato foot switch facade and inside

Step 8. completion

Outer facade is The Fender Vibro Champ silverface and the circuit is modified to Princeton amp.
Front view of the amplifier, foot switch attached.
Front view

Rear view of the amplifier
Rear view

Will post the sound clip of the amplifier soon.

Hope you're going to have the nicest guitar playing life. Thank you.

0 件のコメント: