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82 SF Champ revamp
Hi!
I recently purchased an '82 Silverface Fender Champ. I like champs/vibrochamps, and this
one sounds pretty good, but there are a few issues I want to address.
I am new to amp modification and repair, so I want to go through everything I am planning
and see what everyone's advice is before I start ripping the amp apart. I could take
the amp to a qualified tech, but I really want to learn to do this myself, and think that
a sf champ is a good amp on which to learn.
My tools are only a soldering iron and multimeter.
So, first off, the amp has a 2 prong power cord. Secondly, I notice that I sometimes,
but not always, get some clipping (not just typical distortion) when I have the
volume above 7 (or above 5 if I use pedals that increase the signal of my instrument).
I also get some hum/hiss all the time.
The person I bought the amp from said that when he owned it, he had everything checked
out but thought that the filter caps were getting a bit old. I am thinking that replacing
the filter caps would be a good start, as well as retubing, etc.
So, here is a list of what I am considering:
1) Discharge Capacitors for safety
a) get 2 alligator clips & a 5+ watt, 100k resistor.
b) wire together, use this to discharge filter caps
c) connect this to filter cap leads & mains ground
d) I will wear my electrically rated safety boots for the hell of it
2) Replace 2-prong power cord with 3-prong, using a good old UPS cord
a) Ground wire: ring terminal to freshly installed bolt on chassis
b) Hot wire: connect to fuse, fuse to power switch, power switch to transformer
c) Neutral wire: connect to remaining transformer contact
d) Verify:
1) no continuity between hot/neutral and chassis
2) >0 resistance between hot/neutral
3) <1ohm between chassis and tip of ground prong
e) from my understanding, this won't give me problems unless I run into miswired power outlets
3) Replace Filter Cap, using a 20/20/20 mfd @ 475vdc. Not really sure how this works.
This is the one in the cap can? I am assuming it's a pretty simple replacement.
4) Install the Torres "Famous Fender Champ Kit." I have heard mixed reviews of Torres, but this
"Tweedifying" mod looks pretty nice, cheap, and has good reviews.
5) Clean the crackly pots with pot cleaner.
6) Replace tubes with new 6v6s and 12AX7. I have heard mixed results about whether I need to bias
the tubes. Do I need to, and should I install any biasing mods?
Anything I'm missing? Other parts I should replace for the hell of it since I'm already screwing with it?
Safety seem OK? Also, the amp came with a Weber VST 8a125 3.2ohm speaker. Is 3.2ohm acceptable, or do
I need to do something to make this more compatible with the 4ohm amp?
Thanks to any responses. I appreciate any patience, as I really am new to all of this.
I recently purchased an '82 Silverface Fender Champ. I like champs/vibrochamps, and this
one sounds pretty good, but there are a few issues I want to address.
I am new to amp modification and repair, so I want to go through everything I am planning
and see what everyone's advice is before I start ripping the amp apart. I could take
the amp to a qualified tech, but I really want to learn to do this myself, and think that
a sf champ is a good amp on which to learn.
My tools are only a soldering iron and multimeter.
So, first off, the amp has a 2 prong power cord. Secondly, I notice that I sometimes,
but not always, get some clipping (not just typical distortion) when I have the
volume above 7 (or above 5 if I use pedals that increase the signal of my instrument).
I also get some hum/hiss all the time.
The person I bought the amp from said that when he owned it, he had everything checked
out but thought that the filter caps were getting a bit old. I am thinking that replacing
the filter caps would be a good start, as well as retubing, etc.
So, here is a list of what I am considering:
1) Discharge Capacitors for safety
a) get 2 alligator clips & a 5+ watt, 100k resistor.
b) wire together, use this to discharge filter caps
c) connect this to filter cap leads & mains ground
d) I will wear my electrically rated safety boots for the hell of it
2) Replace 2-prong power cord with 3-prong, using a good old UPS cord
a) Ground wire: ring terminal to freshly installed bolt on chassis
b) Hot wire: connect to fuse, fuse to power switch, power switch to transformer
c) Neutral wire: connect to remaining transformer contact
d) Verify:
1) no continuity between hot/neutral and chassis
2) >0 resistance between hot/neutral
3) <1ohm between chassis and tip of ground prong
e) from my understanding, this won't give me problems unless I run into miswired power outlets
3) Replace Filter Cap, using a 20/20/20 mfd @ 475vdc. Not really sure how this works.
This is the one in the cap can? I am assuming it's a pretty simple replacement.
4) Install the Torres "Famous Fender Champ Kit." I have heard mixed reviews of Torres, but this
"Tweedifying" mod looks pretty nice, cheap, and has good reviews.
5) Clean the crackly pots with pot cleaner.
6) Replace tubes with new 6v6s and 12AX7. I have heard mixed results about whether I need to bias
the tubes. Do I need to, and should I install any biasing mods?
Anything I'm missing? Other parts I should replace for the hell of it since I'm already screwing with it?
Safety seem OK? Also, the amp came with a Weber VST 8a125 3.2ohm speaker. Is 3.2ohm acceptable, or do
I need to do something to make this more compatible with the 4ohm amp?
Thanks to any responses. I appreciate any patience, as I really am new to all of this.