Fender Champ

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CJ

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boy these amp threads are exciting, aren't they?  :eek:

here is a silver face champ, somebody wants a 3 prong chord put on it,

but i bet what they really want is less hum,

 

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easy to work on this chassis,

see that green wire that goes to the ground tab, that is a cheap way to wire heaters because kids don't care about hum when they find this thing under the tree at age 10,

Leo knew this, keep the price down any way you can, parents dont care about a little hum, the kid is locked in his room, they are watching Bonanza and drinking gin fizzes in the living room,

 

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this amp does have the brass plate under the controls, so no skimping there,
familiar components from the Fender stock room,
with the possible exception of the 6V6 bias resistor and cap,

see those two 100K plate resistors that are  joined in that triangle?
those are gonna get changed to 1 watt carbon as the 1/2 watts start to snap crackle and pop, this is very common in early Fender stuff,

 

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this is the new chassis, soldered transformer wires like the old days, got rid of the solder lug,

this pwr trans had a heater winding CT which was snipped, why not splice a wire on there and use it to kill hum?
so we did, and twisted up some green wires to feed the tubes like the big amps have,  no more heater hum,

also got those new plate resistors in there,

and we sound checked some different value caps in the first stage cathode,
found that 1,5 uf sounds better than 25 uf,

also changed pwr supply resistors to the 5F1 Camp circuit, which has the best tone out of all the different versions,

 

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looks like the speaker has been changed, don't know what brand,

luckily they did realize that this amp wants a 4 ohm instead of 8, so we don't have to add more wire to the OPT secondary,

 

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here is the best sounding Champ circuit, no tone controls so they can get away with less gain from the missing cathode bypass cap on the first and second stage,

dropping resistors in supply are 10K and 22K instead of 1K and 10K,
this saves the pwr tube a bit as the screen now sits below the plate, and also lowers B+ to preamp stages for warmer tone with a bit less gain,

feedback resistor is 22K instead of 2.7K and is applied differently, no second resistor added to cathode circuit like the later amps,

these SE amps are sensitive to tube choice, if you are lucky enough to have a stash of different 6V6 tubes then you can fine tune the amp,

notice less capacitance in the filter circuit, this changes the sound for the better,
you don't want to over filter this amp,


 

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here is the silver face circuit with the 5f1 mods we did,

found that we needed some capacitance on the firat stage cathode as without it, gain dropped off too much,

and we liked the feedback circuit from the silver face a bit better and that means we keep the second stage cap which keeps the gain up there so we can torture the speaker a bit,

stick in a new pilot lamp #47 and bolt it up,

 

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> speaker has been changed, don't know what brand,

Possibly an Eminance geetar speaker. Not a wrong choice. You might re-check your mods with a known-good-for-Fender speaker. 1.5uFd under the front end is light, and suggests the Emmy isn't taking bass as well as what Leo put in it. You will sure miss the extra 23.5uFd when you plug the Champ into a Full Stack.

> feedback resistor is 22K instead of 2.7K and is applied differently

As you say, without the tone controls they had a LOT more gain on tap. This is the cheap amp so it can't have more gain than the hi-price models. The 2K7+47 on the AA champ makes the most of what little gain is left after the tonestack was jammed in.

Personally I'd accept that it IS an AA amp, and add the missing MID control, raise the 2K7 NFB, and experiment with different speakers.
 
that's why all the amp threads,

I am enjoying them immensely. I pass time by watching amp repair vids on Youtube, some of them are HORRENDOUS.

Check out Roy Blankenship's amp repair video, a lot of fun.

https://www.youtube.com/watch?v=rz3XDNmiIvo

 

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