Fender Champ Work

[Mattlee0037]

Hey so just picked up a 1981 Rivera era Champ for cheap after I sold my bass (hasn't arrived yet just bought). The insides look to have been worked on a bit. I think I see some orange drops in there, resistors are all carbon comp. The OT has been replaced, but I'm not too sure with what. Are there any common mods that need to be done to these to bring out the best? I'll go over the electrolytics, but beyond that anything?

[xtian]

Is that a Super Champ? I repaired one, and liked it a lot. 12" speaker, push-pull. Much more capable amp than Champ.

Don't worry about mods until you get your hands on it and see how it plays!

[Mattlee0037]

No unfortunately not a super champ just a regular spec one with the blackface aesthetics!

And I suppose I shouldn't put the cart before the horse!

[Mark]

http://www.premierguitar.com/articles/1 ... nder-champ

This the amp in question. They were quite cheap when they first came out.

http://www.stratopastor.org.uk/strato/a ... tslist.pdf

[Mattlee0037]

Yeah I actually read that article, I think that schematic is for the Champ 2 though which uses a different tube compliment as well as a solid state rectifier. Will probably raise the preamp plate voltage like he suggests with the resistor, and replace the output tube, as it may be original.

[Stevem]

Rewire the heaters like a good amp (two well twisted wires), no one leg of the 6.3 volts landed to the chassis like the way they come.
These amps run a ton of plate voltage( way out of class A) even with the 5y3 recto and idle with a good 6v6 way above 40 ma.
If you want to keep the 5y3 recto and not swap in a true 5v4 to drop the B+ voltage, than change the 6v6 cathode resistor to atleast 820 ohms and make it a 5 watter as the are easy to get.
If you got a spare 40 bucks in your pocket, Mojo tone has a OT with a 4 and 8 ohm tap.
If you put that in there is also room in the cabinet for a 10" driver, and having the 8 ohm tap opens up a whole new world of possible speakers to use for a fatter tone and a louder amp.
Just note that on some drivers you may have to cut out a frame rib to clear the can filter hanging from the bottom of the amp.
And speaking of that multi section filter since the amp was made in the early 80s, its time to replace it.
They go for about 34 bucks.

[martin manning]

'68-'82 Champ should have a 5Y3, I believe. Looking at rectifier spec sheets, at 75mA a 5Y3 will drop 36VDC, and a 5V4 only 15. JJ's 5Y3 is true to the old spec re voltage drop.

[Stevem]

With the silver face and these reissue blackface amps the plate voltage on the output will be some 380 to 403 volts dependant on the how strong the output tube is.

[Mattlee0037]

I'll check the voltage before I do anything. What is normally a good range for the preamp/output on these small 5 watters? Hopefully since the OT was replaced they at least changed it with a multitap. I've heard using a princeton OT can increase clarity and bass so maybe I'll try that out. Maybe I'll grab a JJ 5y3 depending on what's in there, I'll check the cap can too.

[Stevem]

A real 5V4 recto wold be the way to go, plus this is a indriectly heated type like a 5AR4, so it will not shorten the life of the tubes by cathode stripping them which is what the 5Y3 does so well unforutnatly!
A princton OT is a push pull type and not what the amp uses, the amp is single ended, plus a 6v6 can at best only do 5.5 clean watts in sitsingle ended form anyway so I see no sence in using a larger OT anyway.
Yes a larger mass OT above stock will give you better bass responce, but having a bit soft low end is what a champ is all about.
Since the amp is not the vibrochamp model, but still uses its PT you can add another preamp tube and get some very nice smooth distortion with nice touch from the amp, unlike the type of saw tooth clipping the amp has now.

[martin manning]

A 5Y3 will drop more voltage than a 5V4, so if keeping the B+ down is desired that would be my first choice. Cathode stripping is not an issue for audio tubes. Lots of Tweed Champs and Deluxes have used 5Y3s, and they do not have any reputation for shortened tube life that I am aware of.

[Mattlee0037]

True you guys are talking sense into me! I'll have to hear the distortion, but a second switchable preamp tube could be fun, or maybe a push pull on the volume pot to bypass the tone stack. Who knows!?

[Firestorm]

True you guys are talking sense into me! I'll have to hear the distortion, but a second switchable preamp tube could be fun, or maybe a push pull on the volume pot to bypass the tone stack. Who knows!?

Bypassing the tone stack is definitely a useful option. Simple to do: you just lift the ground on the "mid" resistor. Swap out a pot for one with a push-pull switch.

If you add another preamp tube, you'll also need some kind of attenuation or you'll drive the 6V6 into cutoff, which you won't like.

[Mattlee0037]

Mid resistor? And would I be able to add half a gain stage without the attenuation?

[Stevem]

The added gain stage would be for overdive use.
You can find many ways on line to tap off some B+ to power a Opto coulper to switch the gain stage in and out.
The whole circuit for both the added tube stage and the switcher and its power section can be placed on a little section of circuit board and placed on stand off`s.