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Old 22nd October 2006, 12:57 AM   #1
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Default Fender Champ 5C1 help needed!

m starting on a replica of a Fender Champ, in all of its ridiculous simplicty. (5C1 variant, http://www.drtube.com/schematics/fen...-5c1-schem.gif ). However, I realized I've just goofed: I bought a transformer (though rated for a 6v6) rated for only five watts (not eight), and with an input impeadance of 3.8k vs. the 4k normally used. It is, however, rated for a 6v6 when single-ended, and it's not like I'm looking to build a monster anyway. Should I forget it and blow another 30$ on a proper Champ output transformer, or give it a shot? ( http://www.tubedepot.com/tr-ot-01.html)

Linky to now-ended FleaBay auction for my not-quite-right transformer:
http://cgi.ebay.com/ws/eBayISAPI.dll...1249&rd=1&rd=1

This is also a "budget" amp, but that's not to say I'm going to do a shoddy job with the components. From what I've read, carbon composition resistors do funny things at high voltages, resulting in desirable distortion. (And they're traditional!) .5w "NOS" carbon composition resistors from Tubedepot are $0.25 each; I think that these will work for everything but the 500 ohm resistors tying the 6v6 to ground and the two PSU caps together. (For these, I was going to use two in parallel.)

Rectification and the power transformer is another issue altogether. I'm looking for a way to provide power cheaply; what would you reccomend? A 5Y3 is about 6$ on eBay, but I can't even figure out what on earth to use for the power transformer. I do know that the Fender Champs used somewhere in the neighborhood of 300-320v.

Cheap isolation transformers capable of supplying 150mA @ 120v are not hard to find. What if I wired two in series to form a 240v center-tapped transformer, and used some ordinary diodes to produce about 340v; this could be dropped later by resistors, perhaps? This option is the most appealing: As opposed to a 10$ tube and a 40$ transformer, I can use three 5$ transformers and 1$ worth of diodes.

I'm also curious as to what I should use for the gain control potentiometer. Tubedepot's kit uses a cheapie CGE potentiometer; they have them for under 3$. Should I spend some more money to get something of better quality, perhaps a homemade stepped attenuator? Also, what about the input capacitor? A sprague "Vitamin Q" at the specified 600v/.02uf should only be a few bucks. Or should I go for something else instead?
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Old 22nd October 2006, 01:06 AM   #2
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Try this transformer, it should work well.
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Old 22nd October 2006, 01:18 AM   #3
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Quote:
Originally posted by Wavebourn
Try this transformer, it should work well.

You mean the output transformer?

Good to hear.
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Old 22nd October 2006, 01:29 AM   #4
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Quote:
Originally posted by Spasticteapot



You mean the output transformer?

Good to hear.
Yes. Which is 3.8K for 5 W.
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Old 22nd October 2006, 01:31 AM   #5
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Quote:
Originally posted by Wavebourn


Yes. Which is 3.8K for 5 W.
Awesome.

So, what should I do for the power trafo?
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Old 22nd October 2006, 01:38 AM   #6
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Quote:
Originally posted by Spasticteapot


Awesome.

So, what should I do for the power trafo?

Did you look at industrial transformers?

They are 208/240/480V primary, 120V secondary.
If to use 120V as primary, you may get 240-0-240 on secondary
(240*1.412=338V)

No need to drop by resistors, 6V6 will live with 330V on the plate well.

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Old 22nd October 2006, 02:24 AM   #7
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Quote:
Originally posted by Wavebourn



Did you look at industrial transformers?

They are 208/240/480V primary, 120V secondary.
If to use 120V as primary, you may get 240-0-240 on secondary
(240*1.412=338V)

No need to drop by resistors, 6V6 will live with 330V on the plate well.

Thanks for the tip!

Should I use the unmodified 5C1 circut?
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Old 22nd October 2006, 02:50 AM   #8
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Quote:
Originally posted by Spasticteapot


Thanks for the tip!

Should I use the unmodified 5C1 circut?
Yes!

I'd suggest you to use couple of 1N4007 diodes instead of a tube rectifier. Also, you may try 6SK7 instead of 6SJ7 if you play solo, may be you'll like the sound with it.

Instead of 6SJ7 you may use 6J7. It is the same tube, but with a grid cap.

Also, 6AK5 will work well. You may try 6BE6 instead of it for a sweet sound.

Don't run for audiofile volume pots and capacitors, you don't need them. Try and make own conclusions.

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Old 22nd October 2006, 03:00 AM   #9
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Quote:
Originally posted by Wavebourn


Yes!

I'd suggest you to use couple of 1N4007 diodes instead of a tube rectifier. Also, you may try 6SK7 instead of 6SJ7 if you play solo, may be you'll like the sound with it.

Instead of 6SJ7 you may use 6J7. It is the same tube, but with a grid cap.

Also, 6AK5 will work well. You may try 6BE6 instead of it for a sweet sound.

Don't run for audiofile volume pots and capacitors, you don't need them. Try and make own conclusions.

Actually, I don't play guitar. I just wanted to try building one. (Crazy, eh?)

For the princely sum of 15$, I obtained a genuine set of Westinghouse tubes from around 1960; a 6SJ7 and a 6v6GT.

What's the advantage of the diodes over a tube rectifier for a two-diode configuration? It would seem that 240v is all that's necessary if a bridge rectifier is used; so long as I'm going with a big power transformer, why not spend the extra 8$?

I also found a place selling 280vct transformers for 10$, so yes, my decision is influenced.
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Old 22nd October 2006, 01:18 PM   #10
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Quote:
However, I realized I've just goofed: I bought a transformer (though rated for a 6v6) rated for only five watts (not eight), and with an input impeadance of 3.8k vs. the 4k normally used. It is, however, rated for a 6v6 when single-ended, and it's not like I'm looking to build a monster anyway. Should I forget it and blow another 30$ on a proper Champ output transformer, or give it a shot?

The Champ WIDE PANEL , or commonly refered to as the 5C1 only has an output of 4W. Generally most early champs used a 5K output transformer and there are plenty of suitable transformers under $20.00us
Examples:
EDCOR @ 18.64 +SH
Triode Electronics Champ replacement @16.95 + SH

Or even 1 better, A matched set Power/Choke & Output is regularly listed on Ebay by Triode Electronics for the 5F1 Fender Champ or 5F2 Princeton @ 70.00 +sh Which could easily be used also.

Part of the Charm of a Champ is in the 5Y3 rectification, The Noise, The Sag Ect, Solid state works well, But you do loose some of that vintage color.

To bad you bought those other transformers, I bet this Chassis/Board/Power Transformer set goes budget/cheap tomorrow on EBAY

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