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Cheap Champ - For Moonpie and others

songsmith1950

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Jan 20, 2005
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213
I am in Moon! First of all if you are checking your filter caps, and you are VERY sure they are discharged, use the ohm meter. Good electrolytic caps will first dip down to zero or very near and then increase in resistance as they charge. If there is no dip they are bad. If there is no rise they are bad.

As far as the speaker goes I would get a Weber signature 8 to go in it but I would also install a jack so it can be run to an external cabinet. You would not believe what a Champ into a really good speaker or cab sounds like. Even into a good 8 it can be something really nice. I would keep the original though just in case you want to sell it someday. People are touchy about that.

I bet the original tubes are still just fine. Champs didn't really burn up output tubes very quickly at all and preamps are sometimes good for the life of the amp or longer. The rectifier tube should also still be fine.

Did the guy replace the power tranny or the output tranny? If it works it is probably fine anyway, but just for knowing.

Oh, ladies who solder are certainly keepers! Protect Mrs. Moon at all costs. Just make sure you program the phone for 911 to save time.

This can be fun.

Tom

Songsmith
 

moonpie

In the Zone
Joined
May 24, 2003
Messages
9,781
Hey, I never said we were gonna do it all today.

I'll get some real good pix of both sides(top, bottom, left end, right end, front, back....you know, both sides) of the chasis over the weekend. Even get some pix of the pots so folks will know how to figure date codes, etc....

I think this would be a good project because it's exactly what someone would see on ebay as a "project"....I've even got a Fender logo with the tail (it's on my Peavey Classic 30 right now) that I could put on the amp and play ignorant and say


ELVIS GAVE ME THIS AMP THE MONTH BEFORE HE DIED.....

...might go for some of those exorbitant prices.......

This could be a good thread to educate people on the Champs and also how to avoid being ripped off if I decide to put the script logo on it...why should I rebuild it if I could clean it up...say I got it from my Dad who bought it brand new FOR ELVIS.....who gave it to me a month before he died.....and I'm selling it for a friend....

I sure appreciate y'all checkin' in.
Tim, was I right in remembering you as one of the fellows who tried to explain this stuff?

I'm really hard to teach, and that's another reason I think this would be a good project.

For me, it's hard to understand theory, but I'm good at hands on experience.


I'll get some pix this weekend. The chasis isn't mounted in the cabinet right now....we'll have to leave some things to the imagination...

but we CAN take it from there
 

Tim C.

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Messages
6,484
Moonie,

Yes it twas me who had two threads going on amp theory. I wish the second one hadn't disappeared because I had put a lot of work into that one. I did drawings, etc to help make it easier to understand how these things work.

Tim C.
 

moonpie

In the Zone
Joined
May 24, 2003
Messages
9,781
Champ_amp004.jpg




OK...here's what I've got....

The tubes are USA General Electric 6K6 and 5AR4/GZ34.....different than what the tube chart calls for.

The preamp is an English Westinghouse 12AX7A.

I'll try the Weber speaker and plan on wiring a speaker jack in.

Should I replace the tubes also , since they differ from the chart?

Looks like the Power Transformer is the one replaced. The numbers are
M0227?2
EIA606?140
UL 1411

The Output Transformer
022905
606-3-37

Looks like the PT has been burned. Notice along the top edge

Champ_amp016.jpg
 
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songsmith1950

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Jan 20, 2005
Messages
213
I think I would possibly replace the tubes, even though the 6K6 is a lower power tube than the 6V6 and should not be any problem at all. The 5AR4 does not drop as much of the plate voltage as a 5Y3 would. That can cause problems in an amp that doesn't like voltages quite that high. It also would greatly reduce whatever sag you might get at higher volumes. I would surely put a 5Y3 in there.

The preamp tube you can keep. YOu can actually keep the 6K6 as well but I would surely put a 5Y3 rectifier in it.

I think the power tranny surely looks suspect. As inexpensive as they are and with the delightful solder lady at your side I think I would replace it. My own choice would be to find one with a lower B+ if you can in order to keep the smoother overdrives and softer sounds one of these can make. Also better on all the parts you keep.

The cap can may or may not be good. Once you get her running and power her up you will know pretty quickly by the presence of hum. If there and loud the cap can needs replacing. If not I wouldn't bother with that yet.

Just my own thoughts Moon. I think a power tranny and 5Y3 would get you going just fine. Oh, and the Weber alnico.

Tom

Songsmith
 

Tim C.

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Jul 15, 2001
Messages
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Moonie,

Are you sure the power tranny was replaced? Looks like an original to me.

I would get the 5AR4 out of there and put a 5Y3 in and definately get that 6K6 outta there pronto. It is a lower output tube and cannot handle the voltage your amp is putting out. I would not change the power tranny to a lower B+ model. That changing tranny's to a lower B+ craze all started because the tranny's in tweed Fender's were designed for wall currents running around 110v to 115v max at the time. Now outlets are putting out closer to 120v. Your amp is a later silverface designed later than the tweeds obviously and there is really no need to compensate for the wall voltage.

Tim C.



Tim C.
 

moonpie

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May 24, 2003
Messages
9,781
Hey, Tim...thanks....

The tech used a transformer he had in his parts bin, so it's possible it was out of another Champ.

Which caps should be replaced, just as a rule of thumb, because they're over 10 years old?
 

Tim C.

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6,484
Well, you want my honest opinion? None....unless they are causing you a problem. I know, I know....there will be a whole clan of folks who feel you must replace the filter caps and cathode bypass electrolytics or the amp may blow a tranny, etc. I am not necessarily of that group. I am old school. I did tube radio repairs in a TV repair shop in the early 1970's. You replace filter caps when the amp starts to hum and the cathode bypass caps almost never. Cathode bypass caps operate in a very low voltage area and generally have less than 2 volts on them so they almost never go bad.

The main reason to consider replacing any bypass caps would be to take some of the muddiness away from the tone of the amp by going to a smaller value cap on the first triode.

Let's look at your amp a minute. Starting from the left side of the picture you see a small 1/2 watt 1.5k resistor and that white thing next to it is the cathode bypass cap I was talking about. It will be 25 microfarads at 25 to 50 volts.

Next to those working left to right are two 68k resistors which are called input grid resistors. They connect directly to the grid of the 1st pre amp stage. The next two caps positioned directly next to each other are the bass and midrange tone caps. One will be a .1 mfd and the other a .047 for mids. Connected to that will be a small ceramic round disc which is a 250pf treble cap and off that will be a 100k slope resistor which controls how much bass and mid pass through the circuit. Lowering the value of that resistor will increase overall gain because it increases upper mids.

Then you will see two resistors color coded yellow brown black. These are the 100k plate load resistors which connect to the two plates of the first preamp tube.

The next big blue capacitor is the coupling cap to the 6V6 output tube.

Now see that bigger resistor with the white capacitor attached to it? That is the two components that bias the single 6V6 output tube into class A operation. They are, a 2 watt 470 ohm resistor and a 25 mfd electrlytic at 25 volts.

Hope this helps.

Tim C.
 

songsmith1950

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Jan 20, 2005
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Though I have also been in tube electronics since the 60's I think I will just walk away before this becomes something it was never intended to be. I do not follow crazes or mystical tone theories that are sometimes quite absurd.

There are other reasons for lower B+.

Regards to all

See you in the ZamZone Moon!

Tom

Songsmith
 

Tim C.

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songsmith1950 said:
Though I have also been in tube electronics since the 60's I think I will just walk away before this becomes something it was never intended to be. I do not follow crazes or mystical tone theories that are sometimes quite absurd.

There are other reasons for lower B+.

Regards to all

See you in the ZamZone Moon!

Tom

Songsmith

Song,

No one is trying to run you off.

Yes, there can be other reasons for lower B+ but why in a Champ? It is a 5 watt amp. There is only so much tone you can get out of them with the small speaker, etc. Why have Moonie go out and spend a bill on a tranny that won't maker a whits difference. But tone is subjective so if you hear a difference with 20 volts or so less B+, go for it. And if tube life is an issue, new production 6V6's are cheap. Just my 2 cents.

Tim C.
 

juniorspecial

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May 6, 2003
Messages
4,232
Hey Moonie,

When you get that done, polish it up nice and bring it up to Ann Arbor for a little jamma-lamma!!

:dude
 

moonpie

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May 24, 2003
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You got it, Junior :eek:la

Tom, please stick around. I'm sure it won't turn into theoretical arguements. Both of you are being very helpful.
I'm just an ear in the Zone these days. My joints have been pretty painful the past few weeks. Maybe soon I'll be back to making noise.



Tim, identifying the caps and resistors was exactly what I needed. Things make a little more sense.
In keeping with the "cheap" aspect, I'll hold off on the transformer and caps for right now.

Since it's been so long since I've heard any noise out of it, it makes sense to get my speaker and the right tubes and see what happens.

I'll get busy cleaning up the cabinet and hardware.

Thanks y'all:eek:la
 

Tim C.

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Moonie,

In reference to your power tranny, I looked at the numbers you posted again and am even more sure that tranny is from an orginal Champ or Princeton. The number 606 indicates it is a Schumacher brand tranny which coincides with what Fender used for many years. The wire color coding coming out of it is exactly the same as an original Champ tranny as well.

The number on your output tranny is deciphered by the julian dating system as this

606-3-37

606= Schumacher, the manufacturer
3= the year, in this case 1973
37= the 37th week of 1973

So, your output transformer was manufactured on the 37th week of 1973. I am assuming the replacement power tranny is probably a 1971 from the number you posted off it. But the question mark makes it still....a question.:lol

Tim C.

Edited for my poor typing skills. I am a two finger pecker you know.:lol
 
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Tim C.

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Moonie,

There are a couple bare wires coming off the circuit board that are soldered directly to the chassis. These are ground wires and many times come loose fro the chassis over the years causing the amp to loose power and hum. You might want to check them to see they are properly secured.

edited to add:

Oh, I forgot. I build a souped up Champ style amp from scratch for local music stores. I found the Jensen C8R 4 ohm speaker to be about the best bang for the buck out there. It is a 25 watt speaker and they run about $30.00. Nice original style seamed thin paper cone speaker for low dollars.
 
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keef

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Jan 27, 2002
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5,005
moonpie said:
The tubes are USA General Electric 6K6 and 5AR4/GZ34.....different than what the tube chart calls for.

The preamp is an English Westinghouse 12AX7A.

FWIW: I have a '76 Champ which still has its original RCA's.
 

songsmith1950

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Jan 20, 2005
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213
Sorry. I guess I just have my own ideas in a Champ. The route Tim is advising is perfect for restoring a Champ. That is certain. Very budget concious but at the same time it will restore a Champ to all it was, which is legendary.

Kinda got caught I guess. I am in the process of developing a Champ type model with reverb and trem that has several selectable features to increase or decrease gain, breakup, and headroom.

My goal in this amp is to give a Champ with most everything including the capacity to break up at an even lower volume level. Even if I can not attain the lower volume level part, which I am hoping I can, it is something I want for my own studio use.

Tom

Songsmith
 

Tim C.

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Glad you are back Tom. We all need each other.:) Your Champ idea sounds fun! Let us know how it turns out.

Tim C.:)
 

songsmith1950

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Jan 20, 2005
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Sure will! Right now deciding whether to really go for it and add the three knob reverb or just the single. So many things. Also switchable caps with the cathode resistors to add subtle gain in the first two stages. I know these are in the AA764 and CBS Champs but I am basing off the 5F1.

I say probably the Three Knob with the 6K6 rev tube because the Tweed Champ is really the amp I wish to base from and add top of the line additions to. I have a Gretsch 5162 Compact TremVerb which is kinda like a Champ with verb and trem but it does not get the Champ tone quite right and the verb tank is a cardboard box that leaves much to be desired. I do love the little Gretsch but want something a few miles advanced. Oh, I did add the Pentode/Triode switch to the Gretsch and it does nice things if you like a darker smoky tone with less volume. With blues that is fine.

Also, I know a Champ has an 8 and actually can make one sound pretty darn good but I run my right now through a Ceramic 12 in a Deluxe Reverb. Have a Weber alnico 12A125 on order but haven't got it yet.

Still in process of getting ideas and developing them, but looking forward to hopefully being able to jam in studio with all the goodies in really good quality.

Thanks, Tim, I needed that. And yes we all do need each other.
Tom

Songsmith
 
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