Got a '68 SF Champ: Pics and Questions Inside

[Commodore 64***]

OK, I just brought home what is purported to be a '68 Silverface Champ. Seller said it had new tubes 3 years ago. Gonna post some pics, then ask some questions...








Questions:

1. The tube diagram says Bronco Amp. I understand that a Bronco is a student version of the vibrochamp. This isn't a VC, obviously, but it does have a label on the backplate that says "Vibrato Pedal", but no output for such a thing. What gives?

2. Early SF amps may be wired to BF spec..is this true? If so How would I figure out how my Champ is wired?

3. I seem to have a removeable baffle. THis is great news right?, I can now see if I can finagle a 10-inch speaker in there by creating a new baffle and keeping the stock one unharmed.

4. Volume wise, I had a Black Heart Little Giant. It too, is a 5w amp, and it was frickin LOUD. This Champ though, I can dime it and not blow my ears off. I gotta dime it to get any type of speaker break-up. It's not quiet by any means, but it's nowhere near as loud as my BHLG. I'm totally fine with the level of output, but I'm just wondering if the Champ may need a cap job or something?

4. People talk a bout a speaker out..that is like an RCA jack? My Amp doesn't have this. What gives?

(I cross posted this over a TDPRI, so if you frequent both forums, that might annoy you)

[markb]

From The Fender Amp Book - John Morrish

Bronco

Effectively the Vibro Champ with its name in red to match the Bronco student guitar

The listing lets me down here because the valve complement differs from that for the Vibro Champ.

You're probably looking at a factory error. Maybe they were out of Champ charts that week?

[markb]

As for your other questions.

2. Don't bother. Fender didn't really change the smaller amps that much.

3. A popular change for Champs.

4. Your third picture shows the speaker jack.

(the other) 4. Older amps have less gain. Times change.

[Commodore 64***]

As for your other questions.
4. Your third picture shows the speaker jack.

Actually the 3rd pic shows a label for a jack, but there's no jack.

[markb]

No jack? That cable doesn't pull out? My bad, then but it looks like one of those RCA connectors without a cover that Fender used a lot for reverb and footswitch connections. They're often corroded and hard to disconnect.

[Commodore 64***]

Hmm, let me take the back brace off again and give it another look.

edit: You were right. It's an RCA type cable. I just played around with the amp for another hour, I put a Monte Allum modded Blues Driver pedal through it, and it gets plenty of volume with that thing in front. What a great little practice amp!

It gets a cool fuzzy tone if I crank the tone knob on my Jazzmaster (P90s) way down.

Only thing missing is reverb, but it still sounds pretty cool to me.

[Commodore 64***]

What does a microphonic tube sound like? At volume levels past ~6, I'm getting what sounds like a high pitched vibration tone. It's not super loud, but definitely noticeable.

I'm 99% sure its the 5Y3 rectifier tube. It's very loose in the socket and vibrates when the amp is cranked past 5 or 6. I am going to retube this thing for sure, just because, so anyone know where would I get some retention clips?

[sumitomo]

What does a microphonic tube sound like? At volume levels past ~6, I'm getting what sounds like a high pitched vibration tone. It's not super loud, but definitely noticeable.

I'm 99% sure its the 5Y3 rectifier tube. It's very loose in the socket and vibrates when the amp is cranked past 5 or 6. I am going to retube this thing for sure, just because, so anyone know where would I get some retention clips?

Be careful!!!Sumi

[Commodore 64***]

It's just a rattling 5Y3.

I'm gonna recap and retube this. I am considering just doing 3 separate caps instead of the buying a 20/20/20 can. I need to find a schematic on how to do this though.

ALso, I can get a RCA NOS 5Y3 rectifier from Eurotubes for 30 bucks, but I also ran across this copper 5Y3 . I'm considering going with the copper since it is purported to be easier on the output transformer and I'd like to keep that sucker vintage. Any opinions on this?

[tunghaichuan***]

In the BF and SF Champs, you definitely want to use NOS 5Y3 tubes. The Russian Sovtek "5Y3" isn't really a 5y3. If you use it, your voltages will go up. Two real (i.e., NOS) 5Y3 tubes will probably last a good, long time.

I don't have any firsthand experience with the Copper Caps, but I remember a couple of people complaining that their Copper Caps overheated to where the solder melted on the pins. Not good.

I know of techs who have hollowed out the cap can and replaced the contents with three discreet caps to keep the vintage look.

If your not so concerned about the vintage value, then Eurotubes sells an inexpensive multisection cap:

https://ssl.eurotubes.com/cart/index...category_id=27

You want the: 20 X 20 X 20 X 40 X 500 Volt Multisection and the clamp that goes with it. I would use the first 20uF section for the input cap (from the 5Y3), double the second and third 20uF sections for the screen grid node on the 6V6 and use the last 40uF section for the 12AX7's anodes.

Schematic and layout: http://www.schematicheaven.com/fende...a764_schem.pdf

Your '68 Champ should be identical circuit wise to the earlier Blackface version. CBS only changed the cosmetics for the silverface versions of the Champ and Vibrochamp, early on at least.

It's just a rattling 5Y3.

I'm gonna recap and retube this. I am considering just doing 3 separate caps instead of the buying a 20/20/20 can. I need to find a schematic on how to do this though.

ALso, I can get a RCA NOS 5Y3 rectifier from Eurotubes for 30 bucks, but I also ran across this copper 5Y3 . I'm considering going with the copper since it is purported to be easier on the output transformer and I'd like to keep that sucker vintage. Any opinions on this?

[Commodore 64***]

Thanks Tung. By the time read your post, I already had made the following order from Weber.

1 item WY3GT subtotal = $ 22.00 (No Tax)
Octal Rectifier

1 item AlNiCo Signature 8S subtotal = $ 35.00 (No Tax)
AlNiCo 8 inch Weber Signature Series Speaker
* Impedance - 4 Ohms -- 8sigA-S4

1 item EC20x4-450 subtotal = $ 30.00 (No Tax)
Cap Can, 20uF x 4, 450VDC
* Mounting - No Wafer

1 item EC225-50 subtotal = $ 0.45 (No Tax)
Electrolytic Capacitor, 2.2uF, 50VDC

2 items EC256-50 ($ 0.55 each) subtotal = $ 1.10 (No Tax)
Electrolytic Capacitor, 25uF, 50VDC

1 item MFR1K-5 subtotal = $ 0.27 (No Tax)
Resistor, Metal Film, 1K Ohms, 5 watt

2 items TR-34 ($ 1.80 each) subtotal = $ 3.60 (No Tax)
Spring Tube Retainer, EL34

I'll try that copper rectifier, jsut for the helluva it sicne I ordered it, but I'm probably going to get a retube kit from Eurotubes for 53 bucks plus shipping which includes a NOS RCA 5Y3. I was also going to jumper the firsr 20/20 on the cap can with a 5w 2.2k ohm resistor, which is supposed to lower the voltage and get rid of hum.

Once I retube and recap, and replace the 8-inch speaker, I'm ultimately going ot go with a 10 -inch Weber, one of the expensive alnicos, but I'm saving that expenditure for a few months down the road. Fishing season is nearly upon me and I'd have to make a new baffle.

[Brian Krashpad]

I dunno nuffin bout all those tubes and letters and shit, but CONGRATS!

Bosstastic.

[Commodore 64***]

I played the crap out of it last night: , volume set about 5, treble 7, bass 3 with Allum Modded Blues Stack Pedal (level and tone at 12 o'clock and gain at about 2 o'clock) and just used the guitar (MiM Strat) volume to vary the tone.

Loved it. Wondering if I need that Weber speaker in there at all.

[Commodore 64***]

Ok, so all my stuff is set to arrive today, and I ordered some other stuff from Eurotubes in the meantime too. I have to go out of town tomorrow, for my company's annual meeting, so I won't get to start the Champ surgery until sometime next week. I have some choices to make, mainly these:

1. Keep original Stock Fender speaker or install the Weber Signature 8 Alnico.
2. Use the Weber Copper Cap rectifier or the NOS RCA 5Y3.
3. Use the vintage spec 20/20/20/20 cap can from Weber, or the one I just ordered from Eurotubes, a JJ 40/20/20/20 (as suggested by tunghaigichan)
4. Replace the RCA speaker output with a standard 1/4" switchcraft jack, or leave it stock.
5. Try to locate a 2.2k ohm 5 watt resistor for the cap can mod to reduce plate voltage and 60hz hum.

And then of course I will be replacing the other electrolytic caps in the amp, and installing new JJ 6v6 and ECC83S (12AX7) tubes.

[tunghaichuan***]

Ok, so all my stuff is set to arrive today, and I ordered some other stuff from Eurotubes in the meantime too. I have to go out of town tomorrow, for my company's annual meeting, so I won't get to start the Champ surgery until sometime next week. I have some choices to make, mainly these:

1. Keep original Stock Fender speaker or install the Weber Signature 8 Alnico.

Try both and see which you prefer, it isn't hard to swap out a speaker. When you try the Weber, give it time to break in. It will need several hours of hard playing to loosen it up a bit.

2. Use the Weber Copper Cap rectifier or the NOS RCA 5Y3.

I vote for the NOS RCA 5Y3. Keep the CC as a spare in case the NOS 5Y3 goes south on you.

3. Use the vintage spec 20/20/20/20 cap can from Weber, or the one I just ordered from Eurotubes, a JJ 40/20/20/20 (as suggested by tunghaigichan)

If you use the Eurotubes cap can, you will need to make sure that you only have 20uF on the 5Y3. Too much capacitance will wear out the tube prematurely. So it will be kind of inconvenient to use that cap. Since you have both, I'd use the Weber cap. Use the first 20uF cap for the first section, put the second and third 20uF caps for the second and use the last 20uF section for the preamp tube.

4. Replace the RCA speaker output with a standard 1/4" Switchcraft jack, or leave it stock.

I vote leave it stock. Any mod like this will devalue the amp. Changing tubes and caps is expected because they wear out. Changing the speaker doesn't count because it is easy to swap it out. You may get lucky and the 1/4" jack will fit the RCA jack hole without modification so don't bore out the hole if it is too small to accommodate the 1/4" jack.

5. Try to locate a 2.2k ohm 5 watt resistor for the cap can mod to reduce plate voltage and 60hz hum.

Don't know about this one, what exactly do you do to install this mod?

And then of course I will be replacing the other electrolytic caps in the amp, and installing new JJ 6v6 and ECC83S (12AX7) tubes.

If you swap out the electrolytics on the preamp tubes' and power tube's cathodes, you can use from about 1uF to 10uF. The stock value is 22uF which can make the amp sound to flubby.

For the 6V6 you can use a fairly large cap, like 1,000uF to 2,200uF even 4,700uF, but make sure the voltage rating is over 50v or so. The only problem is that those caps are very big, physically.

[Commodore 64***]

Don't know about this one, what exactly do you do to install this mod?

You bridge some lugs on the cap can, which is supposed to lower the plate voltage a little which is better for the tubes.

If you swap out the electrolytics on the preamp tubes' and power tube's cathodes, you can use from about 1uF to 10uF. The stock value is 22uF which can make the amp sound to flubby.

For the 6V6 you can use a fairly large cap, like 1,000uF to 2,200uF even 4,700uF, but make sure the voltage rating is over 50v or so. The only problem is that those caps are very big, physically.

OK. I ordered 25uF for the preamp and power tubes. What do you mean by flubby? I'll consider the other values, especially because I may need to order another resistor, so I need to make shipping worthwhile. If I plan to retrofit this amp someday with a 10" speaker, would that "flubby" be something I wish I had?

[tunghaichuan***]

OK. I ordered 25uF for the preamp and power tubes. What do you mean by flubby? I'll consider the other values, especially because I may need to order another resistor, so I need to make shipping worthwhile. If I plan to retrofit this amp someday with a 10" speaker, would that "flubby" be something I wish I had?

By flubby, I mean trying to push too much bass through the small 8" speaker, it sounds just plain bad, IMHO. It doesn't depend on speaker size, either. I use 12" speakers with the Champ circuits I've built and I've found that 2.2uF or 4.7uF sound good.

[Commodore 64***]

Your opinion is good enough for me. I will grab some 2.2uf and 4.7uF electrolytics. As long as I'm in there, should I replace the film caps? I'm looking at the schematic and I can't read some of the numbers. Folks mention Mallory 150s a lot, but there's a bunch of different ones and I don't know which to order.

[tunghaichuan***]

Your opinion is good enough for me. I will grab some 2.2uf and 4.7uF electrolytics. As long as I'm in there, should I replace the film caps? I'm looking at the schematic and I can't read some of the numbers. Folks mention Mallory 150s a lot, but there's a bunch of different ones and I don't know which to order.

Don't take my word on it, try it for yourself and see if you like it. I was only making a suggestion based on my personal experiences.

Film caps don't dry out like electrolytics do, so you don't have to change them. If you want to, there are three in the tone stack 250pF, a .1uF, and a .047uF, these are usually rated at 600v or better. The 250uF cap is usually ceramic or silver mica.There is another decoupling cap between the second 12AX7 stage and the 6V6 power tube. It is a .022uF cap. I forget what the stock rating is, but I usually use 600v rated parts.

It's been a while since I looked into caps, but there are a few types: polypropylene, polyester, ceramic, silver mica. From my experience, Malory caps are slightly brighter than Orange Drop types, but I doubt I could pick them out in a double blind test.

You should be able to find Malory or Orange Drop type caps in .1uF, .047uF and .022uF values. As I stated before, the 250pF (220pf) is usually ceramic or silver mica.