Got a '68 SF Champ: Pics and Questions Inside

[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.