Fender SF Champ re-cap parts

[ampdan]

To the OP. That amp looks bone stock to me. I've seen several with the 40-20-20 cans.

[Phil_S]

I was thinking the same as Martin, so I just checked the RCA manual. It says 20u for 700VAC input and 10u for 1000VAC input. That puts the Champ squarely at the 20u max. Duncan's TDSL says 32u is the max. 40u seems to me to be excessive for the rectifier tube. Also, I can't imagine needing more than 20-20-20 for the Champ. By contrast I think the 5E3 uses 16-16-16. 3x 20u is plenty of filtering.

I'm also not someone who'd be so quick to part with $30+s/h for a can cap though I can understand there may be aesthetic considerations. Unless this is a collector's item and you mean to keep it fully "collectible", I think I'd be inclined to use three caps and find a place inside to put them. Someone posted a picture of a decent implementation of this. You can get perfectly good caps for a whole lot less money than you'd spend for a can cap. Also, this business of original spec (-20/+50%) seems upsurd to me. Modern caps are made to much better tolerance at lower cost. I guess I'm just missing the point, or ami I?

[rp]

Without reading through the whole post again, I'm not sure what the issue is, AES/CE has the exact cap: C-EC20X3-525 - I believe it's the correct diameter but double check. I'm pretty broke right now but $30 amortized over 20 years is a good deal. Get an insulator too in case you break the original getting the cap out.

As for getting it installed. There's a recent post on using big soldering irons for this. It's a chance to buy a new tool, or used off ebay. Roof and gutter, stained glass, guys use these irons too. Maybe you know one?

https://tubeamparchive.com/viewtopic.php?t=13355

If you are here it must be cause you respect these old amps. Cheap out on the next car repair or live with the drippy faucet for another year but do right by the Champ, replace it properly.

[Firestorm]

I agree with Martin, Dan and Phil that the amp looks factory stock. On the side of the Mallory can cap, there will be an EIA code that will tell you the date of manufacture of the cap (from which you can deduce the approximate assembly date). The code will read "235-YYWWLL 85 C) where 235 is Mallory's EIA code, YY is the two-digit year code, WW is the week of that year, LL is a two-letter code that means something known only to Mallory and 85 C is the temperature rating (Celsius). So you can tell just how old the cap is.

Fender did move up to 40uF for the first filter at some point. You will see Champs with 4x20uF cans where two 20s are paralled, as well as 40-20-20 versions. Since Fender never spent more money on parts than they had to, I assume they had a reason to upgrade to the 40uF main filter. This is a single-ended amp (no push-pull phase cancellation of hum), so it may have had to do with limiting hum in the output. Or they got a deal on a bunch of caps. Who knows.

The amp probably doesn't "need" 40uF, but a 5Y3GT will probably be fine with a 40uF first filter at 320ish volts VAC per plate. The 20uF number we often see is RCA's "typical operation" number. I think Brimar listed 32uF. The issue is the "transient hot switching" current, which can't exceed 2.5 amps per plate for more than 0.2 seconds. With a 60-cycle supply, the cap will be up to 90% of its capacity in less than 0.1 seconds. These were not the most efficient power transformers in the world either, so there is a good amount of impedance in both the primary and secondary windings, which helps protect the rectifier.

[Fender Guy]

Can some one point me to an insulator lol. I see nothing but the actual cap can from the pics I took (and from memory last night looking at it)?

I have a pretty good soldering iron, but not that gun type. It is prob about 30-40 watt w/med tip. I used to build slot cars for my son and went though one iron, and this second one is showing age. It is pretty good, I think I paid like $40-$45 approx. 12-15 years ago. It seems to work for heavy jobs and small jobs like inside a strat as well.

Using those eyelets on BF/SF amps makes me feel like a pro, to me, very easy to get a good soldering connection (as long as you suck the old solder out first). The cap can, I do not think I will have a problem getting it off, not much solder there that I can see (now watch me be wrong). AGAIN, what is this insulator you speak of?

Firestorm..wow...great info, dated my amp to 74, and cap can is also 74, so you guys that said it was orig cap can are correct (and I was wrong).

As far as doing the cap can the right way, I think I have to agree. I do not think I have the heart to just use caps, I will have to find a way to spring for the can. This is my first small amp. I wish I had got into small tube amps a long time ago. The Champ just has a killer tone for home use, which is the only place I play.

Thanks for all the info....

[Firestorm]

You won't need the insulator for a Champ. You see them in Ampegs and other places where the filters are connected in series and you have to keep the negative terminal away from the chassis (since it will have half the B+ on it). But in a Champ you want the ground tabs at ground so you're okay.

You might be able to get the old cap out with any old soldering iron, but you won't be able to make a good ground connection for the new one that way. The chassis is a heck of a good heat sink so you have to get it hot fast. I have a 100-watt gun with a 1/4-inch tip that won't do it. For chassis work I use a 175-watt Weller with a half inch chisel tip. The kind you use to solder pipes.

But if you thought $30 for the cap was pricey, you won't like these: $70 and up. Maybe befriend a plumber

[rp]

My bad, no insulator - duh, it's soldered. Haven't done this in a while, even old champs are now too rich for me. Check out the link to the old post. You can get a big iron or a gun for $50. Iron's better than a gun but both work. Your 40W won't even come close.

[Fender Guy]

Man, you guys bummed me out with the expensive soldering gun. I checked mine, it is Ungar (looks same as Weller) 45 watt.

Glad to have information ahead of time. Would have hated to get in middle of project and find I did not have the right tool.

175 watt..yow

[Firestorm]

It needs a really big tip. Same as some other things.

[C Moore]

I have gotten confused about where you are with the can cap. IF you live near me, IF you need a big iron, I will gladly assist.
Good Luck

[billyz]

Man, you guys bummed me out with the expensive soldering gun. I checked mine, it is Ungar (looks same as Weller) 45 watt.

Glad to have information ahead of time. Would have hated to get in middle of project and find I did not have the right tool.

175 watt..yow

This is what I use and it work great for soldering to the chassis.
http://www.google.com/products/catalog? ... CCsQ8wIwAA#

You don't need 175w, just a big ass tip to get the heat down fast.

[Firestorm]

Looks like that would totally work. And it includes two tips (versatile). Well worth the investment.

[Fender Guy]

Thanks Firestorm, as if I did not feel bad already

Mr. Hand (reminds me of Fast Times At Ridgemont High), thanks but I live in Tennessee

Billy..that looks cheap enough. I have email out to a friend here, he does some house repairs, so maybe he has a hot iron. If not, that link may be an option.



Thanks

[Phil_S]

I checked mine, it is Ungar (looks same as Weller) 45 watt.

I'm pretty sure Weller and Ungar are the same company. I forget who owns who.

[Fender Guy]

I checked mine, it is Ungar (looks same as Weller) 45 watt.

I'm pretty sure Weller and Ungar are the same company. I forget who owns who.

Funny you say that, as I looked up model number on handle and it took me to what looked to be the EXACT same handle, but said Weller. It has been a good gun that is for sure.