Fender Champ Capacitors and other issues

[Paleo Pete]

OK I'm looking around a bit, looking at some 680 ohm 5 watt at a good price, gold band so that should be 5% which I like, do you guys think 5 watt should be heavy enough, or should I hold out for 7 or 10 watt? I think 680 ohm should put me in the right resistance range...

[nickb]

OK I'm looking around a bit, looking at some 680 ohm 5 watt at a good price, gold band so that should be 5% which I like, do you guys think 5 watt should be heavy enough, or should I hold out for 7 or 10 watt? I think 680 ohm should put me in the right resistance range...

5 watt should be fine. You can calculate the power dissipated if you know the voltage across it:
watts = (V^2)/R
I usually at least double that to pick me the power rating of the resistor.

[eschertron]

After what I found here, I can only guess, but I'm thinking it's most likely the cap that's bad... so I'm planning to replace both bypass cap and resistor

If you suspect the bypass cap on the 6L6 tube, simply remove it. [Yes, it will affect the gain, headroom and compression of your signal. So your amp may sound different.] Removing the cap will not hurt the amp physically/electrically in any way, so take it out of the equation while you troubleshoot. JM2C

[Paleo Pete]

nickb - Thanks, I thought maybe 5 watts should be ok but wanted to check with someone who should actually know first. One thing... what is the ^ symbol for? I can handle the rest of that formula, no problem but I'm not familiar with some of the symbols. It's been a long time since high school math class...and I was never great with numbers...but as long as I know what the symbol is for, I can figure it out. The rest is no problem.

eschertron - Thanks for that info. After what I've found out in this thread, yes I do suspect the cap may be bad. I'm almost positive the original resistor was causing trouble, after finding out it was way out of range for what it should be doing, but according to the test procedure I posted above, it points more toward the cap. It's a 50V cap, (and will be replaced with a 100V) so it may be simply not enough to handle it. I'll try the testing you suggested too, and see what happens.

I'm not concerned about it affecting sound, gain, headroom etc, that won't be an issue for testing purposes. Once replaced all that should go back to normal. I'm expecting it to sound slightly different anyway once I get the bypass resistor back into the range it should be. Should still sound good, the amp has always sounded great once I found out and fixed the cap that was causing the bass control to do nothing years ago. (long before any of this happened.) Replaced every cap and most of the resistors, still sounded great. That's the reason I want this little gem fixed...the most awesome sounding practice amp I've ever played.

Thanks a lot guys, still more info to try and digest...but that's ok I want to get a grip on this thing someday...

[nickb]

nickb - Thanks, I thought maybe 5 watts should be ok but wanted to check with someone who should actually know first. One thing... what is the ^ symbol for?

Oh, it means "raised to the power of" i.e. in this case 'Volts squared".

[Enzo]

We have no easy way to type "V squared" on our keyboards, so the up arrow means the next digit is higher up from the line. So V^2 means V squared. Imagine the 2 as above the line.

[Paleo Pete]

Thanks a bunch nick and enzo. I'm not familiar with the way these equations are typed via computer, that symbol threw me. Maybe this time I'll remember to write it down before I log off...

Anyway I tried it last night, with the bypass cap desoldered at one end and taped off to prevent an accidental short. It hummed for 30 seconds and blew a fuse. I'm going to try another 6L6, I also found out the existing one has recently started wobbling, the glass is loose from the base so that may be a huge issue. I only have 1 more fuse, I hope the tube was the reason for blowing fuses...It also made the amp pop when I wiggled it, about 10 seconds before the fuse blew, but no other odd noises. I was checking to be sure all the tubes were well seated, which I'm pretty sure I should have done before I turned it on...yeah I feel like a dummy...I already KNOW to check the damn things and forgot...

I'm planning to order some parts soon, one of my pictures sold recently so I have a few bucks in paypal, and should be able to get the resistor and caps I need. Still no arcing, I think the very old rectifier tube could have been causing the arcing, it hasn't happened again since replacing it, then again I haven't been able to run it longer than a couple of minutes due to blowing fuses, so I'm still not positive. But the new tube sockets are still without arc traces...

[Paleo Pete]

OK Good news...I think...

Just shut the Champ down a few minutes ago, played it with a different power tube (6L6) for about 20-30 minutes. No hum, no blown fuse, didn't seem to sound much different with the bypass cap disconnected.

I still feel like an idiot, I should have spotted the wobbly tube long ago. No excuse...

Anyway it looks like I probably had 2 things going on. The tube was apparently causing the blown fuses, that stopped when I pulled it. The bypass was apparently causing the arcing, unless I didn't run it long enough this morning. Won't really know until I replace it and the other parts (bypass resistor and 350pf cap) then play it for a while and see. I should have those ordered pretty soon, I'm still looking around for good prices. I'm pretty settled on the bypass cap, I found a 25uf 50V Sprague, to replace the 25 - 25 that's in it. The rest is still up in the air, but I'm checking around.

From what I heard a little while ago, I think that may do it. My cat is not happy, she hates it when I pick up a guitar...then she suddenly wants to climb in my lap, rub against the headstock, meows at me soon as I pick it up, obviously fussing...if it's the acoustic...but if it's an electric she runs and hides soon as I turn on the amp...ever try to play guitar with a cat in your lap?

I'll get back in here when I get some parts in and try it out but until then I don't plan to crank it up again. I'd rather have everything right and not take chances.

[Paleo Pete]

Got some interesting info for you guys. Had to do a bit of looking to make sure I was right. If you look in the Accessories folder, then System Tools, Windows has a spiffy little gadget called "Character Map". (Every version since Windows 95, and I think Windows 3.1 too but don't really remember. Linux has it too) Find what you want, click on it, (or double click) click "Select" then "Copy" then you can paste it into a post. So if I want to tell you it gets to 106° here the symbol is there. So why am I telling you this?

W=V²/R

Windows makes the symbol you need available, if you know where to look. I looked for the traditional "divided by" symbol I used in school, didn't find it. It may still be there, I just didn't see it.

According to the voltage readings I got earlier, the wire going to the bypass resistor and cap is getting 18.5 volts. So if I use the 680 ohm resistor I'm planning to get, that formula gets me .503. Half a watt??? OK I'm still going for a 5 watter...just wanted to let you know what I'm getting and see if I'm right.

So anyway, now you know where to find that "Squared" symbol whenever you need it. Loads of others there too, © ® ¼ ½ ± and plenty more. You can also select which font to use, from the drop down box at top, I used the default Times New Roman. Double click automatically copies it to the clipboard. [CTRL + V] is the keyboard shortcut for "Paste" which works great in forum posts, no need to grab for the mouse again, [ALT then TAB] switches between applications, [CTRL +C] Copies...

I've been a computer repair technician for 15 years, I learned a hwole lot about using Windows along the way and I use a lot of those keyboard shortcuts all the time. MOst of my picture editing is done that way. Especially with a laptop, using the mouse (or touchpad) is time consuming and I have to find the damn cursor too...so I just use the keyboard...

OH yeah, feel free to experiment here in this thread if you want to, I won't mind a little off topic nonsense if you want to get the feel of using the Character Map. Might even be good for a laugh or three...

[eschertron]

According to the voltage readings I got earlier, the wire going to the bypass resistor and cap is getting 18.5 volts. So if I use the 680 ohm resistor I'm planning to get, that formula gets me .503. Half a watt??? OK I'm still going for a 5 watter...just wanted to let you know what I'm getting and see if I'm right.

When you sub the 680 Ohm resistor in for the existing resistor (the existing resistor is smaller, right?) then voltage you read across the resistor will go up, and the power it must dissipate will go up ... exponentially. You won't go far wrong with a 5W resistor.

[Paleo Pete]

Thanks, I was wondering but I thought 5 watts should be ok according to previous comments. And yes, the existing resistor is a 510 ohm, so you're right.

I just ordered the following

10 - 680 ohm 5 watt resistors. I'll have spares...the price was good enough to go for it.

5 - 330 pf capacitors. More spares...

1 - 25uF 50V Sprague cap. I found others a bit cheaper, but the Sprague has the best reputation and the ones in my Super Reverb seem to be doing well after 10 years...

Should fix things up as far as I know. Judging by the way it acted when I played it a couple of days ago, it had to be the wobbly tube causing the fuse to blow, that stopped soon as I swapped to a different power tube. I'm not sure if the old rectifier tube or the bypass cap was causing it to arc, but I don't plan to try the old 5y3 till I can find someone with a tube tester. My Triplett needs to be rebuilt before I try to use it. Everything in it is original, I seriously doubt it still works right...I'll probably have questions about that when I get ready to work on it...

[Paleo Pete]

OK. Got all the parts in ans did some solder sniffing last night. Oh boy...

Got it working, ran it a total of about 2 1/2 hours, no arcing, no blown fuse. Played it about 45 minutes at full tilt, sounds pretty good, maybe a little more raunch than before but really not sure, it's been so long since I've had it running.

Checked voltages, everything is low except heater, which is 6.6V. Unusual, that's always been 6.3V. Nothing has been changed but the bypass resistor, it's now the 680 ohm 5 watt I just got, the cap is still 25uF, 50V. The 330pf cap was also replaced with a new one, I added an inch of wire to each lead so I could get it off to the side, out of the heat from the power tube. (also put some heat shrink on it to avoid accidental contact with anything else.) At low volume it sounds a bit more dirty than it should, maybe a bit weak, full tilt it sounds great. Probably breaking up more than it did before, not sure th0ough, I'll have to listen to it some more.

A couple of things worry me. Heater voltage, the whole thing is getting pretty hot, and if I turn the treble knob higher than 5 at full volume it starts to sound garbled and lose power. At 4 it has plenty treble, and sounds great. Also sounds fatter then before when I switch to the neck pickup (I used the Strat in my avatar)

I guess the main thing I'm worried about is the treble response, that never happened before, it always worked perfect, and sounded best at about 7 on the knob, bass on 10. Bass still works great, nothing odd if I change it. Still sounds wimpy with both turned down to nothing, as usual.

I'm going to try and upload a picture showing voltages I got last night, if I can't get the picture to upload I'll put it on Flickr. Last time it gave me problems. Input voltage at the fuse holder was 122.2-122.4. A bit high, but that's what I'm getting out here. Voltage according to the Champ layout in black, current voltage readings in red. Took the picture last night, just before checking voltage. I put bypass cap and resistor up off the board for better heat dissipation, 330pf cap off to the side so maybe it won't catch too much power tube heat. You should be able to get a good look at everything, I've double checked and I don't see any reversed polarity. The only thing changed is the bypass resistor and cap, and 330pf cap. The only one changed in value was the resistor.



Here's the voltage I got originally, before changing anything, I used the Champ layout for this one.



Any questions or input appreciated...I'm not sure if this thing is actually right yet, and the heat and 6.6 heater voltage worry me, as does the treble response. But it sounds pretty good maxed out...

[Paleo Pete]

OK for some reason the Champ layout didn't upload, I'll try again

EDIT - Didn't work again, I put that one on Flickr..and found out why I think...here we go again...

[nickb]

Hey Pete,

That sure looks like a 68 ohms instead of 680 ohms to me in the cathode. That could explain a lot.

[Paleo Pete]

nickb - Yep, you're right. I just spotted that a few minutes ago. Something kept niggling at me and I got out my meter and checked one of them, 68 ohms...I never looked close, and it's wrong. (I had to get out my cheat sheet) but if I"m not badly mistaken, 680 should be blue, grey BROWN...this one is black, so x1 not x10. I'll be contacting the seller shortly. Just wanted to check in here and see if anyone had spotted it yet.

One good thing though, I Just played it for about 30 minutes, sounds pretty good actually, except that it seems like it has too much gain, but heat didn't seem near as bad. I think what happened last night is I Had it leaned against the back of a chair so it was tilted upwards, and that was causing it to hold in a lot of heat. This time, standing upright, it didn't get too hot at all, the chassis was barely warm right beside the power tube as it usually is. So I think the heat was my fault and doesn't seem to be an issue. I also had it laying flat face down to check voltage, with the chassis lying in the back of the case, I'm sure that held a lot of heat in too. It fits well and puts it in a good position to check voltage, tubes don't touch anything...So everything I did last night contributed to high heat. Today it seemed much more normal.

I think I'll put the 510 ohm back in a s a temporary measure, I don't think 68 should be in there at all...and see what I can work out with the seller, I have 10 of these things that I now don't need...