#1
Hey all,

I have a 1979 Fender Bassman 100 with original filter caps, and I have a few questions...

I'm looking at getting F&T caps because they're very inexpensive compared to Sprague ($37 cheaper, actually) and some people say they're better. Unfortunately, I cannot get a 20uF at 500V cap through F&T, but I can get a 22uF at 500V. Would this be an issue? (I'm fairly certain it's not, but I would like a definitive answer)

Besides the filter caps, what other caps inside of this amp are electrolytic? As far as I know, majority of the caps are original.

I have no outstanding issues with the amp besides an occasional oscillating interference-like noise that comes and goes. I'm pretty sure it's tube/socket related because after I push the tubes back up into their sockets, it goes away.

When that noise isn't present, the amp idles very quietly. I almost can't tell that it's on standing 10 feet away. I mention this noise only as a reference to other capacitor-related issues.

Here's a picture of the whole inside:


Here's an album of more pictures:
http://s37.photobucket.com/user/Nicholas_Culliton/library/Bassman%20100%20gut%20shots?sort=3&page=1

Thanks for the help!
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#2
F&T are very good. 22 uF is fine. Seeing as how it has a SS rectifier, you could go substantially higher if you wanted to.
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Cathbard Amplification
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#3
Thanks, Cath!

On the gut shot, are the white caps also electrolytic ones?
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#4
Yeah, those look quite new though.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
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Fender 5F1 Champ clone
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Cathbard Amplification
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#6
They could be newer than 1979, but I'm fairly certain that they are original because all of the gut shots I've seen of Bassman 100s have those same exact caps or newer ones. I also can't find all the exact values, like the 80uF @ 75V or 5uF @ 50V.

What would be a good replacement if I can't find a 5uF @ 50V cap? I know the 100uF @ 100V is fine for the 80uF @ 75V cap.
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
Last edited by nick.culliton at Jun 17, 2015,
#9
I don't think Id bother with anything other than the power supply caps for now.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#10
I would really like to get it done in one go. The 25uF @ 25V and 5uF @ 50V caps on the left look eerily new, so I suppose I can leave them be. Would it make sense to do the two 80uF @ 75V caps on the right, then?
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#11
Do 'em if you like. If they look old, replace them.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#12
If I were to replace the 5uF @ 50Vs, what would be a good replacement for them? The closest I can find is a 4.7uF @ 50V. I'm pretty sure I'll just do the ones on the left side later because I would have to order the two 5uF @ 50V replacements separately.

The 7 F&T caps I have in my cart (5 filter caps, 2 bypass cathode caps) come to a whopping $36.50. That's half as much as Sprague Atoms!
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#13
4.7 is fine. 10% = 0. Stick with F&T.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#15
Sprague Atoms will be cheap enough at those values. Go for those.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#16
Well, I paid $45.54 for all 10 capacitors. I had to order the 5uF @ 50V caps from a different store. The caps on the left will be Sprague Atoms and the caps on the left and filter caps will be F&Ts. Pretty stoked to be doing this myself and for way less than I thought it was going to be.
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#17
Now don't forget to discharge the big caps before you touch them, won't you?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#18
I was just joking about that.

Yep! I don't need a special kind of cable to do that, do I? I have alligator clip cables galore that I can use.

Also, to test that they're drained, can I use a multimeter?
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#19
If they are fully charged, using a wire can result in it welding into place. So don't use the alligator clip unless you have a resistor (say, 1K) in series with it. Otherwise just use plain wire because you are going to toss the cap away anyway.
Yes you can use a volt meter if you are worried but shorting it out will discharge it.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#20
Can I partially drain them if I flip the amp on and then turn it off without turning standby on? I just want to use the voltmeter to make sure I'm touching the wire to the right place to drain the cap.
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#21
Not really. Just short out the two leads on the cap and you'll be fine.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#23
It'll be obvious once you're looking at them.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#24
OK...all those are original caps. My Super Reverb had the same white electrolytics in it. Any time you replace caps, all you have to remember is stay within 10% of the original capacitance. I had the same issue, most standard cap values have changed, it's not easy to find a 50uF any more, 47 uF has to do.

Another thing to remember, the voltage listed on a capacitor is the maximum it can handle, not a requirement. So if the original is a 50uF - 50V, the circuit might only be using 30V at that point, that's fine because 50V is the max it can handle. So you can use a higher voltage rating with no problems, but the capacitance (uF) must be within 10%. Do not use a lower voltage rating. a 25V cap will not work in a 50V application.

The blue ones like the very first one on the left are the standard ones Fender used, generally the cheapest they could find. I replaced them with new Sprague "orange drops". Some were blue, some were brown.

Watch the polarity. I usually remove one end only, solder that end of the new one in, then remove and solder the other end, to be absolutely sure I don't mix up polarity.

To discharge the caps it's best to use a wire with a resistor, place it across the filter caps. Leave it in place while working on it, they can still build up a low level charge. You can also turn the amp on and unplug it while playing the guitar. Don't stop playing, let a note sustain and pull the power plug. It will keep making sound until the caps are drained. Not extremely reliable, but it does work. My Super Reverb is designed so that when you shut it off, it drains itself, yours might be too. I didn't know that, found out when asking some questions on an amp electronics forum.

If you turn the amp on at all, you will fully charge the caps. Stand by or not...it takes a couple of seconds at most, the warm up time is for tubes to heat up, not caps. They charge almost instantly whether it's on standby or not. The standby switch lets tubes heat up without getting full power to the rest of the circuit .

Yes a multimeter will tell you if you have any left over charge. Keep it connected for a couple of minutes and it will slowly drain a low level charge, but don't bother if you're showing 300V, it will take a couple of hours...as in 10 to 15 minutes to drain just 1 or 2 volts...

The filter caps have a lead on each end of the cap. Short them with a wire to each end. One should be marked + or - for polarity. Be very careful to keep that the same. I think, not positive, but I think you can clip the wire to the chassis and the other end to a positive terminal to drain them. The resistor keeps it from welding itself in place, use at least 1K as already noted. Just solder it into the middle of a jumper wire. Definitely use alligator clips with rubber boots...DO NOT touch anything bare metal while discharging caps...that's why an alligator clip is actually a good idea, clip it to one end, hold the other (rubber booted) clip, keep your other hand IN YOUR BACK POCKET and discharge the cap. It's that dangerous in there, silly sounding, but very serious, precautions are the only thing that will keep you alive to tell the story. Those caps hold up to 500V, it will throw you across the room and at least put you in the hospital.

I'm not all that good with amps, but I've rebuilt my Champ and Super Reverb, including complete cap jobs, and modified a Peavey Classic 30. No such thing as being too careful about the high voltage inside there.
Hmmm...I wonder what this button does...
#25
The tubes stop conducting at around 100V or as soon as the cathode begins to cool because the heater is off. Don't expect the charge to be gone because it makes no sound.

For signal caps - Russian military stuff off ebay is the go. Cheaper and better than Orange Drops. And LOTS cheaper.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#26
@Paleo Pete
I was able to find a 5uF 50V, but the closest I could find to 80uF 75V was 100uF 100V, which appears to be a popular 80uF 75V replacement. It's within 20% capacitance, and I should not notice a huge difference, at least according to other people on the internet.

I plan on taking a picture of the caps before I take them out. I figure I will drain and clip them all out just to be safe so that I don't end up forgetting to drain one or something stupid.

@Cathbard
Do I need to be concerned about replacing signal caps? Only if they're broken, right?
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#27
Yeah, signal caps last forever. Test 'em before you bother.

100 uF will be fine. Bigger is good - less ripple. They fit the smallest ones they can get away with to save money. Tube rectifiers limit the size of the first cap - but your SF has a SS rectifier so you can go substantially higher if you wanted to.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#28
Great! I went to the surplus store today and made some 1k ohm resistor wires. I tested them and they check out.

Monday all the caps are supposed to be here. Thanks for all the assistance and advice. One more question, can I test a capacitor without using a capacitance meter? If I can use a multimeter or voltmeter that would be pretty cool...
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#29
You can test for DC shorts. That isn't going to tell you a lot though. RLC meters can be bought very cheaply on ebay these days though. Buy one.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#30
Well, the recapping was a success! Turns out that one of the filter caps was ruptured. I haven't played on it extensively yet, but it seems louder and cleaner at high volume and idle even quieter.

For a few weeks, it has been breaking up quite a bit while cranked for shows/practice. I cranked it up louder than I would for a show or practice and it did not break up.

The weird, oscillating sound appears to have gone away too.

In addition to the recapping, I used contact cleaner on the sockets (not directly in the sockets), so maybe that also fixed the breakup issue and weird sound. Pretty happy to have done it all by myself with the help of Cath, schematics and other internet resources. Cath, I'd send you a thank you card, but I think postage alone would be about $5.

Thanks!
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#31
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band