Filter Caps/Cans- Important ? You Bet! Pt.#2

toneman · Post by **toneman** » Tue Aug 26, 2003 6:54 am

Here's a little experience that I'd like to share with you on what happens if you leave the old original cans/caps in your amp..
A few years back Guitar Center Hollywood asked me to look at an amp for one of their customers. It was a `67 or `68 era Marshall 100 watt plexi. The amp didn't sound right and the volume kept dropping. The amp had all of it's six original filter cans still in the chassis. Two of them were reading dead shorted on my meter. These two were tied directly to the center tap for the output transformer and supplied voltage to that section. The amp had not even been turned on in a number of years. The amp sounded fine for about 20 minutes according to the customer after he had gotten it home(he didn't have much of a chance to play it in the store..) and then slowly started to go south..What happened? Well as the cans started to warmup as the amp warmed up the electrolyte solution had crytalized & shorted out the two cans rendering them really non-exsistant. This slowly caused the output tranny to short itself out internally on the primary side(or the side with the high voltage-around 550 volts on this amp). The end result was a great old amp with a toasted output tranny. The amp needed the output tranny rewound(about $300.00) and a whole set of filter cans.
G.C. could have had the filters replaced when they knew somebody was interested in the amp and saved themselves alot of money and embarassment. A can/cap job on this amp would have run them around $140. Instead they spent $440. to make the amp right for the customer.
Now.. Filters act like a battery and can store leathal amounts of voltages. If you do not have any amp or electronic experience then leave this stuff to a pro!! I certainly don't want to hear someone here has electrocuted themselves by playing around in their amp. Best way to work on an amp though is with ONLY one hand! Your body will act as a conductor with voltages trying to go from postive to negative D.C. in an amp. I can't stress this enough.. "The voltages inside your tube guitar amp can and will kill you"!!! Got your attention? Good!

rictified · Post by **rictified** » Tue Aug 26, 2003 8:45 am

I'm having the filter caps replaced in an old SVT head right now, the tech is having a hard time finding them.
I went to tech school 20 years ago but never really did much with it except fix my amps and antique radios, but I didn't want to fool around with that. I forgot about the old adage of using only one hand, my old teacher used to stress that also.

bassman · Post by **bassman** » Tue Aug 26, 2003 9:26 am

Are there Filter Caps in Solid State amps? Like the Thomas Organ Vox amps of the mid to late 60's?
If so, do the same rules apply?

dougp · Post by **dougp** » Tue Aug 26, 2003 11:19 am

Jon - yes, this goes for pretty much all electronics. The last time I had my Vox Jaguar (organ) serviced, I had the original 60's electrolytic capacitors replaced.

soundmasterg · Post by **soundmasterg** » Tue Aug 26, 2003 10:40 pm

Hi Bob. You'll probably have to have your tech sub in different values of caps in that SVT. Since modern caps are much smaller for a given value, sometimes people will gut the inside of the can caps, and stick in a modern replacement inside the old can cap, so it still looks original.
I look at electrolytic caps as the same thing as spark plugs on a car, and so I don't have any qualms about replacing them with something different if I can't find the original value. Besides, radial electrolytic caps are WAY cheaper nowadays than can caps due to their use by the computer industry, and they are also a lot smaller so you can double up caps to reach a given value if you need to pretty easily.

Another problem with the can caps is that they all share a common ground point for a multisection can cap, and if hooked up to different sections of the amp, can cause ground loops and more hum than what you would have if you used seperate caps and ground them seperately too. If you're interested in it, Kevin O' Connor's series of books are great reads on amp maintenence and repair/design.
And lastly, I don't blame you for not wanting to mess with your SVT yourself. I haven't done that yet either on mine. Too high of a voltage for my bones! I do enjoy playing with my Sunn 2000S though! Its got lots of room and lower voltages to boot...

toneman · Post by **toneman** » Wed Aug 27, 2003 9:09 am

Hi guys; Yes, all electronic audio amps/preamps and even some effects pedals have electrolytic caps. Even the old Thomas Organ Vox stuff and all other solid state guitar amps need the electrolytics replaced on a regular basis just like the tube ones. This also holds true for vintage tube or solid state HiFi amps. I have three old early to mid sixties Fisher tube stereos and all of them have had every electrolytic cap in them replaced. Makes a big sonic improvement.
I just finished an SVT last week. I can get pretty close with the filtercans and cap values as alot of stuff is available thru Antique Electronic Supply or their parent company CE Distribution. They have alot of newly manufactured multi-section filter cans(like 100uf x 100uf @ 600v). I buy the majority of my caps and cans from them. One thing I'd like to make clear though... buying NOS tubes is great as tubes don't age unless they are plugged in an amp and used. However.. This does NOT hold true for electrolytic caps or cans. Never, ever buy any NOS electrolytic caps! Now though, NOS coupling and/ or tone caps do not age or become de-graded if un-used. Also, solid state amps operate at much lower B+ supply voltages than tube amps. typically a solid state amp runs anywhere from 20 volts up to maybe a 100 volts internally. Most tube amps need to run from say 300 volts up to 500 volts depending on the design and output level requirements.
Here's a few common amps and their average voltage(B+) supplies.
Vox AC-15 & 30: 350 volts D.C.
Vox AC-50 & 100: 500 volts
Fender Deluxe: between 380-450v (depending on era)
Fender Bandmaster's, Bassman's, Pro's: 450v
Marshall JTM-45's, plexi 50 watters: 450v
JMP 100's, 1959's etc: 500v-600v
These are all average voltages for these amps. Depending on the era, the voltages can be a bit higher or lower.

rictified · Post by **rictified** » Wed Aug 27, 2003 9:20 am

That's probably the problem Greg, he asked me if I wanted him to get the original cans back in it, and I said yeah, (you never know it might be in BassPlayer as amp of the year someday LOL). I'm going to be here in Perú for a year anyway, so that should give him plenty of time.
I had a Sunn 2000S and sold it for peanuts years ago like an idiot. I had two of the 2000S cabs too, with JBL D140's in them. I had these at different times though, I used the cabs with a Marshall Major head.
I've actually done simple things to the SVT like change the resistors when I was too late in changing power tubes, I also converted an old head to 12AX7's from 12DW7's which I don't recommend, it lost a lot of gain. But I wouldn't want to fool around with the power supply.
My present one has 12DW7's in it.
I also have one of those ST.Louis Music hand made special run heads made in 1987, it has 12AX7's in it, but it is a great sounding head, very reliable too.

mortivan · Post by **mortivan** » Wed Aug 27, 2003 1:05 pm

Interesting posts. Thanks Don.

soundmasterg · Post by **soundmasterg** » Thu Aug 28, 2003 1:11 am

Hi Bob. Sounds like you've had a chance to try quite a lot of stuff out. I used to have a mint 200S with 2x15 200S cab with the 2 JBL D140's in it and I got rid of it to get the SVT. I wish I wouldn't have now, but too late! So I scored a nice 2000S for a good price a couple months back. I still need to locate a good old 2000S cabinet with the D140's in it, or get some D140's and have a Sunn cabinet made. I'm in the Portland Oregon area, and Norm Sundholm from Sunn is still in the area, so that may be an avenue to go if I can only find some good JBL's.
I think since my SVT is from the MTI era, it has the 12ax7 in it instead of the 12DW7, but to be honest, I haven't looked. I haven't had to go inside it yet. I have read that the components in it are cheaper and not quite the same as the American made ones. Mine is made in Japan in the early 80's.

Don, have you had any problems with too much hum from using the CE series multi-section caps from AES? Some of the people on Ampage and the Weber board were talking about bad 20/20/20/20 450v caps from AES. They would work but they hummed a lot worse than the old ones. They were theorizing that the sections inside the cap can had bad grounding or something like that.
I read most of the books and most people seem to suggest using radial lead caps as they are smaller and cheaper and offer better grounding options since you can ground each stage seperately from each other. Of course if you are trying to be original, then you have to use the cans I suppose...
It would be cool to have your knowledge of what voltages all the amps typically use Don! I haven't messed with enough amps to have that knowledge built up yet!

rictified · Post by **rictified** » Thu Aug 28, 2003 10:00 am

Greg does your SVT sound the same as the others? There is a few pages in the Ampeg book on MTI SVT's, I've never tried one before. I think it does have 12AX7's, I'd be interested to know.
The Sunns were nice, but I think you made a good decision getting the SVT, I would just want my old Sunn to collect it.
Yes, I've had a lot of stuff over the years that I sold, like nice old Fender bassmans, and Dual Showmans, the Sunns, Marshalls, I had an orange Marshall Super Lead head, other Ampegs, like V4B's, B-15's, I'm crying now,LOL
The book says that the bass player from AC DC prefers the MTI SVT's over any other.
Also if yours is an early one, supposedly it was built with mostly old Ampeg parts from Magnavox who owned the company for a long time (and ran it into the ground almost)

soundmasterg · Post by **soundmasterg** » Fri Aug 29, 2003 2:37 am

Bob, I've never played a real Ampeg or Magnavox era SVT, so I can't tell you if the MTI does sound different or not. I do believe it does have the 12ax7 though. I have heard that about AC/DC. I'll have to check to see if it is an early MTI or not. If I remember right from reading in the Ampeg book, there wasn't any good way to tell its exact date.
I have great memories of my Sunn 200S and 2x15 cab with my Rick bass. If I can get the 2000S to sound anywhere close I'll be VERY happy. It does not sound right at all thru the SVT cabinet though. I could use both the Sunn and the SVT with a stereo setup and be like Geddy Lee! Ha! Ya right....

toneman · Post by **toneman** » Fri Aug 29, 2003 7:59 am

the CE filter Cans that I've used have worked just fine. I haven't had any hum or noise problems with them at all. Maybe the early runs had some problems but the one's I've used over the last year have been fine. I've ever got some in my old Fisher's.

soundmasterg · Post by **soundmasterg** » Sat Aug 30, 2003 12:43 am

Well maybe they had a couple runs that were bad then Don? I got the info about them possibly being bad recently(within the last couple months) from some boutique amp manufacturers on the weberbbs and ampage. I can't recall which guys were saying they had had problems with them right now however. Of course, since its hum we're talking about here, since everyone hears differently, maybe some of these people may be used to the hum of old amps or not, its hard to draw the line at where a problem would be. I hope they work well as I have one I haven't tried in an amp yet that I got a couple months ago!

rictified · Post by **rictified** » Mon Sep 01, 2003 8:33 am

If I remember correctly the thing I didn't like about the 2000S was that the tone controls didn't do a hell of a lot, neither did the Marshall Major tones (voiced for guitar Don?) When I got my first SVT I was amazed (and a little intimidated) at the range of the tone controls and the bewildering array of switches. It took me a little while to get used to them, but I wouldn't use anything else now but an SVT, or at least an Ampeg. Even though there are some nice amps around nowadays, nothing sounds like an SVT to me.

toneman · Post by **toneman** » Fri Sep 05, 2003 7:06 am

Bob; You're right about the 2000S's. Controls do very little. The first Marshall Major is voiced for guitar but since it had alot power was soon adopted by bass players in the U.K. There are two preamp version's although you don't really see many of them as they didn't make all that many and were only available between 1967 till 1974. Marshall also made a PA head version but discontinuted those in `71. The thing that most people didn't care for was the active tone controls.