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Topic: Question about replacing Electrolytic Caps |
Frank James Pracher
From:
Michigan, USA
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Posted 10 Sep 2014 11:30 am |
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I picked up a 1949 Oahu Tonemaster 230k recently. People keep telling me I need replace all the electrolytic capacitors, but this thing works great. It doesn't have any more hum than my relatively new Blues Jr. does.
Is this a must?
At some point the cap can may have been replaced as the values don't match up perfectly with the schematic, although it could be original
I have the parts, and I can do the work myself but I'm firm believer in "if it aint broke......."
There are cats on here who have forgotten more about tube stuff than I'll ever know so I await your wisdom!
_________________
"Don't be mad honey, but I bought another one" |
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Tim Marcus
From:
San Francisco, CA
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Posted 10 Sep 2014 12:24 pm
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if it works, don't mess with it
_________________
Milkmansound.com |
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Bill A. Moore
From:
Silver City, New Mexico, USA
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Posted 10 Sep 2014 3:53 pm
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| I have a mid 60's Airline with the original cap can, that works great. I do use it at least monthly to try to keep the caps formed. (I think the cans are more robust than the individual caps.) |
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Blake Hawkins
From:
Florida
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Posted 10 Sep 2014 9:48 pm
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Some electrolytic caps will last a very long time.
I have 1950's radios with the original filters that are still fine.
You are correct to run the amp every so often to keep the caps formed.
The coupling and bypass caps will usually increase in capacity and develop leakage over time. You may not notice the change as it is very gradual.
I agree with Tim, as long as the amp is performing
well and you like the tone, just leave it alone.
If it has a fuse, I'd check that to make sure it is the right value. |
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Hamilton Barnard
From:
Oro Valley, Arizona (deceased)
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Posted 11 Sep 2014 9:18 am
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| I have MANY old Marshalls, including original plexis. Filter cans get changed only when absolutely necessary. |
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Timothy Foster
From:
New Jersey, USA
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Posted 11 Sep 2014 10:56 am
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| Hamilton Barnard wrote: |
| I have MANY old Marshalls, including original plexis. Filter cans get changed only when absolutely necessary. |
Agreed! At one point I had two blackface Fender Princeton (non-reverb) amps -- a '64 and '65. I used them a lot for recording, so I was pretty familiar with the nuances of how they sounded... I decided to recap the '64, remove the feedback loop, upgrade to grounded AC plug, etc... Ya know - loved the amp and figured I'd love it even more!
Bottom line is, it was never quite the same, even after returning the feedback loop to it's stock form. Something about those old caps -- I guess the random fashion in which they had aged and fell out of tolerance -- was part of the magic in this particular case. And now it was gone, replaced with a much less interesting, slightly louder and "stiffer" tone...
So... I sold it on ebay and kept the '65. And I ain't touching it! |
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Frank James Pracher
From:
Michigan, USA
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Posted 11 Sep 2014 11:20 am
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Sounds like a consensus!
_________________
"Don't be mad honey, but I bought another one" |
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Paul Sutherland
From:
Placerville, California
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Posted 11 Sep 2014 11:47 am
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I just purchased a 1971 Twin Reverb. The low end would break up and sounded flabby. I took it to a reputable amp guy in my area and he determined the caps were original and recommended they all be replaced. I just got the amp back after the cap job was completed. I will use it tonight on stage for the first time. At home, the amp sounds vastly better with the new caps. I have a series of gigs this weekend so will report back.
I suspect that sometimes new caps are a good thing. Maybe not always. I'm no expert on electronics. Just my 2 cents.
_________________
It don't mean a thing if it ain't got that swing. |
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Jeff Porter
From:
Stumptown, OR, USA
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Posted 11 Sep 2014 2:19 pm
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I have a 67 Vibrolux that I've played for years and I liked it, but never really loved it. Decided to try new filter caps and it made a huge difference. Tightened up the bass and mids. I love it now.
Whenever I work on my older amps I always measure the part I am replacing as well as the new part, replace them one at a time, and then listen after the replacement. I can always put the original part back in if it's not an improvement.
And since it hasn't been covered yet in this thread..... if you don't understand how to discharge capacitors then please seek out a qualified tech. Amplifiers can hold lethal charges even when they have been unplugged for a while.
_________________
"I make dozens of dollars a year playing music." |
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Bill A. Moore
From:
Silver City, New Mexico, USA
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Posted 11 Sep 2014 4:04 pm
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This is a pet peeve of mine, as soon as anyone talks about changing a filter cap, someone pipes up about lethal voltages. (The amplifier manufacturers have to label the chassis as such for insurance purposes). They could have a lethal voltage if there was a way to directly send the very, very low amperage, high voltage charge to your heart. I have been shocked many times, both from electronics, and automotive ignition systems. (Automotive systems can be more than 100K volts!)
There is no documented incidence of anyone being killed by the high voltage produced in guitar amplifiers. There are reports of guitarists being hurt, and killed, from mains voltage across their guitar strings due to faulty mains wiring, (improper grounding).
You will hurt yourself more from the reaction to the shock, than from the actual zolt. |
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Blake Hawkins
From:
Florida
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Posted 11 Sep 2014 5:13 pm
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Please forgive some additional information on the high voltage. I'm another old technician who has been working on high voltage radio, television, and electronic gear since 1949.
You can get away with a lot, and I've been hit a number of times when I was younger. Sometimes I got a burn, sometimes my heart rate went way up and I had to lie down for a while.
What can kill you is the current.
All well designed power supplies include a bleeder resistor across the power supply to discharge the
caps when power is removed.
Most of the time it works, but if it fails then the caps can hold a charge.
Bottom line is why take the chance? When you go into a device to repair it, you don't know what has failed.
It only takes a few moments to make sure that the caps are discharged.
For amps I have a resistor with clip leads that I touch to each of the filter caps.
Normally a cap in an amp won't kill a healthy person.
You don't know how sensitive your body is nor the path the current is likely to take.
Again, why take the chance?
Just my $.02. |
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Frank James Pracher
From:
Michigan, USA
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Posted 11 Sep 2014 5:16 pm
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I have no complaints with the amps sound now, so I think I'll leave them be. People kept telling me I HAD to change them on an amp this old.
Regarding safety, I worked in electronics repair for a few years. (Some high voltage stuff, but no tube amps), and I'm a ham radio operator. So I know to discharge the caps and what not.
The first thing I did was put a grounded cord on the amp.
_________________
"Don't be mad honey, but I bought another one" |
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Michael Hartz
From:
Decorah, Iowa, USA
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Posted 14 Sep 2014 3:28 pm
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| Had a 76 Session 400 that I did my own cap job on per Brad Sarno's Session 400 website so that I could sell the amp. Afterwards it sounded soooooooo good I couldn't bear to get rid of it. |
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John Billings
From:
Ohio, USA
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Posted 14 Sep 2014 6:27 pm
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"All well designed power supplies include a bleeder resistor across the power supply to discharge the
caps when power is removed. "
Assuming no dumb assembly errors! Which I was once guilty of. Worked for a small company that made club lighting, including strobe lights. Our big strobe used the landing strobe for 747s. There were two, oil-filled can caps, 660 volts on reach chassis. The easiest way to move them off the assembly bench was to grab the two cans. I forgot to put the bleeder circuit in one. Grabbed the cans, and received a jolt that made me see the blue light! All my muscles spasmed, and I threw the chassis into the wall so hard I bent it at about 40 degrees! Had a headache for a day! Shocks never bothered me after that. I could lick my finger and touch a wire and determine if it was the hot 120 wire. Built a 500,000 volt Van de Graff generator in the 7th grade, and that started my shocking experiences! No amperage to speak of with that though. I've become much more careful as I've aged though! Don't take chances! Discharge those caps! |
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Craig Baker
From:
Eatonton, Georgia, USA - R.I.P.
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Posted 14 Sep 2014 8:31 pm
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Josh,
Interesting story. The other problem that pops up is when a bleeder fails open and the poor engineer asumes it's still doing its job.
Wonder how many million science fair students built a Van de Graff generator?
Didn't Buddy Charleton record a song called "Almost To Tesla"?
Best regards Josh, and keep the grounding stick handy.
Craig Baker 706-485-8792
cmbakerelectronics@gmail.com
C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024
_________________
"Make America Great Again". . . The Only Country With Dream After Its Name. |
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John Billings
From:
Ohio, USA
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Posted 14 Sep 2014 8:35 pm
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"Wonder how many million science fair students built a Van de Graff generator? "
Lots, fur shure! Plans were in the monthly mag, Science Experimenter. The hardest part to get was the plexi tube. |
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Tommy Mc
From:
Middlesex VT
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Posted 15 Sep 2014 3:55 pm
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| On virtually every website dedicated to vintage tube amps, the stock advice is to replace old filter caps. The word is that they deteriorate with age, and if they fail, they can do serious damage to the amp. Is this true, or just a myth that's been repeated and passed on? |
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Craig Baker
From:
Eatonton, Georgia, USA - R.I.P.
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Posted 15 Sep 2014 4:20 pm
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Tommy,
If the electrolytic caps in the power supply section short, they can quickly destroy the diodes or rectifier tube and possibly take the power transformer out also. However the proper fuse should protect these components. Depending on where the capacitor is used in the circuit, it may do much less damage, or none at all. For example, if a coupling capacitor opens, it probably will do no damage, but the circuit will simply stop functioning.
Craig
_________________
"Make America Great Again". . . The Only Country With Dream After Its Name. |
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Tommy Mc
From:
Middlesex VT
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Posted 16 Sep 2014 6:34 am
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| Thanks for clarifying that Craig. My understanding is that the electrolytic caps in the power supply section don't have any effect on the tone...other than quieting the background noise a little. If this is true, then it *does* make sense to replace them before they fail in a vintage amp...doesn't it? |
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Craig Baker
From:
Eatonton, Georgia, USA - R.I.P.
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Posted 16 Sep 2014 7:13 am
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Tommy,
The caps in the power supply will indeed effect the overall sound of the amp. Properly working caps "stiffen" and help to regulate the power supply preventing the voltage from dropping suddenly when the current demand is higher. (when the music is played louder.) This helps eliminate distortion at high volume. Nothing beats having the right parts for the job.
Craig
_________________
"Make America Great Again". . . The Only Country With Dream After Its Name. |
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 16 Sep 2014 6:56 pm
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If the filter caps are bad you can have 'ghost' tones affect your sound... hum as well. In most amps the power supply hum is balanced out in the final section... but the preamp section can still be affected. You want good filter caps in there for sure.
_________________
Too much junk to list... always getting more. |
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Tommy Mc
From:
Middlesex VT
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Posted 17 Sep 2014 2:32 am
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| Craig Baker wrote: |
Tommy,
The caps in the power supply will indeed effect the overall sound of the amp.
Craig |
I stand corrected. Still, Frank (the original poster) inquired about replacing the caps in his vintage 1949 amp. The consensus here seems to be "if it ain't broke..." which flies in the face of everything I've read in the vintage amp forums....and the advice Frank was getting from his friends. Not being an expert, I've blindly followed this advice too....replacing the original caps in the power section of my vintage amps. Have I, (we) been misled by oft repeated misinformation, or is it really the safer way to go? |
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Craig Baker
From:
Eatonton, Georgia, USA - R.I.P.
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Posted 17 Sep 2014 4:07 am
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Tommy,
All kinds of forums are made-up of well-meaning folks who often pass along the incorrect mis-information that they have received. Probably many industries are full of people who were taught how to do it wrong by someone else who was taught how to do it wrong by someone else who was . . .
However, there are a few out there who do know the theory. For example, we may approach things from a different angle, but I have never seen incorrect advice from Stephen, Brad Sarno or Tim Marcus. As for me, I'm not sure I replace all of the caps if the amp is working properly, but I would certainly make sure it has the correct fuse.
Best regards,
Craig Baker 706-485-8792
cmbakerelectronics@gmail.com
C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024
_________________
"Make America Great Again". . . The Only Country With Dream After Its Name. |
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John Limbach
From:
Billings, Montana, USA
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Posted 17 Sep 2014 5:31 am
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I've been around electronics for a long, long time, both as a professional early in life and a ham radio operator (K8NN) since 1971. Like everyone else, I have opinions.
Regarding electrolytic caps, particularly power supply caps, my experience has led me to the following conclusion:
50+ year old power supply caps are a disaster waiting to happen. Like gear up landings (you fellow pilots will vouch for this), it's not a question of "if" but "when".
Follow your heart, but as for me, that's the first step in any vintage amp project. Well, maybe second if it has a death cap! |
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Blake Hawkins
From:
Florida
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Posted 17 Sep 2014 6:35 am
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It is one thing to discuss "what if" regarding the Electrolytic caps.
However "Good Practice" is something else.
If I restore an older amp and have to guarantee it,
I will replace all the electrolytic caps, all the coupling caps and check the values of every resistor. There are also other things to do to ensure performance and longevity of the amp.
I agree with Craig, Tim, John, and Brad.
An amp that has been in a closet for 25 to 50 years
should have the caps replaced.
The amp will run for a while, but the stress on the old parts will eventually cause them to fail. |
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