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westtexasred
Shortscale Cultural Minister
Joined: 26 Apr 2006
Posts: 16610
Location: Minneapolis
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 Posted: Tue Jan 28, 2020 6:47 pm Post subject: Do old amps have to be recapped? |
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I found this 1964 National Westwood amp in my girlfriends basement.I took it to a local guitar shop and they cleaned up put on a new power cord and reverb tank because the old one was "dead". They said the caps were ok but when I have posted on some other forums some people say it should be recapped because it is 56 years old. Is my amp going to catch on fire and burn down the house if I don't change them? Also can the old "Shoebox Reverb" be brought back to life?
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Nick
Y'SEE!?
Joined: 20 Apr 2006
Posts: 8603
Location: Albany, NY
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| Posted: Tue Jan 28, 2020 7:40 pm Post subject: |
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Only if they’re damaged or leaking, unless you’re into preventative maintenance. If it doesn’t sound broke, I wouldn’t fix it.
I would think the shop would have checked it over for leaky caps when they were diagnosing it. |
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westtexasred
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Joined: 26 Apr 2006
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Location: Minneapolis
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| Posted: Tue Jan 28, 2020 8:10 pm Post subject: |
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| Ok thanks! |
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Fakir Mustache
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Joined: 25 Sep 2013
Posts: 4111
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| Posted: Tue Jan 28, 2020 8:27 pm Post subject: |
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You won't get full power, it will be like 30 microfarad caps putting out 10. There are certain ways to measure caps.
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holyCATS1415
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Joined: 24 Apr 2008
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Location: PDX
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| Posted: Tue Jan 28, 2020 8:36 pm Post subject: |
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Really cool find! Those old national / valco amps are great.
It’s not a bad idea to have the caps replaced, but if it’s running fine and isn’t making any weird noises I wouldn’t worry about it.
You should be able to tell if they are going bad just by looking at them. Weird waxy gunk will be leaking out. Don’t touch them though! They have high DC voltage stored in them. |
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westtexasred
Shortscale Cultural Minister
Joined: 26 Apr 2006
Posts: 16610
Location: Minneapolis
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| Posted: Tue Jan 28, 2020 10:36 pm Post subject: |
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| holyCATS1415 wrote: |
Really cool find! Those old national / valco amps are great.
It’s not a bad idea to have the caps replaced, but if it’s running fine and isn’t making any weird noises I wouldn’t worry about it.
You should be able to tell if they are going bad just by looking at them. Weird waxy gunk will be leaking out. Don’t touch them though! They have high DC voltage stored in them. |
Ok,thanks man! |
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sunshiner
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Joined: 02 Nov 2012
Posts: 4945
Location: Around the corner
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| Posted: Wed Jan 29, 2020 4:44 am Post subject: |
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Electrolytes dry up with the time and usually explode. Sometimes, but not often, they catch on fire, considering that amp is built from wood, yes it is advisable to replace them.
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Nick
Y'SEE!?
Joined: 20 Apr 2006
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Location: Albany, NY
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| Posted: Wed Jan 29, 2020 12:11 pm Post subject: |
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| sunshiner wrote: |
| Electrolytes dry up with the time and usually explode. Sometimes, but not often, they catch on fire, considering that amp is built from wood, yes it is advisable to replace them. |
have you ever seen or heard of an amp catching fire due to old caps?
You can usually hear a bad cap in an audio circuit, or see the vents swelling or electrolytes leaking on the board. Several local shops in my town specialize in vintage gear, I’m sure they don’t recap and retube every old amp that comes in, but would if it had the symptoms or if the parts were visibly in need of replacing. |
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Doog
mid-century modem
Joined: 24 Apr 2006
Posts: 21162
Location: London
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| Posted: Wed Jan 29, 2020 12:17 pm Post subject: |
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imma pop a cap in yo amp
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sunshiner
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Joined: 02 Nov 2012
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Location: Around the corner
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| Posted: Wed Jan 29, 2020 3:09 pm Post subject: |
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| Nick wrote: |
| sunshiner wrote: |
| Electrolytes dry up with the time and usually explode. Sometimes, but not often, they catch on fire, considering that amp is built from wood, yes it is advisable to replace them. |
have you ever seen or heard of an amp catching fire due to old caps?
You can usually hear a bad cap in an audio circuit, or see the vents swelling or electrolytes leaking on the board. Several local shops in my town specialize in vintage gear, I’m sure they don’t recap and retube every old amp that comes in, but would if it had the symptoms or if the parts were visibly in need of replacing. |
I haven't heard in amps. I serviced some old industrial circuit boards for a period of time (while being way underqualified for the job) and saw electrolytes that burnt really badly, but didn't cause any fire because the circuit board enclosures were made of metal and textolite. Theoretically it can happen in an old amp considering that some capacitors work under high voltage, but yeah, you'll probably notice that something is wrong with an amp long before it comes to that
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NickS
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Joined: 14 Jan 2008
Posts: 10406
Location: Nr. Basinggrad, UK
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| Posted: Wed Jan 29, 2020 6:13 pm Post subject: |
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I do have some kit that has never been re-capped and some kit that has. If the shop has returned the amp to you without saying they felt it needed re-capping, I wouldn't worry.
Electrolytics that haven't been used for a very long time need to be re-polarised or "re-formed"; in-circuit, this is best done by applying voltage for only a short period to start with. If not well sealed electrolytics can dry out causing a reduction in effective capacitance and a rise in effective series resistance (ESR); this usually shows in mains frequency hum if the smoothing caps are affected and reduced gain if decoupling caps are affected. The high current experienced by smoothing caps with high ESR can cause them to overheat and start venting electrolyte or if they are very old caps with no designed-in pressure relief, explode. |
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westtexasred
Shortscale Cultural Minister
Joined: 26 Apr 2006
Posts: 16610
Location: Minneapolis
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| Posted: Wed Feb 12, 2020 10:30 pm Post subject: |
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Thanks! It sounds fine. Can't wait to hear what my Les Paul sounds like through this.
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Nick
Y'SEE!?
Joined: 20 Apr 2006
Posts: 8603
Location: Albany, NY
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| Posted: Wed Feb 12, 2020 10:55 pm Post subject: |
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| On that amp, does the reverb knob double as the tremolo intensity control? Or is that just the "REVERB INTENSITY" knob? |
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westtexasred
Shortscale Cultural Minister
Joined: 26 Apr 2006
Posts: 16610
Location: Minneapolis
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| Posted: Wed Feb 12, 2020 11:00 pm Post subject: |
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| Nick wrote: |
| On that amp, does the reverb knob double as the tremolo intensity control? Or is that just the "REVERB INTENSITY" knob? |
Just Reverb intensity. You can just control the Tremolo speed,not intensity. maybe you could with a foot pedal? |
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Nick
Y'SEE!?
Joined: 20 Apr 2006
Posts: 8603
Location: Albany, NY
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| Posted: Wed Feb 12, 2020 11:39 pm Post subject: |
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| westtexasred wrote: |
| Nick wrote: |
| On that amp, does the reverb knob double as the tremolo intensity control? Or is that just the "REVERB INTENSITY" knob? |
Just Reverb intensity. You can just control the Tremolo speed,not intensity. |
I figured that was probably the case, I'm just used to seeing intensity as a tremolo control instead of reverb. It's kind of funny, almost like they looked at an amp with two tremolo controls and felt they just had to use all of the words on the control face. |
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