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Post subject: Ramp-Up
Posted: Mon Sep 23, 2013 8:29 pm
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A tech inquiry, my Bassman has been sitting in a studio for a good four months, unused. It's time to get it back home and on the bench for some tweaking. So, I'm wondering what kind of schedule you guys like to reform the electrolytics. I used to take 12 hrs, then 8, then 6, lately I've gone with 2hrs @ 10 volt intervals. Also, have any of you tried the trickle-current method? Thanks, Art

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Post subject: Re: Ramp-Up
Posted: Mon Sep 23, 2013 10:17 pm
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Art, for an amp that's been sitting unused a year or less, you can ramp-up the thing in an hour, no sweat. I start at 60VAC for a 15 minutes -> 80VAC -> 100VAC, then full voltage.

For units that have been sitting around for years (5 years) ramp-up over 3-4 hours. Greater than 5 years --- check the condition of the caps, first. If no leakage or "pimples" --- go for 6 hour ramp-up.


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Post subject: Re: Ramp-Up
Posted: Mon Sep 23, 2013 10:59 pm
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Thanks Steve!!! I tend to go overboard with these guys. On another question: have you ever tried the 10% lower parallel cap approach, as suggested by Merlin? Actually acquired the appropriate caps a while ago, for that purpose. Thinkin' about trying that scenario out, on the Bassman. What do you think? I mean the worst that can happen is they won't fit under the cover, right? And I think the rule of thumb is..."keep the smoke in". Art

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Post subject: Re: Ramp-Up
Posted: Tue Sep 24, 2013 3:54 am
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Art,

You talking about 10% ripple calculation? For push-pull amps this is more than adequate PROVIDED the output tubes are matched to within 10%. As the pair should cancel out the AC hum riding above the signal. Single-ended amps will require tighter tolerance.

With tube rectifiers in guitar amps you prolly want some ripple. As this adds slight delay (or part of the breathing effect) to the amp's tone. Too stiff PS with no ripple leads to a sterile solid-state tone.


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Post subject: Re: Ramp-Up
Posted: Tue Sep 24, 2013 7:12 am
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Please excuse my ignorance, but are you saying that if my amp has been sitting idle for several months, I can't just plug her in and warm her up? Do I need some kind of variable voltage power supply to reset the caps first? Related.....should I be running my amps a min of once a month or so to avoid this?

Thx.
Chris.


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Post subject: Re: Ramp-Up
Posted: Tue Sep 24, 2013 5:35 pm
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Runnerman, usually you don't need to worry about ramping-up an amp, unless it's been sitting for years. Unused electrolytic caps lose their "form" when sitting too long. And their filtering and power handling capacity can greatly diminish.

Best thing to do is use the amp, at least once every few months. Esp those loaded with precious tubes and transformers. Like a couple of hours of use, every six months. It'll keep the lytics happy.


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Post subject: Re: Ramp-Up
Posted: Tue Sep 24, 2013 5:54 pm
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Chris, if it's only been a couple of months, not a problem. Mine's been sittin' for well over four months, and I'm over-protective. I know folks that have fired up amps that have been unused for years, with out incidence. Also, the newer electrolytics are self healing! But yeah, playing the amp once a month for 30min at medium volume keeps 'em happy and healthy. JMO, Art.....oopps-slow post !!!

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Post subject: Re: Ramp-Up
Posted: Tue Sep 24, 2013 7:15 pm
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Art,

Meanwhile back at the ranch.... :lol:

Were you talking about building a PS using the 10% ripple calculations? This is a good parameter. As you want to have that refilling cycle effect. Single-ended amps need 5% ripple due to the lack of phase cancelling effect of push-pull. The use of rectifiers with lots of forward DC drop overwhelms the ripple effect.


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Post subject: Re: Ramp-Up
Posted: Tue Sep 24, 2013 10:28 pm
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No Bro, just thinkin' about some extra smoothing in the pre amp stages of the Bassman. This guy is pretty much of a test pad for my rocket science projects. This is 165, that I totally rebuilt to 864 specs. Rewired, added an adjustable bias, ditched the cheesy tone and coupling caps for Alessandros... the usual hypo upgrades. The poor guy is on the slow cooker, as I type. This guy is a 2X10 combo. Art

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