#1
So recently I decided to mod my Crate V18 212, as is I cannot afford a new amp right now and to sell it I wouldnt get much. So I found a few mods and decided to go with a Trainwreck Rocket mod

Trainwreck Rocket Overlay

I am familiar with electronics but as I was searching for the capacitors I encountered DC and AC caps. How do I know which one to use? The caps that are in the board have nothing other than the ratings. Also is it a big deal to use a lower or higher farad cap than the one listed, would it effect anything other than tone?
#2
To know which ones to use you will need to either understand what the cap is doing in the circuit, or find a better parts list/guide. I imagine there's a better list somewhere for a Rocket, you could reasonably extrapolate from that for most parts.

There's really not such a thing as an AC or DC capacitor. Non-polarized capacitors work in both directions so they're more commonly used with AC, but there's nothing inherently "AC" or "DC" about a capacitor.

The round caps with shading are polarized electrolytic caps. The rectangular ones are non-polarized, usually poly caps like Orange Drops. You usually don't have to worry too much about voltage handling with the poly caps, they're typically rated for a few hundred volts more than that part of the circuit sees.

Using a different cap than the one specified depends on how far off spec you are and where in the circuit the cap is. It's almost always ok to mess around with the values somewhat, and usually only affects tone, although the Trainwreck amps were famous for being fairly sensitive about parts, and might become noisy or unstable if you go too far off.
#3
How familiar with electronics and circuits are you?
I find these conversions more trouble then they are worth. If something goes wrong are you going to be able to trouble shoot it?
Prs se Holcomb is the answer
#4
ahh ok, the reason I ask about the AC or DC capacitors was that when I was looking for components some would only give DC voltage and most were AC. Then I read that apparently you cant use DC rated caps in a AC circuit, I never heard of that before so I came here to ask.

And as for the cap differences were talking about using a 47pF cap in a 50pF spot. At most it would be like 2uF or 3uF difference.

Yeah I should be able to troubleshoot it, ive done a few amp repairs but nothing to the extent of this.
#5
As already noted, most caps can be used in AC or DC situations, usually he non polarized are used with AC but that's not carved in stone. DC applications often use polarized.

Voltage - the voltage marked on a capacitor is the maximum it can handle, not a requirement. If you have a cap in a situation that carries 24V for example, you can use a 100V cap with no trouble, but do not use a 16 V one.

Capacitance - That's the microfarad rating. Usually has to be as close as possible, within 10% usually is fine. Most of the caps used in many guitar amps were 10% tolerance, and many were 20%. In some cases you can change that, especially if you need to adjust the tone. Like my Super Reverb, when I got it, the amp was a standard 70's silverface amp, bass was way too loud and boomy. One capacitor swap and that tamed it a lot, now it's working great.

And so you'll know, electrolytic capacitors, the ones that look like little oil drums, can dry out after 20 years or so. If one fails in the right location it can fry a transformer. So I swapped the electrolytic caps in both of my Fenders a long time ago. I'd rather spend $50 in preventative maintenance than $125 in repairs...And it's a lot less expensive than that if you just replace the electrolytics, I replaced all of them just to get better quality parts in there than the cheap stuff Fender used at the factory.

Most of the Orange drops, metal film, and ceramics will handle any voltage you're likely find in an amp. Orange drops, for example are usually 600V. Not many tube amps have more than 450 to 500V floating around. The ones you have to watch are the electrolytics, many of those will be in the 25 to 50V range, when you replace those get one that is equal or higher voltage handling capacity.

Here's a site with good info and pictures of the different types.

http://www.learningaboutelectronics.com/Articles/Types-of-capacitors
Hmmm...I wonder what this button does...
#6
Thanks Paleo Pete! very informative.

In regards to the AC or DC voltage ratings, on the Mouser site they show on most of the caps they would show AC voltage and DC voltage

Example

See how it shoes two different ratings. Does the voltage rating matter? I ask due to there is a cap I need but the rating that only shows the DC voltage no AC, the DC I believe was 1kV and the cap I need is calling for 400v. Would that be ok?
#7
You can get everything you need from www.aes.com or triode electronics. No reason to go to mouser for just a few guitar amplifier caps.

You'll want 630vdc for your replacement caps.
Prs se Holcomb is the answer
#8
thanks for the sites AcousticMirror! Ill check em out tomorrow when I got some more time. I just hope they dont kill me on shipping to Canada
#9
another question, if I cant find the right size cap, can I put two together to make it the correct size? I was reading about it and people said you had to put some sort of bleed resistor with the two caps. Is it alright to due this or is one one of those things where yes you can do it but you dont get great results
#10
It doesn't look like you are replacing any of the power supply caps. I think the tube amp diy sites will have all the values you are looking for. All of them are pretty standard.
Prs se Holcomb is the answer
#11
Quote by Roc8995


There's really not such a thing as an AC or DC cap.


AC/DC cap:



#12
Lol
I'm an idiot and I accidentally clicked the "Remove all subscriptions" button. If it seems like I'm ignoring you, I'm not, I'm just no longer subscribed to the thread. If you quote me or do the @user thing at me, hopefully it'll notify me through my notifications and I'll get back to you.
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