Rocket Documents Discussion

[TimDude]

Hopefully it's not taboo to comment on an old thread. I have a question regarding the bill of materials vs the schematic. I'm planning on building one of these Rockets and I was putting together an order online. I noticed on the schematic calls for capacitor-5 (C5) to be 50pF. The bill of material says 47pF 630V is fine. But the part that the bill of material links to on Digikey's website is 47uF 630V. Now I'm still a novice, so maybe I'm missing something. 47pF is vastly different from 47uF, right? I'm also looking at Ceriatone's schematic and they also call for a 47pF capacitor for C5. Lastly, do I legit need a 630V capacitor? There's pretty much only one of those for sale on all of the Internet and it's at Mouser.
Here is the link to that part: https://www.mouser.com/ProductDetail/Mu ... v%252B4%3D
Or will a simple silver mica 500V capacitor work like this one here: https://www.amplifiedparts.com/products ... ver-mica-5
Or will one of these big buck $$$ silver mica 500V capacitors here work: https://www.mouser.com/ProductDetail/Co ... %252BUs%3D

Thanks for your help and thanks for putting this forum together. You folks have a lot of good info here.

[pompeiisneaks]

I've moved this comment to it's own thread, so as to keep discussion in the discussion section, away from the files themselves.

See: https://ampgarage.com/forum/viewtopic.p ... 684#p54661 for the files thread this question refers to.

The difference between 47 and 50pF is within tolerances of the capacitors themselves at this use and level, and won't make any difference. 500V should be fine, as the tubes on either side are operating in the 300ish voltage range in most cases, and in this one it's off the cathode of V2 over to the grid of V3 (PI) so it shouldn't even be in a very high voltage situation. If a tube fails, though, it could be near the anode voltages of the tube, in theory, if a dead short happens.

You can use silver mica or ceramic X5F type (for audio use) in this location, but I'm not sure what's more 'appropriate' for the rocket. I'd suggest seeing if someone else that's more knowledgeable here could confirm what the originals used. I've had bad luck with small pF silver mica caps being pretty microphonic.

~Phil

[pdf64]

Which version bom are you referring to?
If a link that’s supposed to lead to a 47pF cap instead goes to a 47uF cap, then something is amiss.

[ChopSauce]

Err... if the bill of material does mention a 47uF cap for the tone stack, that could be a mistake worth mentionning in the files section...

For what it's worth: gutshots of two express (from the files/ section) show what looks like a silver mica cap as C5. What do the other cloners use: couldn't you see pictures of their builds?

[pompeiisneaks]

The BOM says 47pF. The link is to allied electronics. I am guessing something may be amiss with the digikey website, or you've accidentally confused part numbers between two things? I'm pretty sure these BOM's and files have been used hundreds of times, w/o people noticing an error like that would be odd at best.

~Phil

[TimDude]

You can use silver mica or ceramic X5F type (for audio use) in this location, but I'm not sure what's more 'appropriate' for the rocket. I'd suggest seeing if someone else that's more knowledgeable here could confirm what the originals used. I've had bad luck with small pF silver mica caps being pretty microphonic.

~Phil

Thanks, Phil! I looked up photos. Everyone uses a Silver Mica cap there. You don't sound too keen on Silver Micas, maybe I'll give the "ceramic" a try. This will be my fourth amp build, but the first one where I'm sourcing all of my parts. It's pretty exciting. I'm learning a lot.

[pompeiisneaks]

Now I've not built a rocket, I've built a liverpool, and more fendery types have been my past builds. I've used some silver micas and some ceramics. Tone wise I've always preferred ceramics... This is a personal preference, they don't cost a ton, you could buy some of each and try them both out... up to you.

~Phil

[TimDude]

If you're still there, Phil, I have one more quick question. It doesn't matter if I go up in voltage rating, correct? For example, one of the capacitors is supposed to be 100pF 500V. I can use a 100pF 1kV, and it shouldn't change anything, or put anything at risk, correct? I know if I were to drop the voltage, that can put me in trouble.
The silver micas I was originally looking at are here: https://www.mouser.com/ProductDetail/Co ... XDEtvTA%3D
And the ceramic disc I'm now considering are here: https://www.mouser.com/ProductDetail/Vi ... 252BnVE%3D

[pompeiisneaks]

You're absolutely right. You can always go higher but never below safe voltage ratings. as voltage rating goes up, cost goes up, but in this case it's not really a big deal. Especially since the ceramic is 1/3 the cost of the silver mica. Both brands are top brands for this kind of thing, The C0G(NP0) are definitely the right ones for audio path, I swear I also read X5F work well too but now I'm not finding data on that. Either way give it a go.

~Phil

[M Fowler]

It just depends how nerdy you are on components. Some want to copy the Trainwreck amp like an original which can be damn hard unless you have old stock components to work from.

Take for example some don't want to run 25uf/25v bypass caps they want 22uf/25v.

The dropping string resistors 9k1 sometimes are hard to find, why not 10k instead.

Mark

[dorrisant]

Don't stress over ceramic or mica. Either will work, change it later if you're curious.