Misterious Cap, noise issue on NOVANEX AUTOMATIC 6 amp

[razabri]

Hey guys, haven't been able to find the answer elsewhere, so I thought to give it a hit over here...
The cap in question is my main suspect in debugging the device, but I can't measure the capacitance and only thing there is is the wirting - 1500/M 530 FAP
Anyone knows what's it's value?
Thanks!

[DIY Bass]

Photos are probably going to help.  Also, where it is in what type of circuit could help as well.

[razabri]

Alright, thanks for the reply. Here's the pic - it's the first one that meets the input at the plug of an old solid state amp. The thing is, I don't know much about this things, but I try to do as much as I can - the amp works fine, but there's a quiet but evident deteriorating noise at low volume and with the guitar on high, and when you lower the guitar pickup volume and increase the amp volume it doesnt make such noise. I already replaced the big caps on the power stage, as I read somewhere that it might be an issue, but it didn't help. So I thought it might be something about the input, and this cap looks different from all of the others wich are old school fish colored ones.

[italianguy63]

Looks like 330 to me... Probably 33pF 1500V

MC

[razabri]

Thanks, well you got me looking at the picture up close, and now to me it looks like 630... You could be right about the value, but voltage is way too high for the amp, but who knows. The number 1500 could indicate 1n5 maybe... The 630 could be something like 63pF, as the zero vould indicate the decimal thing, like 632 would be 6300pF, but it seems too small of a value - I'm clueless

[italianguy63]

Being that it is pretty good sized... that would indicate to me the small value (pF), and high voltage.

MC

Edit:  I see 600V orange drop caps in guitars all the time... The voltage rating only matters if it is too low!

[italianguy63]

You can always unsolder one side and test it. 

[razabri]

Could be, can't really imagine 1500v going thorugh this guy 
My multimeter has no cap value check option, so I had to go with the writing, hope someone figures it out, or let me know if it matters at all for that small noise issue I'm having...

[Rob Strand]

I have to disagree.   I read it as 1500pF M = 20% and 630V  (hard to read).

The arrangement of the text  value / tolerance was common so too was placing the voltage underneath.


Checkout,
https://picclick.co.uk/NOS-MULLARD-MUSTARD-Capacitor-2200pF-630v-x-10-113916173187.html

[razabri]

Hey Rob, thanks for your input. I guessed so when I said it looks to be 1n5, but it still seems like a really small value of what I'm used to with building effects and such. Still, I'm not sure about if replacing it would do anything better with that noise issue - distorting a bit with guitar on full volume and amp on 1 and not so if you roll back the guitar and roll up the amp - what are your thoughts?

[razabri]

Here's the full picture - I've already replaced two big caps on the right, so those are new, as I've read that these power stage caps can get old and need replacement, as they can make some noise issues.

[anotherjim]

I would have gone with 1500pF but like Paul, I read the lower number as 330 too which I suppose could be the V rating.

Nicely made board. Looks like they split a stock TO-3 heatsink which is a bit of genius.

[antonis]

What about that tropical fish in front of the cap in question..??

[Rob Strand]

Hey Rob, thanks for your input. I guessed so when I said it looks to be 1n5, but it still seems like a really small value of what I'm used to with building effects and such. Still, I'm not sure about if replacing it would do anything better with that noise issue - distorting a bit with guitar on full volume and amp on 1 and not so if you roll back the guitar and roll up the amp - what are your thoughts?

You would need to trace out the circuit to make a good decision.  It could be a design issue more than a part issue.

Here's a scenario which fits what you see (total guess on my part):
- The first stage is relatively high gain.   The amp volume control appears after the high-gain stage.
   The first stage clips and produces the distortion regardless of the amp volume.
   That's why you have to back-off the guitar.

- The amp volume has a treble bleed cap across the clockwise and wiper terminals.
  Since you need to back off the amp volume so much that causes the most treble boost
  and makes it noisy.

The noise could be related to the design of layout of the first stage of the amp.

I would have gone with 1500pF but like Paul, I read the lower number as 330 too which I suppose could be the V rating.

Nicely made board. Looks like they split a stock TO-3 heatsink which is a bit of genius

Open the image in a new Tab so you are viewing it on the image site.  Them click on the image to expand it to quite a large image.  If that doesn't work you browser click the 'Download Original" buttom.   When you look at the full res pic you can see it's 630.

And yes, I also noticed the heatsink.   Not so great for thermal stability of the amp but a cool idea just the same.

[razabri]

Hey guys, thanks for your replies - then the best assumption for it would be at 1500pF. But still, would this cap matter with the slight noise issue at bigger input of the guitar? As I already replaced 470uF caps on the right, those are not the problem, so I thought to approach from a different angle and go from the input - so, it's the first cap connected to the input from the guitar jack. I don't know if it's malfunction would cause any problems, and my second guess would be with other electrolytics in there...

Yes, it's nice little amp, Novanex Automatic 6 and it sounds pretty big for it's low wattage and small speaker. At greater volumes it has it's own sort of compression preventing the speaker to distort, so you can use it for bass practice as well. Circuit looks nice and clean and I went with replacing those caps close to original, axial ones - it felt right to do so. It was a good deal too, for about 20$ I got it off the web, broken, but only the fuse was burnt, noting else.

Tropical fish one seems close, but it's further in the circuit and the one I suspect is right on the input - se the other side of the board.

[DIY Bass]

One thing that I have found to help at times is to follow through the audio path with an audio probe.  If you hear no noise on one side of a component, and noise on the other side then replace the component.  I guess it is not a guaranteed technique, because there are all sorts of reasons you can get noise, but it is a starting point.

[duck_arse]

Hey guys, thanks for your replies - then the best assumption for it would be at 1500pF.

no no no - no assumption. as said by some, it IS 1500pf/ M tolerance/ 630V Mullard or Philips-alike radial mustard cap. very much like the tropical fish, but without the colours. 'FAP' might be a designator, I couldn't find it mentioned. it's highly unlikely to have failed.

it so happens I have one of the exact part shown, sitting in my drawers now this last 35 or more years.

[iainpunk]

What about that tropical fish in front of the cap in question..??

looks to me like blue gray orange
68nF
i could be wrong tho

cheers

[danfrank]

Who wins the jellybean count in a jar prize?!?
Lol
Its 1500pf, 630 volt. Those old Mullard radial caps have leads that easily separate from the body of the cap. Any amount of side pressure will do this. Then moisture creeps in which is a possibility for noise. They are great sounding caps but very fragile.

[italianguy63]

I apologize for being wrong!  It happens.  MC