Capacitor jungle

[gct]

Hi
Just trying to find better in and out capacitors for my TBone SCT800 (Apex 460)

The input cap is 1000pF 630V axial and out 1uF 400V electrolytic radial at the moment.

I read polystyrene for the in and polypropylene out. The results are mind boggling for the newbie ranging from 0 to 30€ and too big or non existent.

Can someone shed some light on the possible specific capacitors/voltage/type/manufacturer/supplier before I go crazy and where I can get them in europe. (Or international shipping)

Cheers

GCT

 

[gct]

Sorry maybe I've misunderstood. There is a 1000pF between the capsule and the grid. I thought this was the input. And a 1uF between the plate and the transformer. I thought this was the output.

 

[gemini86]

well first off, the 1uF doesn't really NEED to be 400v... maybe more like 300 at most. (I'm assuming a 200 something b+? - too lazy to search around for that info)
second, what are your space requirements? I like the mallory 150 style axials, but you would also do well with a wima radial.
third, just grab the first 1000pF polystyrene you find at farnell... vishays are good, you you want to narrow your search down.

Hope any of that helps...

 

[PRR]

> maybe I've misunderstood.

No. _I_ misunderstood, and withdrew my comment while you were posting. I didn't realize that this is a capacitor microphone.

The 1000pFd input cap is probably inoffensive. If you must: 1,00pFd NP0 Ceramic is good stuff. A 500V Silver Mica is never a bad choice. 680pFd will work about the same; they only used 1,000pFd because it is more commonly in-stock at factories.

The output cap.... 1uFd 300+V poly is probably cleaner, BUT you have a real space problem stuffing a huge film cap inside a microphone. Which is the other reason they used an electrolyic. (The #1 reason is the cost of a large film would eat all the profit in a low-price mike.)

Last time I used 1.0uFd poly-film it was by far the largest part in the box. Whiich was bigger than a microphone.

You could go 200V metalized poly, but there is a risk that when it arcs-over it won't clear in the metalized cap but "clear" (i.e. ruin) the transformer.

 

[gct]

Thanks. It's gettiing clearer.

Cheers

GCT

 

[gyraf]

for an input capacitor in a circuit like this, you'll probably want something that is extremely tolerant to environment humidity while keeping insulation properties, and for that, polystyrene is very good. And nearly always used as frontend cap in good mics.

Jakob E.