• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

DIY repair- replacing capacitors

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First of all- this should be a sticky subject. Now, though...

I used live in Nevada, where I knew an engineer who had a lot of spare time to work on my stereo equipment for me. Now I live in California, where I don't know any engineers; and I would like to do some work on my amp.

The guy that I knew told me that if I really wanted some wholesale changes to my amp (HH Scott 222-D [fully integrated]) that I should replace all the caps in it. I was having some trouble with the phono stage in it; so all the phono stage caps have been replaced.

Here's the thing- I know what a capacitor is. I know how it works. I know what a farad is. What I don't know is why there are hundreds of different designs for storing that little bit of electricity!!

Should I replace electrolytic with electrolytic, or should replace electrolytic with polypropolyne? What should I replace my old wax-foil caps with? Etcetra...


Capacitors get people all funny :) This is just my 2c:

First things: use only the same voltage ratings (or higher) and I would recommend sticking to the same uF values too. You should definitely replace all capacitors connected to the output tubes and bias circuit, if they fail your amp will melt.

The power supply can-style caps might be ok: if they arent leaking goo and they don't get warm, and there is no hum, they are probably ok to leave.

With regards to film caps: polyproplyene/polystyrene etc only go up to a few uF, and are best used for values under ~1uF. You can get them in values like 47uF but they are massive and expensive. Decent film caps are the likes of sprague orange drops, all the way up to boutique silver in oil ones. Up to you how much you want to spend, I find the orange drops pretty good.

For the smaller lower voltage electrolytics, replace them with modern ones. I recommend the nichicon muse from angela.com, they are cheap and sound good.

I have recapped a few amps and radios, the easiest way is to clip out the old cap leaving the leads, make the ends into hooks then solder the new cap in place. give them a wriggle to check that they are securely connected. Do one at a time, you cant go wrong!

But yeah, good luck :)
The HH Scott site is very helpful; I've been there before.

I took down a list of all the caps, and I have a multimeter to test capacitance. I guess all I really wanted to know is whether or not it's ok to replace one type of cap with another kind as long as the voltage and capacitance values are the same.

E.G., could I just use all orange-drop caps for replacement?
The problem is if you try to replace an electrolytic with a film cap of the same value, the film cap is likely to be the size of a beer can. This can upset the parts arrangement on your circuit board.

Depending on the application, you may find limited options. A 39pf disc ceramic used for stability will be hard to find in a film cap. And not in an elytic either. I doubt there will be an audible difference between the ceramic and a mica in a 22pf cap.

Cap type consideration in the radio section may be completely different than those in the audioi section.

Replace paper caps with film of some sort.

In general they selected types for sound reasons - pun intended - and it is probably best to stick with them unless there are compeling reasons not to.
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