What caps should be replaced & with what type?

[Perkinsman]

I'm new to audio repair and want to learn to repair vintage tube equipment. I've read alot here and on other sites about immediately replacing caps with quality caps but I'm not sure which ones to replace and which ones to leave. Most sites say replace all electrolytics, but does that include non polarized too?...are the little ceramic disc type caps supposed to be replaced? Also, is it advisable to replace the old cylindrical caps with new smaller mylar or poly ones or should I stay with the cylindrical shapes?

 

[elektronror]

All electrolytics (including bipolar) should be replaced after 20+ years. All other sorts, such as film or ceramic are supposed to last a lot longer.
You can upgrade capacitors in places where they effect sound to something better (polypropylene) but it is often costly and they may not always fit.
Shape does not matter as long as they fit.

 

[Perkinsman]

Ok, how do I identify the ones that affect the sound? I've read about power supply caps, filter caps and coupling caps. Is there a general way to distinguish them and determine which affect the sound? Do they all get replaced by poly caps?

 

[elektronror]

This is the hard part. If you have unlimited amount of money and space, every capacitor affects the sound in some way or another but what affects the most are coupling capacitors.
Coupling are the first thing to look at. Get some nice polypropylene and you will definitely hear a difference.
Power supply capacitors doesn't affect the sound very much so it is better to spend the money on the coupling. Get some decent Panasonic FC and it will be enough. You can always try to bypass them with small polypropylene.
Filter capacitors is the same as the power supply capacitors.

 

[Perkinsman]

Good to know. I assume the coupling are polarized. How do I know where the coupling, filter and power caps are physically located in general? Does each have a certain appearance? Are they marked on the schematic? If so, how?

I brought a non polarized (.03 uf 50V)cap to the local electronic store. It was cylindrical and about 2" long. The tech gave me a mylar (metal film) with close to the same values. If I understand what you're saying, then it should be ok to leave my ceramic discs alone, use the mylar one for the non polarized cylinder and look for good polypro's for at least the coupling caps.

 

[elektronror]

Coupling are not polarized.
Filter capacitors are often located near the transformer and they are big. The rest can vary so you need to understand how a schematic works and what everything does.
Have a look at this schematic. C9,C6 is the filter caps. C1 is coupling. C3, C4 and C5 are decoupling. C5 is for the feedback circuit (coupling).
http://diyaudioprojects.com/Schematics/images/Mullard-SE-EL84-Tube-Amp.png

0.03uF 50v? That voltage does not indicate tubes.
Leave the ceramics and replace all electrolytic and all paper wax capacitors.
If you would post a pic of the underside of the amplifier and a name we would be able to help even more.

 

[sony6060]

Already mentioned- replace electrolytic type caps. Sonically, coupling caps have the largest effect. Rebuilding for others? Forget boutique caps. No one will pay the $300 upgrade.

Biggest bang for the dollar are Russian K40Y-9 coupling caps. I buy in larger lots for about $2-3 each including shipping. And, I rebuilt newly rebuilt from others with that other cap. Members right here at AK will tell you night & day difference after the K40Y-9s were installed. (Some say no difference in various coupling caps).

BTW- do not change the value of feedback caps with out using lab equipment.

My 2 cents.............

 

[Perkinsman]

On the schematic I can see that the filter caps are significantly larger value but I don't know how to read all of a schematic yet to distinguish the coupling or decoupling. Also, are filter & power supply caps the same thing? I'm taking electronics classes now and expect to learn eventually but of course I'm anxious to "do" something instead of reading DC theory. So from what your saying, all electrolytics (polarized & non) get replaced, and the coupling are the most important so they should be poly. So I'm assuming the coupling caps must be the ones others refer to when they talk about Solens or Auricaps and you guys like Panasonic & the Russian K40Y-9's. I'm trying to figure out how to post a pic of the Eico hf30 and will as soon as I do.

 

[sony6060]

Power supply and filter capacitors are the same in this case. The caps 'filter' out the AC component in the DC power supply to a large degree.

I would look up coupling capacitors on a Google search or in an electronics educational book. It would be rather wordy here to explain where coupling capacitors would be located without explaining how an audio amplifier performs plus reading schematics. Schematics are cool in that it is like a universal language all read the same no matter what ones primary speaking & reading language. The symbols are slightly different from Europe, Asia & US, but 'read' the same.

Interesting how some or most of us do not even need a schematic to troubleshoot or rebuild an amplifier. I certainly needed guidance early on. After a while us techs memorizes the tube pins on a socket for most tube types and the associated components fall into place without thinking about it.

 

[FidgetMaster]

Power supply/filter Electrolytic's DO impart their own sound between different manufactures/Specification's despite how many people disagree with that constantly, I don't care if its not directly in the signal path or not, Its still hooked up/connected.... I can still hear the difference some not so much depending on design while others I heard some pretty damn BIG jaw dropping difference's/coloration's......

 

[Perkinsman]

Pics of Eico hf30

Here's the pics of the Eico hf30 chassis top and bottom. Correction: In earlier thread, I stated that I purchased a .mylar replacement for a 03uF 50V nonpolar cap, it should have been .03uF 600V, good catch Electronror.

 

[elektronror]

Nice looking amp. Would sure be nice to own two of those.

If you are going to make a full recap here's what you should do.
C7A-D are the filter capacitors. They are essentially two 20uF 450v and two 10uF 350v.
C8 is a Y2 or X2 capacitor. This means it is tested to work on a AC and if you happen to touch it, it won't kill you.
C9, C3, C6 are coupling caps and should be replaced with polypropylene.
C1, C4 can be replaced with whatever suits you but using polypropylene will be the best choice.
C5 and C2 are electrolytic. It would be wise to choose a high temp cap here. Preferably 105°C+.
While you're at it, measuring all of the resistors is not a bad idea.

 

[sony6060]

Power supply/filter Electrolytic's DO impart their own sound between different manufactures/Specification's despite how many people disagree with that constantly, I don't care if its not directly in the signal path or not, Its still hooked up/connected.... I can still hear the difference some not so much depending on design while others I heard some pretty damn BIG jaw dropping difference's/coloration's......

I agree with that as I hear it. The power supply capacitors are in indirectly in the audio path. I prefer CDE electrolytic capacitors. I also like oil and poly type capacitors when room permits.

A tube modulates high voltage DC so why not build a low ripple with low DCR final capacitor. And, a voltage doubler should have a separate capacitor on the output.

 

[Perkinsman]

Correct schematic for my model Eico hf30

Thanks for the continuing help. I just found out that there were multiple versions of the hf30 and my initial schematic was not the model I own. Here is my model. Sorry but I guess I have to start again by asking what each cap is and what I should replace them with.


Edit Note: sorry, the image is blank, I'll follow up with a good pic of my schematic model.

 

[AudioSoul]

I don't mean to pirate this thread. Sorry to the OP. But I have been following this thread with interest. What is meant by bypassing capacitors? When I look at pictures of preamps that have the capacitors bypassed I see the original caps with other caps added to them. So it seems anyway....

 

[elektronror]

I don't mean to pirate this thread. Sorry to the OP. But I have been following this thread with interest. What is meant by bypassing capacitors? When I look at pictures of preamps that have the capacitors bypassed I see the original caps with other caps added to them. So it seems anyway....

Essentially you just put another capacitor in parallel with the existing one. This can have a very good effect but sometimes you can never hear any difference at all.

 

[Perkinsman]

Schematic for Eico hf30 with 7247 driver tubes

Ok, here is the correct schematic. I hope someone could break it down into the type of cap each is, ie, power supply, filter, coupling, etc and the type I need to replace it, ie, poly, metal film, ceramic disc, mylar, etc. btw, does mmf mean pico farad in the old days?

Electronror did a neat job a few threads back but it wasn't the correct schematic, my bad. I owe him a drink.

Also, I ordered 2 can replacements from AES today with the same values and a little higher temps, so that takes care of 4 of the 10 caps. The only other electrolytic is C2.

 

[FidgetMaster]

Yes I like CDE Electrolytic's myself I am very impressed with their 381LX series being they are a cheap/budget pricing and I replaced some old United-chemicon's with equivalent CDE 381s and that was a jaw dropping difference the CDEs added some much needed clarity and neutral behavior all over the frequency spectrum. the chemicon's were still good and within spec but I thought they added a little too much sharpness/presence to the sound kinda same way Nichicon electrolytic's do.

 

[gadget73]

mmf = micro microfarads, or picofarads in modern speak.

any chance you've got a bigger schematic? I can't quite make out the part numbers.

the power supply caps will be the ones connected after the rectifier. Its probably a multi-section can. It may or may not also include the two smaller, low voltage cathode capacitors. All of those need to be electrolytic types.

The others you can use just about anything you like. Any sort of film capacitor is plenty suitable to replace what is probably either a ceramic or a paper capacitor. You can use different types to play with the sound if you like, but a good starting point is a Sprague 716p "orange drop" type. They're not real expensive, and they're just about bulletproof. I also use a lot of inexpensive yellow film caps that you can get at most places that deal in old radio parts. For small value picofarad caps, I usually use a silver mica, but mostly because I've got an assortment of them. Other types are not as easy to find in small values.

 

[Perkinsman]

ohhhh, micro micro farad, 10-6 or pico farad, makes math sense...funny.

If you Google Schematic for Eico hf30, you'll find a pdf with all the specs and it will allow you to blow it up too but for some reason, it's not letting me copy it any bigger.