Replacing Coupling Capacitors in Vintage Gear

BG236 - Why you should replace coupling capacitors in vintage gear and how to best go about it. This applies to old amplifiers, tuners, preamps, tube gear, computers, TVs, stereos, receivers, ham radio gear, etc.
Link to PTFE Tubing I use. Check sellers other auctions, I use a variety of ID from 0.7mm, 0.9mm, 1.0mm, 1.1mm, etc.
www.ebay.com/itm/3-10M-PTFE-T...

[@mojomanxero8632]

Great video! I'm learning amp stuff as a computer engineer and the way you covered the electrical engineering part was perfect. I do understand the math involved for changing a coupling capacitor and your approach to helping us amp noobs understand sound sculpting is really spot on. Thank you !

[@derekec]

Uh...simply Wow!. So many experts teach way above any beginner's level that we (I) end up really understanding nothing and go on that way for years (decades) because other life gets in the way. Finally at 64 I'm understanding, know how/what to do and can advance on to the next. Still so many questions on even knowing how to identify the tube pins, etc for testing with meter but if you are hopefully teaching it, I'm in and know I'll advance more. Immense thanks.

[@jeffreygang]

This is fantastic! Best capacitor explanation I've come across so far.

[@peteleoni9665]

Absolutely incredible video. Every line a gem, one of the cleanest most direct explanations of coupling capacitors in the universe. I am floored. Between you and Uncle Doug, the difficult is made simple. Thank you endlessly.

[@Frustratedfool]

There are certain times in life where something that has eluded you suddenly comes into sharp focus. This is one of those videos that prompts that ‘penny dropping’ feeling. Great video, Mark. Super explanation.

[@preiter20]

Thank you for this video Mark. I hope you are healing well. This level of detail is exactly what I was looking for. In audio equipment I was concerned about not matching 100% the capacitor values but now I understand the implications of a change in value. Knowing how test the impact of changing capacitor values is important to me as well. Thanks again!

[@tinkeringwithelectronics]

Mark I hope you're feeling better, your healing is in our prayers. Great video, thanks for taking the time to make it. Josh

[@kylenovak97]

This is an excellent series on vintage. Keep it up! Part classroom, part hands on, part continuation on the EICO. This is a perfect format.

[@johnfindley1188]

Thanks for a great video! The explanation of coupling capacitor is the first time that I understand how they work in a tube radio circuit. I am a hobbyist restoring tube radios. i have attended some radio restoration courses at our local vintage radio museum here in the Twin Cities. Actually tomorrow there is a special meeting on how to improve the classes. I will bring up your videos as a great way to teach how to work on vintage electronics. Thanks again. John

[@josephmagedanz4070]

Very helpful for us beginners...thanks!

[@gregcharles999]

thanks Mark, very informative and helped me understand well the relationship of the Coupling Caps. I do my best at cap jobs and the such on my old Fender amps and try to learn as i go along, this has helped to explain a lot i didn't quite grasp. thanks again!

[@tanveernaeem1157]

Really enjoy your videos. I love the way you explain things with a touch of theory and real life demonstration. Great learning experience. Please keep up the good work and thanks for sharing your incredible knowledge.

[@banjoperator]

nice video Mark, informative and well done.. i had always gotten this confused as i travel the hobby electronics road.. now this goes into my folder of explanationd.. keep them coming and wishing you a speedy recovery....cheers

[@davidschmoll3681]

Thank you for your articulate explanation and patience!

[@turnersparadise8368]

Thank you, Mark, for all these videos. I have ordered 90% of the BOM for the KT88 build. I am so excited. I have worked up to this point for well over a year now. Also building two Fostex FE206FN DBR speakers using their plans. Now all I need is a good RIAA tube preamp. Hint hint... :-)

[@rodneykroetsch2924]

You have great explanation skills. Very informative videos!

[@richardmawdsley2589]

thankyou that was very useful for when I'm restoring old reel to reel recorders

[@birdb461]

Thanks for a very well organized and useful cap video!!

[@GeorgeEI7KO]

Great video Mark. Thank you. Happy st Patrick's day tomorrow from Ireland 🇮🇪

[@curtisgriffin7924]

Excellent video! You also explained very well the +/- on film caps I have seen on some KZbin vids. Always thought that it was another thing that I could put in the $5k power cord will make your system sound better group. Always have thought if it sounds good to you then it is good. All depends on the individuals hearing, same as the $100 + coupling caps out there.

[@danielsaturnino5715]

This is great content and very explained. Thank you

[@alphanuevo]

Thanks so much for your content. It is quite helpful. I'm restoring an old console pull tube amp so this is great.

[@loricastro3772]

Amazing class! Thanks for show.

[@martymcgill1312]

This is great info and very helpful. Thank you

[@drtidrow]

12:40 Component tolerances for these types of caps are typically 20%, so there's a pretty big overlap in the acceptable range of values between a vintage 0.5uF cap and a modern 0.47uF one. For all practical purposes they're equivalent.

[@gfodale]

Just wanted to say thanks for another very informative video. I'm getting set up to repair old Amateur radio gear, still needing a few items of test equipment. The information here is of great value. Having to refresh things I learned in '79. Also, back then I had a supply system for parts ordering, rather than having to source them on my own. Good information through-out.

[@drtidrow]

I've had good success with Mouser, they'll get even small orders out in a few days, as long as they're in stock. The biggest issue usually is figuring out which of the dozen or so search returns is best for your application. :-)

[@gfodale]

@@drtidrow Agreed, used them for the first time a bit over a month ago. Was quite happy with the experience. Prices reasonable, and shipping was far quicker than the folks I was using prior. They're now head of the pack.

[@sufisafavi5531]

Thank you for sharing! Very educational.🙏🏻🎶✨

[@gearheadted9210]

Great explaination,thanks!

[@bucyruserie1211]

Your the only person I have ever heard call them "decoupling" capacitors.. However, I think it's a much better term for the function of the capacitors as you stated..

[@firecatfly]

I learned alot! Many thanks!

[@anhbaoconnecticut3128]

Thank you for posting!

[@briancampbell7712]

thanks for the video...I have only handled replacing my speaker capacitors...and trying to hear some differences with other manufacture caps...my brain will fry if I get to deep into thinking that hard🤣...

[@SciPunk215]

Good stuff right here !!

[@Dan-vb3ju]

Read below as even though you mention on the Eico HF85, the 6x4 tube in tube manual states" max 10uf". Eico used 20uf for the first stage, but actually I have used 50uf for years and never had a 6x4 fail. It depends on the design. These preamps really require extra filtering to keep hum down to a minimum. I have posted some info from am engineer that did a lot of work on Eico gear. Regarding the first filter cap -- and specifically when vacuum tube rectifiers are used -- the issue relates to the "hot switching" specification for the tube used. That is, the use of an excessively large first filter cap size is not at all about damaging the rectifier tube at routine turn on events. Under those conditions, the filament warm up time -- whether it is of the direct or indirectly heated type -- along with the DC resistance of the power transformer's windings provide virtually all the inrush current protection necessary with regards to protecting the cathode or filament of the rectifier tube. With hot switching concerns however, that relates to conditions where the the power is removed and then rather quickly reapplied (or "switched") with the cathode (or filament) still hot -- ergo the term. Under those conditions (we've all had rapid power line cycling events happen, haven't we?) the peak current impressed across the tube can be very large if the filter cap has significantly discharged itself during the down time, and the AC waveform is then reapplied at the peak of its crest. If the cathode is still hot under those conditions, it can be damaged instantly. Often, it is in fact during power line cycling events when many rectifier tubes fail because of this reason. Therefore, the tube manufacturer's recommendation for the size of the filter cap directly connected to the rectifier tube should be heeded. Further on down stream however, the comments given for those caps above apply. Relating all of this to the HF-85 then, because of the significant resistance placed between the rectifier tube and first filter cap in this design, there is virtually no concern in raising the value of the first filter cap regarding hot switching issues. In this case, increasing it to 50 uF is just fine. The remaining caps then could easily be tripled in value or more for improved performance. In any event, it would still be a good idea to break the 10K B+ dropping resistor into two 4.7K sections as mentioned above. Using only a CRC (two stage) filter before the first audio tube supply point is marginal design for any vacuum tube preamplifier -- regardless of the size of caps installed. A three stage filter is best before powering the audio tubes, and it will be seen that Eico wisely corrected this design error in their followup preamp offering, the ST-84. I hope this gives you a better understanding of the basic concerns regarding the HF-85's power supply design, and how you can best address them for improved performance.

[@youtubeaccount931]

this was good, i learned alot thanks

[@curtisprice9806]

THANK YOU VERY MUCH FOR THIS INFORMATION!!

[@pybelleau]

Very usefull info. Nice

[@scottohta2192]

You do a great job explaining the ins and outs of electronics, can you tell me where you buy your parts from, ie capacitors and resistors, you seem to have them in bulk. Great job! Thanks!

[@qkitselectronics5415]

23:30 good solder! :-) excellent video.

[@hubbsllc]

It was my understanding that when replacing caps the idea was to connect the outer foil terminal to the side in the circuit that has the lowest-impedance path to ground. This helps the outer foil of the cap to act a bit like a ground shield for EM/RF interference.

[@simonlinser8286]

oh so how do we tell which leg goes to the outer foil? and my understanding was that it depends on which direction that DC component is coming from... totally abstract concepts in my mind, i just try to follow the schematic, kinda like paint by numbers, because I'm still learning. but i think your point will stick with me, because it makes sense, i just need to file that away for later. and you do mean this in terms of an electrolytic polarized cap right?

[@hubbsllc]

@@simonlinser8286 No - not electrolytics. One method is to hook a cap up to an oscilloscope set to very high sensitivity on the vertical amplifier, then touch the outside of the cap with your finger. Then switch the scope leads to the cap and do it again. Of the two ways, the one which gives you the least induced noise is the one whose lead is connected to the outermost layer of foil and that's the lead that should go in with the least impedance to ground.

[@dparham]

This is a great video

[@MrAudiophile101]

Thank you teacher

[@mikesradiorepair]

The outer foil is actually very important. Install the capacitors in the wrong orientation and it can induce a large amount of noise into a circuit. I have had radios sent to me that customers recapped themselves and their complaint was that they had a lot of noise in their receiver. Disconnect the non polarized caps and test them and I usually find about 1/2 of them are backwards. Do nothing more than turn those capacitors around and the receiver magically becomes dead silent. The outer foil of a capacitor acts like a antenna and can pick up all kinds of unwanted noise. It's very easy to sort your capacitors and mark the outer foil. Just attach the cap to a oscilloscope and grab the body of the cap and then reverse the leads. The side attached to the scope plug that shows the most 60Hz ripple voltage on the oscilloscope is the outer foil side. Mr Carlsons Lab here on KZbin has done some very good videos on this topic. He also shows how to make a tool for sorting and marking the outer foil of caps.

[@countryside8122]

How do you test them for polarity?

[@bobroth1951]

I agree with you Mike, The outside foil is very important, especially in tube amplifiers. The outside foil side should go to the side with the least impedance. Any extra noise will be amplified by each stage. Mr Carlson's lab has a great video explaining this. If you install all the capacitor's backwards-your amp will not sound as good as it should.

[@johntempleton6368]

Well I feel pretty stupid having just bought 2 types of Mundorf coupling caps that cost $40+ each. Those are almost considered "budget" caps compared to some of the audiophile products available. I'm going to dig into that formula a bit and see what I can learn. Great vid. Mark.

[@andywander]

Thanks for the videos! Why the tilted tube in that amp?

[@nickk6109]

If you want to alter the design, what you can do is trace out the schematic then use ltspice to create a bode plot for proposed change. It will also teach you you need to understand the ESR and miller capacitance for example. It won't be perfect but teaches you a lot.

[@stuarthossack7906]

Hi, if the power tube were to receive a high CD offset, presumably it would be biased "hard on" ....... what's the likelihood of burning out the output transformer as well as the power tube?

[@taineasy]

Hi there. I am rebuilding my Heathkit ar1500a ss receiver amp and an wondering if I should not replace the tantalum coupling caps with something else? The original caps are 10 uf 15v polarized tantalum. What would be a solid replacement. Have had a few builder friends suggest I go with 22 uf. Should I consider this and maybe bump the voltage capacity value as well. Most of the caps are in a amp output and phono preamp section. I do have a couple 10 uf's on the tone control section and one 47 uf on the main power amp supply. Your opinion would be greatly appreciated. I have replaced the old 5w resistors (sandy's) with 10 watt mills which I think would be better as they do get warm. Thanks Mike

[@gri7]

I have a harmony amp from 1961. Replacing a few parts. It's all original point to point. Dunno how much to replace

[@stuboyer1901]

Good one Mark. You have a problem with your mic isolation. As you talk you're thumping something, either by hand of with your foot, and it's amplifying through you mic.

[@MrsG7swr]

Thank you for this as a much a refresher as it was new information. I see the inner foil debate rages below, One thing people often forget is the tolerance. for example I have had the odd customer here or there wanting to reject a resistor as it was not 1K ohm but was within the marked/published tolerance, I did explain nicely! I would consider that replacing a 0.5uf at 20% with a 0.47 at ten or better gives a difference not worthy of concern and could even give a capacitance closer to design than the old parts if as new they were at the far end of the tolerance to start with. I am trying to find out if tesla are still making poly caps for interstage decoupling as i local veteran repair shop was waving some at me but my skills in Czech were only matched by his in english so almost no understanding. i recall the old Philips/BC (now vishay) electrolytics were plus 20 minus 80 percent.

[@dannyjanssens7787]

can you replace old capacitors on a vintage linear turntable with tantalium capacitors?

[@jameshenz1780]

Very informative videos and I thank you! May I ask you a question ? I'm trying to get and keep my guitar amp running at its peak performance. While measuring orange drops , there is moderate levels of DC present on one side. The other side measures a few millivolts. Would you consider that a leaky cap? And one more if I may sir, on one or two orange drops, there is decent levels of DC on both sides. Is that just dependent on the circuit or , no matter what , there should be no DC voltage present? Hope you understand. Thank you for your time! I'll keep watching. Blessings, Jim

[@drtidrow]

Depends on the circuit design, that could be completely normal depending on the biasing scheme and other circuit considerations.

[@jameshenz1780]

Greetings again!! Question sir if I may. My mid and bass pots have little to no response in my tone stack. I test them like you suggested. I put common probe on chassis for ground reference then take red probe and test at the plate slope resistor at V1 which has high voltage sitting there. Then I take red probe and test where other lead of orange drop connects to pots. They read .2 to .4 millivolts. Would you call that the correct way to test and if so , would you consider them not leaky? AND, even if they aren't leaky, can they still be bad? Thank you for your time!!! Blessings, Jim

[@viol999]

Just a noob question...why did you replace those .25uf caps with .22uf caps instead of .27uf?

[@davidbishop5736]

MikesRadioRepair is correct. Those new replacement caps can be measured to see how noise can become part of your circuit. Try out that measurement Mike talks about for yourself. You might be surprised.

[@6StringPassion.]

I just built a vintage solid state amp from a kit that was made in 1965. All of the caps in the kit except for a few are electrolytic, and I purchased brand new ones rather than using the originals. I did use the original 6 ceramic disc caps and 2 mica caps though. The amp is motorboating. Someone suggested that it was a faulty coupling cap, but how can I tell which caps are the coupling caps? Are these always the non-polarized caps (disk and mica), or could they be electrolytic?

[@drtidrow]

As far as I know, electrolytics don't get used as coupling caps, as they tend to be inherently "leakier" than other types. Usually coupling caps are disc or tubular metal foil types, mica caps generally are reserved for oscillator and tuning circuits where their temperature stability is desirable.

[@dennistowne457]

You said that when these caps age they start to allow dc to pass thru. Other than messing with the bias and stress the tubes does it create hum or other noticeable distortion?

[@drtidrow]

Definitely - the shifted bias level could massively distort a signal passing through, as the tube in question might be driven into "saturation" and clip the signal.

[@russellesimonetta3835]

You can simply test coupling non polarised caps by checking with an instrument/ guitar cord! Plug into a guitar amp clip alligator clips to the hot tip and ground shaft, o.k.? Put the other end of the clips to the leads of the cap. The quieter side is the + side.

[@on1ytheb3st]

Will a leaking coupling cap only degrade the tubes of the next stage, or will they also overload many other components as well? I've gone ahead and replaced many components already on my tube amp (electrolytics, power resistors, filter cap balance resistors, etc), I'm worried if I don't also replace the coupling caps, they'll destroy most of my brand new components rendering my efforts pointless. I can deal with replacing tubes but I'd hate to have to tear my amp down again and redo everything I just did. I do not know if any are leaking but just the thought of the possibility makes me want to just go ahead with it and replace them all? Seems like the effort to test each individual coupling cap would be better used to just desolder and replace (I only have a DMM not an analog multimeter), but then again they are one of the largest contributors to tone right? My amp is almost 35 years old at this point, any recommendations as I'm going in circles with which route I should take.

[@drtidrow]

Well, a 35-year-old amp probably is using the more modern poly film caps, generally the old oil/wax-impregnated paper caps are found in vintage tube gear dating from the early '60s and before. As for whether a leaky coupling cap can overload other components depends on what's connected to the following stage - I'd check any cathode bias resistors or plate load resistors, as excessive tube currents caused by leaky caps might have exceeded the wattage ratings of these resistors. Often this will show as a "scorched" or "burnt" appearance of the resistor in question. Even if they don't show any obvious discoloration, the excessive heat may have caused them to drift in value, so I'd check them and replace any that were outside of the tolerance range.

[@oakmountainman7872]

Hello Mark. I have heard the term "death cap" before but have not seen a video on these. Could you do a short video on these?

[@DaveMcAnulty]

kzbin.info/www/bejne/h2HNfmNrqN2saJo

[@bobmead8184]

Thank you for your videos. I am just learning about tube amplifiers and would like to confirm if I understand the process correctly. You mentioned 400 plate volts on the coupling capacitor(on about 7th minute of the video), but isn't it actually less then 400v because of the voltage drop on the plate resistor? So, it's more like 360-380 volts of something. This is just for my understanding of how AC/DC currents work in an amp. Most probably, you are concentrating on a different topic and just generally call the voltage plate 400 volts? Again, this is not for the sake of argument or making a point, I am just trying to understand how things work.

[@argcargv]

On changing the component values also keep in mind that these old capacitors were only really accurate to about 20% tolerance, so a change of value of about 20% is well tolerated. Choosing the nearest commonly available value will get you within 20%.

[@davidnguyen5028]

I need to change my existing coupling capacitors from .02uf 600vcd to .01uf 800vcd, is this going to drastically change the sound of my push pull EL84 stereo amp?

[@argcargv]

@@davidnguyen5028 That is a change of 50%. Depending on how it is used in the circuit, it will probably increase the low end roll off frequency. That might be a big deal or not depending on how low in frequency you need your amp to go.

[@davidnguyen5028]

@@argcargv so since I’m going with a smaller number, I will get more bass?

[@argcargv]

@@davidnguyen5028 No the opposite, a smaller number will get you less bass. Lets just say that the cutoff was at 50 hz before, with half the capacitance it would be around 100hz.

[@gfodale]

@@davidnguyen5028 If they're not too large, put two of the 0.01uf cap's in parallel for a 0.02uf value, if you're having trouble finding the 0.02uf.

[@davidnguyen5028]

I need to change my existing coupling capacitors from .02uf 600vcd to .01uf 800vcd, is this going to drastically change the sound of my push pull EL84 stereo amp?

[@drtidrow]

What's driving the change? Note that a .022uF would work just as well as a .02uF one, and generally much easier to find... and with component tolerances being what they are, a cap marked as "0.02uF" might have its actual capacitance higher than one marked "0.022uF" Another option would be to put two 0.1uF caps in parallel, as capacitance adds in parallel.

[@stanleyyu2079]

Reducing the value of the coupling cap will likely reduce the base (low frequency).

[@garypamflett2150]

im due to do a recap soon . are coupling capacitors electrolytic or not ?? as i want to get this project right thanks .

[@drtidrow]

Hope your recap project came out okay, as this question is a year old now... generally, coupling caps are not electrolytic, as they tend to be "leakier" than foil caps to begin with.

[@dr.frankenstrat2076]

Are milivolts ok or zero volts on the other side?

[@drtidrow]

Depends on how the circuit is wired on the low-voltage side - a few dozen millivolts at the grid of a tube is fine, as long as the cathode voltage is an order of magnitude higher. For example, you might have a circuit with 10-15 millivolts on the grid, and 5-6 volts on the cathode... as long as the grid stays at a negative voltage relative to the cathode, you're generally safe.

[@gussuk11]

Your link for the PTFE tubing is no longer any good. Besides that I learned a lot from your video Thanks!

[@mikedunn7156]

After watching many techs that specialize in vintage electronics on you tube.I decided I want you to work on my marantz 2275. Where are you from. I’m from Long Island my. Do you have an email?

[@jameshorn7830]

You didn't replace the black cap in the upper left corner...

[@buildstoys]

.

[@daleburrell6273]

WHAT ABOUT THE "BUMBLEBEE" CAPACITOR IN THE TOP LEFT CORNER?!!

[@Blueglow]

Its not really a coupling cap, I'll replace it with an XY style but that's outside the scope of this video.

[@daleburrell6273]

@@Blueglow uh-huh...

[@mikesradiorepair]

As Mark states they are not coupling capacitors. If you look closely it is attached to the AC mains cord and in vintage gear is commonly referred to as the "death capacitor". If it shorts out it can energize the chassis by directly coupling the AC line to the metal chassis. Safety caps that go across the line or line to ground (chassis) capacitors are best replaced with modern XY rated safety capacitors that are specifically designed for this type of application. If these capacitors ever go bad they go bad open and not shorted.

[@oldestgamer]

Thanks Mike for that informative explanation!

[@Blueglow]

@@daleburrell6273 and now you know the real reason I didn't address it in the coupling cap video. kzbin.info/www/bejne/h2HNfmNrqN2saJo

[@inerlogic]

Outer foil is a subjective debate? Hook one of those unmarked yellow caps across your o-scope, grab the body with your fingers and tell me about how subjective the noise is....

[@chippsterstephens6800]

Odd you used vintage blue molded caps in the thumbnail, I have never seen one to show leakage at rated voltage, on a stancore capacitor analyzer, not one! Also the blue urs meter actually will read esr on low value caps. No issues with blue molded caps. The idea that you have here, to just shotgun replace caps in say a blackface fender with blue molded caps is one unwise , and degrades the value of the amps, it’s flat out not a leaky cap, I have yet to see one, other caps fall into your line of thinking, but not the blue caps, I have tested 100s and have about 60 left. Also cap heath is effected by use or non use, non use is the worst case, and old caps that have not been used in some time can show slight leakage electronically. Yet stop after properly formed, things like this are important in vintage gear. New is not just assumed better with vintage gear. Use or non use very much matters, and that just the physics of a cap. You should know that. I stopped watching at the point you said it did not matter.

[@noel3422]

Stoped at the outer foil coupling cap polarity thing being unimportant, what? Lol..