General question about restoring a vintage amplifier

Discussion in 'Solid State' started by hc167, Jun 18, 2009.

  1. hc167

    hc167 Active Member

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    hi:

    I have some general question about restoring a vintage amplifier for long term usage. suppose I have a working vintage amplifier. I guess I would do recapping. So when we do recapping. we only need to replace all the electrolytic capacitors only? what about other such as cermic disc capacitor? I know that almost nobody replace film capacitor unless they want to upgrade to some kind of cap like auricap. Why people usually only replace electrolytic capacitor but not other.

    Second question. Why people usually do not replace the power transistors (maybe I should say transistor in general) since new transistor has better SPEC than those that was make in the old day. What is the reason for that? I found that people usually do not replaced them unless it is necessary.

    when we need to replace a power transistor. I did not see any people talk about they need to be matched. So when we replace power transistor, do we need to match them?

    When we replace the power supply filter cap. there are some people put a small resistor between the two pole of the power supply capacitor to remove the energy that is stored in the cap when the amp is shut off. however, there are also some people put a small capacitor (like 1uF file cap) between the two pole. what is the purpose of this small cap? and what happen if I put both the small cap and the resistor??

    thanks a lot
     
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  2. thisOne

    thisOne Listen...

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    let's say you were to do all that to a vintage amp (replace all caps, transistors, power supply, etc). with modern (better spec?) components, would it still be a vintage amp with its vintage sound or would it be a home made amplifier - and then, having done all that replacement..., why not just get the "today's" version of the amp.

    Is there a difference between the vintage MC 275 and the reissue?

    Is there a difference between a Marantz 9 and the reissue (or Marantz 7C and the reissue, for that matter?)

    Some would say there is, and some would pay more for the vintage unit that they would pay for a similar unit (with similar specs) made "today"
     
  3. dshoaf

    dshoaf That high voltage buzz

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    If you have a 20+ year old amp, then addressing long-term reliability and safety are important, IMHO. Here's the priority:

    - Safety first: Electrolytics dry out over time. The once-wet electrolyte dries out and the mass of plate metals and electrolyte begin to act like a resistor. If the cap has been sealed - most are - then the heat generated creates pressure which at some point will cause the cap to explode. Not cool! This applies primarily to the bigger filter caps in either tube or SS amps. Tube amp filter caps will let go with lots of flare, noise and perhaps flames. Not cool!

    - Sonic quality: For the same drying-out problem above, replacement of electrolytic caps that couple the various stages together will help return the amp to its original sonic glory. The brands of caps are a matter of personal preference and everybody will have a different preference!

    - Tube amps only: Tube bias circuits generally will have one or more filter caps in them, too. These also need replacement as a stable and reliable bias voltage to the output tubes is important for amp stability and to keep the output tubes from 'turning on', which runs too much current through the output transformer windings, heating them up and, worse case, causing you to have to consider a rewinding job. Very expensive when it can be avoided with prudent replacement of the proper parts.

    As for ceramic or other types of caps, yes those _may_ need to be replaced but the decision is more about whether there are known problems. You'll likely encounter folks here who have experience with a specific amp's needs in this case. You'll need to supply more details about the amp you have in mind for more help.

    Cheers,

    David
     
  4. hc167

    hc167 Active Member

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    I am not sure what you said would make sense. maybe I always assume that better components will always produce a better sound. in this case. replacing all transistors with better SPEC transistors will produce the sound that is better than the original vintage sound. right??

    I think one reason why people like vintage amplifier is because that was the amplifier where people think serious about the sound quality from the circuit design point of view and it is more affordable than the new one that cost more than $3000. Well, at least that is the case for SS amp, that is the way how it is. right?

     
  5. merrylander

    merrylander AK Member

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    Then there are some people like myself who wonder how a hermetically sealed capacitor can dry out and still meet the ESR test. There are four TOTL Yamahas working here in separate systems that have only had caps changed if they failed an ESR test. Except for the CR-2040, on that one I changed all the caps in the audio path looking for that wondrous improvement in sound - waste of time and money except it proved to my satisfaction there is still snake oil being sold.
     
  6. dspear99ca

    dspear99ca Super Member

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    Electrolytic caps contain liquid, which tends to dry out over decades of use. Other types of capacitor do not and as such tend to last indefinitely.

    If it ain't broke, don't fix it. Do you want a vintage amp or do you want a brand new amp? The vintage sound you are seeking may just be caused by those old transistors. As well, older output devices in TO-3 packages are no longer available at the fast F(t) of older ones. My Technics has 60MHz transistors and the closes I can come using new ones is about 1/10th that.

    If it's a push-pull amp, they need to be matched. If it's quasi-complementary they do not.

    The small-value cap to ground (bypass cap) shunts high-frequency noise on the power supply rail to ground.
     

     

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  7. hc167

    hc167 Active Member

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    I guess leave the transistors alone make sense since we want the characteristic of the vintage transistor sound. I guess just like tube amp where someone prefer tube "A" whereas, some other prefer tube "B" for the same circuit. I guess the same is ture for resistors since the old day carbon film resistors are being used most of the time and I was told that those resistors produce smoother sound.

    So for power supply filter cap, I guess it is always good idea to put a small value cap and a large value resistor (somethine like 3.3K) in parallel to get cleaner power and protect the power supply filter cap. right?
     
  8. dspear99ca

    dspear99ca Super Member

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    Bingo. The quality of transistors used in equipement from the mid-70's on is every bit as good as today as far as performance goes... sure you may find some slightly lower noise ones for your phono stage but it's splitting hairs... you probably won't notice any difference. As far as resistors go, I do not believe any resistors in any positions other than the signal path are going to make a shit's worth of difference to the sound, carbon composition or wirewound or cubic zirconium-encrusted titanium. It is just my opinion, I also don't believe that ultra-expensive interconnects or space-age anti-vibration mats work either, maybe my ears are too old to hear a difference or maybe I'm just not in a position financially to spend thousands on these things. Someday if my ship comes in maybe my opinion will change.

    Capacitor yes, resistor I wouldn't bother. The voltages in a SS amp won't hurt you like tubed equipment, and 63 or 80V caps can be discharged easily if you need to work on the amp. Otherwise you're just wasting power.
     
  9. hc167

    hc167 Active Member

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    I personally do not believe that expensive interconnects cable or something in that nature can have obvious improvement in sound quality (well, maybe with very good equipement). However, I do find that replacing electrolytic cap with good quality such as Black Gate does improve a lot in sound stage. That is why I raised such question or what other cap we can/should replace. The objective of replacing Electrolytic cap for an vintage amplifier is electrolytic go bad after many year of used. replacing it will only restore the amp to the original sound. and during the process or replacement, some people use those high end cap to improve the sound such as black gate, or Elna Cerafine cap. my question is, other than the Electrolytic cap, what other cap we can replace to improve sound quality? I know there are some people who ever replace some resistor to improve the sound quality. Just curious if this will vreate obvious sound improvement.
     
  10. dspear99ca

    dspear99ca Super Member

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    If they will physically fit and if you can afford it, get rid of any electrolytics in the signal path. Replace them with good-quality film caps or, if available and in your budget, PIO or other such esoteric uber-caps. If you follow the tube equipment forums here and on AudioAsylum, you'll hear people wax poetic about K40's, Vitamin Q's, Teflon caps, exotic Russian military caps, etc. and how they drastically change the sound. Maybe they do change the sound, but it'll be way way out on the flat part of the return-vs-investment curve. I find that Orange Drop 716's, even 715's do great for me, or the black Solens, for coupling caps. It's said that polypropylene and polystyrene caps impart a harshness to the sound, but they're REALLY cheap and you can try it and see.

    Overall with the exception of aging electrolytics you're not going to hear huge changes by changing out caps in a SS amp.

    Dave
     
    Last edited: Jun 18, 2009
  11. hc167

    hc167 Active Member

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    I forgot to ask this. what would be the ideal cap value for putting a small cap between two poles of the power supply filter capacitor?
     

     

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  12. dspear99ca

    dspear99ca Super Member

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    0.1uF will work fine.
     
  13. MaxSeven

    MaxSeven Word Skeptic

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    Agreed and a brilliant paragraph. No need to recap, unless your looking to kill some time, improve your soldering skills and spend some money.
     
  14. ConradH

    ConradH Addicted Member

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    That's also my belief, that if you measure esr every few years, caps will let you know well in advance if they're going to fail. I have a lot of equipment running 40+ year old caps with no problem. Now, if all you have is a cap meter with no dissipation factor or esr display, all bets are off. Also, HV equipment with tubes may not be so forgiving as it ages, and the consequences of failures can be more exciting or more expensive, so it pays to be a bit conservative on cap life.

    As for replacing everything you can with film caps, that will almost certainly change the sound, and not always for the better. Without a schematic and some knowledge of circuitry, you risk oscillation and waveform discrepancies. If you like vintage sound, stick with the original design when you change parts. That said, in a new design electrolytics are probably to be avoided. In fact, new designs tend to use far fewer caps in general than old designs because so much more is direct coupled.
     
  15. master_fo

    master_fo New Member

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    @merrylander : did you measure the caps you took out of CR2040?
    I am tempted to recap at least the phono stage - there seem to be lot of caps in the signal path. When I recapped my KEF Cantata speakers, all caps were off by at least 15%, and smallest were off up to 300%.
    CR-2040 probably runs hotter than the speaker crossover, so I would definitely expect some drift here. Since this is the only place in the receivers's signal path where caps are actually forming frequency responce, I am definitely inclined to check.
    But it your experience was that all caps there were within 10-15%, I would surely hold my horses :)

     
  16. savatage1973

    savatage1973 Addicted Member

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    300% is definitely an issue, but 15% not so much, since a lot of gear from the 70's and 80's used components rated at +/- 20% anyways, so they are technically still in spec.
     

     

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  17. master_fo

    master_fo New Member

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    Agreed - though crossovers are definitely one of the places exact value matters the most, and Cantatas were KEF's high end at the time, so I would guess they were originally +-5% max.
     

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