Sugden P128. Replacing Caps.

Hi all,



I'm replacing the capacitors and a few bad looking resistors in my Sugden P128 monoblocks.

Something I would like some clarification on is, should I replace the ceramic and tantalum caps or only if they show signs of failing? I'd obviously rather not have to but if it's recommended, I will.
Also should I reset the bias after recapping?



Regards,
Byron
 
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1/ Be careful. We see so many threads on here of damaged and blown equipment following a recap. It is so easy to get something wrong if you are replacing a bunch of parts. If you do it right and replace like for like there is no problem. All the issues are always man made.

2/ Old tants are/often/can be prime failure items. Personally I would definitely replace those.

3/ Ceramics should not normally need replacement although 'compressed disc types' can be failure prone on very rare occasions. Again, more to get wrong if you start changing a bunch of parts.

4/ Replacing caps will have no effect on the DC conditions. Whether the bias needs setting or whether an old and crusty trimmer has caused an incorrect setting is another issue. Either replace the trimmer and readjust (always from minimum bias) or measure the bias now and confirm its status.
 
I've given up trying to get good leaded tantalum capacitors. Where possible fit WIMA MKP2 or MKP4 film capacitors which in values up to a few µF can often fit in the same place as electrolytics. For larger values I use Elna Tonerex, Nichicon Fine Gold, or Elna Silmic II. Where a large value coupling capacitor is needed and there is little or no bias voltage across it (for example some input, output and interstage coupling capacitors), it is better to use bipolar electrolytics such as Nichicon Muse.

It's often not apreaciated that the capacitors used for feedback decoupling and onboard supply bypassing are handling audio signals, and the quality of these capacitors is just as significant as those used for coupling. The purpose of onboard supply bypass capacitors is to ensure that (±) rails are effectively audio ground, and audio grade capacitors should be used in those positions.
 
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I haven't bought a tant in decades tbh. Historically they were useful for low leakage current but modern electrolytics have improved a lot. Personally I would make a judgement call by studying the design to see whether other options were suitable. Only use a tant where nothing else will do.

Do you ever see tants in modern audio designs... not really. And tants are expensive.

When comparing electrolytics it is important to compare like with like when it comes to specs.

The lifetime is usually quoted at maximum ripple current and max temperature and so a 1000 hour rated part might well last decades when used more normally. Is the test done at 50/60Hz ripple or at some much higher frequency. Differences like that can really skew results and make one seem much better than another.

105C is the preferred choice these days (85C was the norm years ago). Low impedance on the face of it is good but isn't a primary consideration for this type of application. It is of more importance in high speed switching type power supplies where things like board layout is also optimized for high frequency high current use.

Any well known and well respected brands will be much better than anything fitted back in the day when the amps were first made.
 
Supply bypass caps typically carry non-linear (half-cycle) currents, so the quality is pretty irrelevant. What matters is the capacitance and ESR which determines the net attenuation they give to unwanted rail noise - in other words their job is to be low impedance, not linear.
Apart from power supply ripple as a result of circuit quiescent bias currents, they also carry ripple from the currents of the audio signal, after all that is what the power supply in an audio circuit exists for.
 
So these aren't good qualit? 199D476X9020E6V1E3 Vishay / Sprague | Mouser Australia


Also another question, when choosing an aluminium capacitor, apart from a good brand, what else should I go off? Is more life hours the better? And low impedance? It seems I can buy 10,000hr for not much more money. And also max temp rating I assume? Doesn't seem like there's much above 105° in-stock anyway, sadly.

There are many more choices for good quality capacitors for audio now than a few decades ago such that tantalum capacitors can normally be replaced with something more appropriate.

When choosing capacitors you need to realise that ratings from one manufacturer and not necessarily comparable to another's. And ratings like temperature, service life and voltage are interactive, meaning in the case of a power supply capacitor for example, choosing a voltage rating higher than actually needed might give much longer life than choosing a long life capacitor of just sufficient voltage rating, or that a capacitor run at a fraction of its ripple current rating is likely to outlast by several times a capacitor of a higher temperature rating running at its specified ripple current.
 
... We see so many threads on here of damaged and blown equipment following a recap. It is so easy to get something wrong if you are replacing a bunch of parts. If you do it right and replace like for like there is no problem. All the issues are always man made...

So true.
I just blew up my Valhalla, the power supply for my Linn LP12 turntable, twice. The dang thing requires 2 parts to be soldered on both sides of the PCB for continuity; if not, magic smoke guaranteed. Engineering at its very worst.
 
Its up to you. If you want it changing then I can add it.
Might as well, just put 'Sugden P128' at the start, thanks.




Well thanks for all the info and help everyone.
I don't have the expertise to study a circuit and ascertain what capacitor type would be suitable to replace a tantalum in eaches individual scenario.

I feel it is safer for me to just replace with new tantalums and up the voltage rating to improve life expectancy.


I will continue to see what I can work out over a couple days though.
 
So I've replaced all the caps bar one it's on backorder. I've replaced a few resistors. I figured I might as well check the quiescent current and DC offset. Offset was fine, sitting between 6-3mV. The QI was at 450-480mA! From what I can find out it's supposed to be set at 200-250mA. Could this big jump be caused by me replacing a few resistors? Or has this been set incorrectly in the passed?