Changing capacitors in amplifiers etc

[Jez1234]

Split from this thread:-

https://www.vintage-radio.net/forum/...d.php?t=204116

Recapping amps is about the most common job I get asked to do. I always accept the work. Sometimes it is a waste of time but it's surprising how often it does in fact need doing. Miniature modern electrolytics that have been placed too close to heatsinks so the unit can fit a specific form factor can quite often fail, or be leaking electrolyte and on the verge of failure, (whilst the PCB is attacked by the electrolyte) after as little as 7 - 10 years in some models. The stupid fad of leaving hi fi switched on 24/7 (actually encouraged by certain manufacturers who no doubt expect a good income from their service depts) can decimate the electrolytics in just a few years and has at least been lucrative for me over the years... I tried many a time on hi fi forums to persuade people to switch the gear off but just got told repeatedly that the manufacturer says to never switch it off and that they trust the manufacturers opinion way more than they trust mine... you can lead a horse to water and all that... so I happily take their money to re-cap amps which often actually are on their last legs... and those that aren't but the customer insists they are!

One I did turn down was a guy with a NAD 3020 who told me that apparently wirewounds sound amazing and the reason cheap amps don't sound like £5K amps is that they are not built with entirely wirewound resistors and would I give him a quote to replace every resistor with a wirewound type. No was the answer. I've turned down many equally crazy requests such as replacing all the wiring with pure silver wire.

A few of my er... rivals actually advertise such nonsense as a service they offer or refer to something like "Grade one upgrade package includes rewiring with pure silver wire which takes performance to unbelievable levels and for only an extra £550" or whatever. No names no pack drill etc.

FWIW, when restoring the Solartron OS101 I wrote up in "Success Stories" I obviously tested all the electrolytics. One had been replaced some time after 1974, the year present on 3 Plessey 10uF caps in parallel replacing the original 32uF cap, but all the rest measured correct for capacitance and the ESR was actually considerably better than most brand new small electrolytics. The date on these huge-for-their-capacitance old timer TCC electrolytics is Feb 1952!! They don't make 'em like that anymore... but they do make 'em a hell of a lot smaller!

[Jez1234]

Erm... I'm rather confused here! I haven't the faintest idea why this was split from where it was relevant ie an ongoing discussion about recapping amps. I'm all ears if a mod would please explain.

[Station X]

The thread you originally posted in was specific to recapping a NAD 3020, not recapping in general. It was likely to drag the thread off topic and offered no help to the OP.

[Radio Wrangler]

But it is a generally useful piece of advice for those considering recapping and is likely to be seen by more of them than in a NAD3020-specific thread. Moving it to be the head of its own thread makes it more prominent to the people who could benefit from it.

The forum has a steady and distressing flow of "I've recapped it and now it doesn't work at all!" posts and something that might get them to think or ask before going ahead is the help they most need.

David

[Jez1234]

OK thanks mods.

[kalee20]

Originally Posted by Jez1234

One I did turn down was a guy with a NAD 3020 who told me that apparently wirewounds sound amazing and the reason cheap amps don't sound like £5K amps is that they are not built with entirely wirewound resistors and would I give him a quote to replace every resistor with a wirewound type. No was the answer.

I'm not sure where I'd get a 1 megohm WW resistor anyway, for my valve amp grid leaks... but I replaced the dial lamp shunt resistor in my Bush DAC90a with a wirewound, and it sounds superb!

As for capacitors, I'd say yes to waxies, to small electrolytics (unless hi-rel, epoxy end sealed), to large electrolyics that are bulging, and to any capacitor with a cracked case. There's sound engineering reasons at play there.

[trobbins]

I also check leakage at the voltage rating, as an indicator of health, and have happily left e-caps in situ from the 1960's if they test ok for C, ESR and leakage.

[Radio Wrangler]

Waxed paper capacitors are generally in the replace on sight category, but waxed silver-mica are probably OK. They are also usually in RF circuitry needing realignment after changing and need something of similar temperature coefficient so that realignment stays good over a range of temperature.

David