I'm considering buying a 20 year old tube preamp. What's the approximate lifespan for electrolytics beyond which the price is too risking without a full recap? Would it be after 20 years on average when you can expect good quality electrolytics to start going bad in a tube preamp, or 30 years? Doing a risk assessment here based on your responses regarding probability ... the unit's fine right now ...
50 years ?
Electrolyts has no definitive lifetime, it's a combination of temperature ( which is low in most preamps), voltage margin and usage pattern.
When I restored my 70 years old Hammond C-2 organ last year, I was eager to replace all electrolytics in the AO-10 preamp. So I desoldered and, right before I was about to discard them immediately, measured them, just to find out they were all within their specs. They remained at their place.
Best regards!
Best regards!
If you buy it, just burn it in (if it has been in storage) and use it normally.
Replace capacitors only if they show bulging or leakage.
Most people bring an old piece up slowly on a variac. I just plug it in and replace whatever blows up. The choice is yours 🙂
Realistically, old caps dry out. I'd be more worried about the coupling caps from pre to power tubes. Those dry out and you have a red plating tube instead of a blown fuse/rectifier diode.
Realistically, old caps dry out. I'd be more worried about the coupling caps from pre to power tubes. Those dry out and you have a red plating tube instead of a blown fuse/rectifier diode.
Consider DC Link caps - high quality polypropylene in higher voltages, 500v upwards. Small rectangular sizes. Kemet, Vishay and others.
I find them smoother than electrolytics, and essential for cathode bypass caps. I use 40uf there.
I find them smoother than electrolytics, and essential for cathode bypass caps. I use 40uf there.
Panasonic who make some of the best electrolytics quote 15 years as the maximum life of their electrolytics in their data sheets because of the eventual degradation of
the rubber seals they say. They also quote an expected life in hours versus operating temp, the life gets shorter the higher the operating temp . So if in doubt look at the data
sheet if you can find it.
the rubber seals they say. They also quote an expected life in hours versus operating temp, the life gets shorter the higher the operating temp . So if in doubt look at the data
sheet if you can find it.
It depend on the quality of the capacitor and how it was use in the circuit.
To me, 20 years old is border line for the low quality capacitors (ex. Jamicon).
To me, 20 years old is border line for the low quality capacitors (ex. Jamicon).
I would never ever ever use an electrolytic coupling cap in a tube amp, regardless of how desperate I was to save money. 100 (or even 10) micro amps of leakage current may very well be in spec and be bad news.
Be warned that talking about capacitor "sound" opens lots of worm cans 😉
My take : no, "brand" is completely irrelevant, only measured parameters matter.
My take : no, "brand" is completely irrelevant, only measured parameters matter.
It's safe to say that low voltage electrolytics, for example, cathode bypass caps in early stages, should be replaced with better modern parts. A little effort, but no real money. Power supply aluminum can multiple caps are a tougher call for Golden Era amplifiers. Historians, like me, will argue that the originals should be carefully restored over a long period of time, and preserved, as possible. 6 or even 24 hours restoration is not impossible.
Others might say that modern Nichicon or similar 105C caps built into a new can, as Hayseed Hamfest does, is the better route long term. Can't argue with that either. If your piece isn't older than you, I'd recommend Hayseed Hamfest's cans without question.
All good fortune,
Chris
Others might say that modern Nichicon or similar 105C caps built into a new can, as Hayseed Hamfest does, is the better route long term. Can't argue with that either. If your piece isn't older than you, I'd recommend Hayseed Hamfest's cans without question.
All good fortune,
Chris
We need more info.
If using the cheapest available in a hot environment right at their voltage rating you'll want to replace them soon. If the builder decided to over spec temp, voltage, and buy from a legit source, theres a good chance they're fine to this day.
If using the cheapest available in a hot environment right at their voltage rating you'll want to replace them soon. If the builder decided to over spec temp, voltage, and buy from a legit source, theres a good chance they're fine to this day.
Chris,
admittedly that's exactly what I did with my Hammond C-2's AO-10 from above. I replaced all cathode bypass caps with modern ones, but kept the 70 yrs old PSU filter caps, as they measured fine, even with their ESR's. Hence, the organ's look with removed back panel keeps conserved.
Best regards!
Slightly, but there may also be slight differences depending on the voltage rating and the physical size of the cap. I found Vishay slightly leaner and Kemet slightly fuller. Small differences but I thought they were audible. I have a very minimalist and transparent 2 stage 2a3 SE amp and it enables you to hear the effect of various parts. I'm a huge fan of DC Link caps.
Funny, I use 1000uF to bypass a cathode. I use Aluminum Polymer caps like you find on a computer motherboard. No failures yet and no complaints.
No wonder, no fun. Aluminium electrolytics, regardless of which provenance, are the best one can do to AC bypass cathode resistors.
Best regards!
Best regards!