Those Wonder Caps might be replacements! What are the tube designations? Does the preamp work?
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Congratulations on acquiring a fine preamp! I expect you will get years of use from it! The 6922/ECC88's are an excellent choice for preamps/phono stages! Wide bandwidth and low distortion! Also no problem getting replacements - they had widespread industrial use in oscilloscopes. And still in current production - though I prefer older ones! The Russian military used them and those are the least expensive ones available - but still well-built and sounding fine. I might have some in my collection!
Thanks guys. I'm sure everything in this unit is old and it sounds like probably original. It was unused in the owner's home for years and then spent at least two or three years in a non-climate controlled basement.
Despite that it is completely clean inside and out and sounds wonderful.
I am unlikely to make any changes to tubes or caps unless something goes wrong. It sounds wonderful to my untrained ears so any changes as like as not would not be appreciated by me.
Here is a dumb question. I assume that replacing caps requires soldering...which I do....but very poorly. But do tubes need soldering or wiring? My old memories of tubes is that they simply plug in which would mean that tube replacement would only require removing the top cover, unplugging original tubes and plugging new ones in. So is tube replacement a DIY job?
I'm mainly asking is that with an old unit like this I assume they will fail at some point.
How do you know when they fail? Do you lose all function, just one channel??
Final dumb question, if one fails do you replace all 4?
You might want to get the filter capacitors replaced. These are not the film caps that have been mentioned so far.
The filter capacitors are electrolytic and after a couple of decades they are often failing. It is possible for their failure to also damage the power transformer, so its a good idea to replace them.
Audio research has a database of old equipment at arcdb.ws you can look up yours under line stage. It gives a little info on the unit and has a photo of the interior so you can see it better without taking the cover off. The wonder caps look original doesn’t look like the tubes are soldered. Perhaps you have already been to the site if so you can ignore this post.
This subject has been pretty well covered, so just additional affirmation from a former ARC LS16 owner:
To answer your question on replacing tubes... they simply pull out and you can replace them by gently pushing new ones in. Give them a little wiggle as you pull gently, and they should come right out.
If one fails, you don't need to replace all 4, but if you don't then you'll have a mismatch. The new one will operate at a higher level than the old one. You may or may not notice. I would replace in matched pairs, at least.
If it sounds fine, I would wait until one fails. You never know... the system may have only had a few hundred hours of use, and the tubes should last thousands of hours. Don't replace them just because they are old... you may end up spending money for nice NOS tubes when you already own good, usable vintage tubes.
You can get a new set of tubes from Upscale Audio. They're a little bit expensive but they have good quality tubes and if you contact them they will be very helpful. If you don't know how old the original tubes are, then it's a good idea to get a new set.
Leave the InfiniCaps alone. Audio Research gear is definitely not the equipment to learn DIY repairs or soldering skills.
Also, never change filter capacitors if the amplifier works. You'll know the power supply caps need replacement when the unit gives out a 120 hz hum or if you see physical damage (bulging top, orange goop indicating leaking electrolyte, dark colored deposits on the circuit board, things like that) .
And yes, the InfiniCaps are stock. AR also uses the expensive REL caps (the yellow ones) as standard equipment.
You have a nice little preamp there, with new tubes I don't see why it won't last you another ten years or so.
Lots of opinions. Ha! @atmasphere is right as usual in that it is best to replace those old electrolytic caps as a prudent preventive maintenance step. They are old and certainly have started to dry out with time.
Those coupling caps you mentioned are very easy to replace. Any good tech or experienced DIYer could do it within 30 minutes. You can do much better in SQ than those dated caps. Many good ones to choose from that will improve the sound quality nicely. No need to, but just a nice to upgrade in the future.