Caps and Tubes

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.

George,

 

This subject has been pretty well covered, so just additional affirmation from a former ARC LS16 owner:

 

1. The Wonder InfiniCaps™ are definitely stock.
2. The ARC Database is a wonderful reference tool but know it is not in any way affiliated with the Audio Research Corporation.
3. If you plan on keeping your LS16 for a while then another vote for atmasphere’s (always) sage advice. Have the filter capacitors replaced and consider it preventative maintenance.
4. Although not brought up, if you go looking for a phono preamplifier the ARC PH3 made an excellent and very synergistic combination with the LS16. The PH3 utilizes three 6922’s, same tube as your LS16.

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.