Audio Research Tube AMP Reliability

Yes, Amperex. Some marked 'USA' and many marked PQ.

Well I havn't gotten in too many M-100 but if I do I know who to call...8o)

hi everyone!
here is the real story:
ARC gear that was produced in the 80s was the best ever made, period.
Problem: in those days premium hi fi parts with todays technologies where not available. Caps, resistors, volume pots, internal wiring, connectors, solder, plugs.
Huge progress in these areas made in the last 30 years.
If you have time ,money and basic skills, replacing above parts within ARC  gear of the time, will yeald incredible results.
As for tube supply, this is a big issue. Unless you own a tube tester, you are screwd.
NOS tubes are a gamble. Today's tubes  are best bet, provided you buy a large amount of the same production batch.
Here are some parts manufacturers: V caps, vandenhul wires, WBT connectors, TKD stepped attenuators (type C minimum), Caddocks tfts, vichay nude, Mills, fred diods.
Ps electolytic caps in ARC preamps must be replaced with polyprop
The sp10 has space on top and bottom of board to do so provided you lift the whole chassis. The 8s need an external box.
Hundreds of working hours, but then you have a killer, and W.Johnson will bless you from his other life. 

This is an old thread, but for what it is worth I owned an SP-6b and a D90 from 1980 until 2010 with zero problems.  I recently purchased an old, clapped out SP-6a and recapped it with Mundorfs ... sounds even better than my 6b did.