On Friday, November 9, 2018 at 1:56:53 PM UTC-5, wrote:

Tubes are a whole 'nuther thing. It looks like there is a lot to
learn about tubes. How specific types work, which can be substituted
for which, etc. Which are best in new production because NOS tubes may
not be any good. And are often more expensive anyway.
Any more advice and suggestions are welcome.

Eric:

Yes, tubes are a whole 'nuther' thing - but at the same time, they are remarkably simple in their behavior. A few cautions:
a) Tube based equipment runs at much higher operating voltages than transistor-based equipment, most of the time. So you choose to use tubes, and you choose to do your own servicing, restoration and repairs (again and remember - these are mostly simple beasts), you will have to include an order-of-magnitude level higher in bench precautions and care. An isolation transformer is a mandate, as well as the correct understanding of its use. And so forth.
b) Whereas tubes are quite simple, they can fail in the most spectacular manner such that a certain amount of basic understanding of whatever is being repaired is required. Otherwise, the destruction of a transformer or worse could result - and that could be expensive, fatal (to the equipment) or both.

Thrift-shop/Estate-Sale equipment: I would not hesitate to purchase equipment from such sources, but only those items that are supported in the after-market. Name brands such as Fisher, Scott, Sherwood, Dynaco, McIntosh, even Stromberg-Carlson and, rarely tube Marantz are all fair game. But, some of the off-brands or large name-brands such as RCA, Zenith, and such would be problematic (but not impossible), and likely take more effort than they are worth at the end of the process. Those of us with a fairly large inventory of tubes, parts and pieces have a much different attitude than those starting off in this aspect of the hobby, where everything is a 'search'. Keep that in mind.

On tubes: Back in the day, makers such as RCA, Sylvania and others would turn out more tubes in a week than worldwide present production likely turns out in a year, and equally likely, reject the equivalent of present production monthly. I have active power-pentodes with tens of thousands of hours on them that still test well and hold bias quite nicely. I am hearing that getting 4,000 hours out of a present-day tube is 'good'.

NOS/Legacy tubes are not hard to get. Were it not for hoarding, I doubt there would be any shortage of any tube for any reason. I have (hiding somewhere) about 15 7199s, and no less than 16 1L6 tubes. All acquired over the years from garage sales, hamfests, and box-O-tubes auction purchases. Similarly, Euro and exotic tubes. Point being that I would not avoid anything for that reason, unless you are looking for a 50, or a 6T5.

On speakers: This is a function of efficiency, nature of the speaker, room size and other physical parameters. For my entire audio life, I have kept AR speakers, and at-present run 5 pairs of ARs, one pair of Maggies and one pair of Dynaco speakers. Of those eight pairs, three (all AR) are driven by tubes, including a pair AR3a speakers in a moderate room driven by a Scott LK150. Then the office system (AR Athena, Dynaco ST35) and work-room system (AR4x, Dynaco ST70). But for the Maggies, I use a brute-force solid-state device as even the big Scott would not be able to manage them in the room they are in. Point being that if you are not into ear-bleed volumes, and you are not listening in a very large room, most speakers would be just fine with most decent tube amps.

Amp Power & Clipping: A few brute facts. My most efficient speaker is 87dB at 1 watt at 1 meter.

97dB (twice as loud) would need 10 watts. This is a 10dB peak-to-average - about what is used by, at the two extremes, heavy metal and Gregorian Chant..
107dB (Twice as loud again) would need 100 watts. This is a 20dB peak-to-average, about that of well-recorded orchestral music as well as some classic rock, folk and bluegrass.
117dB - you get the picture. 1,000 watts. I have a couple of recordings that go here - the Saint-Saens Organ Symphony is one (1).

My solid-state brute-force amp is entirely capable of a 1,000 watt peak, as well as 200 sustained watts - and my speakers are perfectly happy with the former, but not the latter. However!! Solid-state amps (some, even most) if driven to clipping too much, do not 'play nice' with most speakers. A tube amp clips softly - much less chance of speaker damage. Bottom line, most situations, most speakers, most amps and if the user is reasonable, everything will be fine. It is at the edges where one moves into risky territory.

If you are going to "do legacy", I would focus on Dynaco, Sherwood/Scott/Fisher), and then everything else in that order. All of those names are well-supported, parts are available, and there is nothing exotic about any of them.

New, I would focus on VTA (tubes4hifi) first and foremost.

Best of luck.

Peter Wieck
Melrose Park, PA