Has anyone had any experience with both, curious on thoughts regarding the differences. Not a purchase happening soon, just planning. This is to be used in conjunction with DS Sr and ATC SCM40 speakers.
Am slightly concerned with the amount of changes different tubes impart, if they are defective, heaters, life, etc.
Thanks in advance!
I can’t address the first part of your question: 350.8 vs. BHK250. As to your second concern about tubes, you have to decide what kind of ownership experience you want. Yes, a couple driver tubes in the BHK do slightly complicate long term ownership because you have be concerned about occasional replacement. However, in exchange for that, you gain the ability to fine tune the sound of your system. There is an undeniable additional level of realism that those tubes add to reproduction but only you can decide if the trade off of slight replacement hassles is worth it. Personally, I enjoy the ability to fine tune the sound of my amp as other aspects of my system evolve.
Hi Photon46,
Thanks so much for your reply. I guess my follow up question to you would be, once you find the tubes you like are they always the same when you put that brand and model back in or do you need to buy a big batch to ensure your sound doesn’t change when you have to replace your tubes?
Thanks,
Veneet
I have recently replaced the valves/tubes in my BHK250 with Telefunken PCC88 and love them so much I’m going to order another pair to keep in stock, this should see me for the next 5 years.
Veenet, Your question about tube manufacturing consistency is a good one and doesn’t have a simple answer in my experience. Different tube manufacturers have differing degrees of consistency and quality control, especially if we’re talking about tubes of recent manufacture. Recent manufacture tubes of Russian and Chinese origin can perhaps be more variable in quality control than American, European, and Japanese tubes manufactured in the 1940-50’s through 1970’s. That said, one’s best defense against possible unwanted quality variables is to buy from reputable tube vendors of long standing. Vintage Tube Services, Upscale Audio, Brent Jesse Recording (Audiotubes.com), Watford Valves, Langrex Valves, are some well regarded dealers that have good reputations. If you want to buy the best of modern manufacture tubes you can either buy replacements from the original equipment manufacturer or someone like Grant Audio or Upscale Audio who screens their inventory for duds.
Photon46,
Thanks again for the wealth of advice and info for working with tubes. It is really great to get the info from someone who knows! It’s very different than solid state, I will have to figure out what works best for me, I suppose I will have to travel and get an audition in!
Best regards,
Veneet
Veneet,
I’ve not done a 1-on-1 comparison, but here’s a suggestion for when the time comes. Both PS Audio and Reno Hi-Fi offer in-home trials. Return shipping on one of these behemoths will cost a bit, but the trade-off is a comparison in your own listening room in your own system. Priceless.
(Reno Hi-Fi deals in new, demo and used Pass equipment. I’ve dealt with them for over 20 years and Mark Sammut embodies PS Audio’s over-the-top customer service attitude. My own system is equal parts Pass and PS Audio.)
I’ve had both tube and SS preamps and amps over time. As SS got better and better, the differences to my ageing ears became less and less. I finally settled on Nelson Pass’ XA class A amps, which to me offer the best of both worlds. As a side benefit, my listening room is in a cool basement that benefits from a bit of auxiliary heat. 
That said, I sourced my electronics before PS Audio launched the BHK series, which are much easier on the checkbook. If I had it to do over, who knows? My Rx is to try them both.
HThaller,
That is great advice. I think you are right the only way to do it is a head-to-head comparison. The cost of returning at this price point is worth the comparison.
Thanks for the Reno HIFI suggestion too. Always happy to deal with customer service like that at PS Audio!
Best regards,
Veneet
Who amongst us have the dough and physical strength to compare the two in our systems? I am a happy owner of Pass Labs ax100.5s and could not imagine a better sound, paired with PS Audio source and preamp. I cannot financially consider the 100.8s, much less the 350.8s. Even if I could, in head to head listening sessions a few folks prefer the sound of the 100.5s to the 100.8s. I’m guessing the bigger amps have a slightly different tone than the smaller ones, good or bad. As always, system dependent. The 100.5s are like ovens in my living room and I imagine the 350.8s would be hell in the summer time, not to mention the increased electric bill. My ax100.5s are plenty of drive, even for my 7,000 cubic foot living room. In fact, they never clip and the power meters on them never move to the right of center, meaning they are never stressed even when I play music extremely loud with strong transients.
It would be interesting to hear from those who have had both the BHK 300 and Pass Labs in their systems. Both are fine amps and no doubt pair nicely with PS Audio products.
You know it’s kinda funny, I never thought about the heat issue. I am in Austin in an older house and my office is already an oven in the summer. I might actually have to make a decision based on heat!
Veneet,
There are two topographies in the Pass Labs lineup. The “X” series are class AB amps that are biased into Class A operation for the first 5-10 watts or so of power, after which they operate in class AB mode. These draw less wattage at idle and don’t put out heat like the “XA” series amps that joesphlg refers to. The X-xxx.8 amps superseded the X-xxx.5 amps.
The “XA” amps operate in Class A mode up to their rated power, so they draw their rated wattage even at idle. They do get toasty. As with the “X” series amps, there is an older XA-xxx.5 series and the current XA-xxx.8 series.
According to website specs, the X350.8 draws about three times as much wattage at idle than the BHK 250 (~500 watts vs 175), so I’d expect it to run warmer.
I worked my way up the Pass food chain over a period of years by buying and trading in used or demo equipment through Reno Hi-Fi (Mark will buy back / trade in any used Pass gear and makes a market for used Pass equipment). The XA .5’s sounded a bit more dynamic, with punchier bass. The XA .8’s were less so, but had greater transparency throughout the soundstage. So there are differences. Either way, they are really solid (and heavy) and sound gorgeous. Nelson could have designated the series as “OK” as in “OverKIll” or “BA” as in “BoatAnchor”
I have heard the BHK’s at the RMAF show in Denver, and in PS Audio’s Sound Room 1. They are no lightweights. either. Knowing how PS Audio and Pass voice their equipment, I don’t think you could go wrong either way.
Nelson Pass has an interesting white paper that touches on distortion and amplifier voicing here, if you’re interested: https://www.passlabs.com/press/audio-distortion-and-feedback
Long story short" “Anecdotally, it appears that preferences break out roughly into a third of customers liking 2nd harmonic types, a third liking 3rd harmonic, and the remainder liking neither or both. Customers have also been known to change their mind over a period of time.”
Have fun.
And if you really want to drive yourself nuts, also listen to the Pass XP-20 solid state, two chassis preamp. (Forget what you think you “know” about tubes/solid state.) I thought after 30 years of all tubes I knew.
Thanks Guys, and great info on the different series that they have. I think it stands to reason to still try both (and the preamps eventually!)
Veneet,
Not the BHK 250, but here is a review by Anthony Cordesman in TAS that compares the BHK 300’s to his reference Pass XA-160.8’s.
Spoiler alert: he keeps the the BHK’s as a second reference. (Must be nice to be able to do this) 
Here are some comparisons of xa100.5 and xa100.8, the 100s being considered by many the “sweet spot” of the xa product line.
http://www.audioshark.org/pass-labs-71/pass-xa-5-vs-xa-8-a-5103-page4.html
If I were buying new, I would probably buy the BHK300s taking advantage of PS Audio’s trade-in program. I like the tubed inputs and the flexibility they offer for fine tuning the sound.