Is this the amp you are looking at?
I can't offer first hand experience but heres my .02...
>Solid Ebay history, 1000s of transactions for tubes and guitar amps... all positive. thumbs up on that.
>Ask him for pics of the internals. P2P craftsmanship can vary greatly. Theres some very shoddy/sloppy work out there that many (even the most experienced) builders hide under nice case-work.
>Ask him what volume pot he's using, there are some bad ones out there that have very poor channel balance characteristics at lower volume settings. This is more important if you are a low volume listener.
>Ask him what output coupling capacitors he is using, why he chose those and why he chose values he is using. This is one of the key elements to OTL amp design that experienced builders tinker and tweek with, it can have a dramatic impact on the sonic qualities of the circuit. Any "professional" experienced headphone amp builder will have given at least some train of thought to component selection at this critical stage in the circuit.
>Ask him for a schematic. I would never buy someones DIY tube amp without one, or at the very least a URL link to a schematic. P2P tube amps are fun little buggers. The ability to repair and service them is a big bonus over SMT/PCBA designs. You lose that bonus/perk to some degree without a schematic.
>He doesn't say it specifically what the Primary Vin is... 220 or 110... you'll need to confirm this, and its NOT something that should just be assumed.
>Most importantly you should inquire what power transformer he is using, and how its employed in the transformation. If the transformer is a dual primary, and he is using one of those primaries as the secondary... Thats a HUGE red flag, a UL violation... but most importantly its a fire and safety hazard. I don't mean to be an alarmist, but there have been some questionable circuits out there... parading to be high end, yet failing this most basic fundamental. (David Yee audio and Singlepower come to mind immediately).
>This statement caught my attention "using the leads of the components as far as possible to minimize the need of connecting wires." Cutting, trimming, component termination and wire routing (done cleanly) is one of the elements I look for in a quality P2P build. Its not an easy skill to master. Some builders have a talent for it, most don't. Cleanly routed signals is one of the things you are paying for when you purchase a well made P2P circuit from an experienced builder.
>His RCA inputs run through an A/B splitter switch. Ask him if its a triple pole dual throw (3PDT) switch, where he's switching the input grounds as well as the + signals. If he's only switching the + signals (DPDT) and common grounding all the "-" inputs, thats a red flag as this kind of circuit design can introduce ground loop noise on the inputs, depending on the overall "noise" environment around you.
These are all what I would consider very basic headphone tube amp fundamentals. If he can't reply back with these questions answered, or simply refuses too outright... keep your $$ and walk away. Its not like he's the only gig in town.
No experience with those tubes specifically, but his choice for driver tube is very common and inexpensive... thumbs up for that. The output tubes are somewhat more rare / difficult to source... but not impossible.
Edited by kramer5150 - 5/11/14 at 10:50am