This post turned out a bit long, but I hope it is helpful to future HA540 owners
Interesting that this has popped up recently, as I purchased an HA540 right about the time the thread was started.
First, I read every comment and post on the Internet about this amp (and tubes for it), which is not hard, as there is not that much. Bellari is made by Rolls, who make professional audio equipment, and so they don't publicize their gear through either Audiophile or Headphone circles. So, the amp has received very little attention, relative to say, Woo Audio or Bottlehead. However, I did notice that all the reviews were positive. Unfortunately, no one has compared the amp to any other amps - one review mentioned that he thought the amp sounded comparable to ones "costing several times as much", but never gave specifics. I was looking for something that was better than the Cmoy, and used tubes, but not as expensive as a Bottlehead or Woo, and the HA540 seems to be the only good choice that fits.
Second, there is a lot of gibberish on the Internet about using other tubes to substitute for 12AX7 tubes. There is one famous old article on another site promoting that idea, but which has been called into question by more than one tube expert. And, I have yet to hear one comment about using different tubes by anyone who knows anything about electrical engineering. In short, I think it is a bad idea, and an especially pointless one since there are more 12AX7 tubes available than any other type.
Terja mentioned using a different type in order to get "less gain", but other comments of his seemed to indicate that he was using the higher gain input (which confusing is called "low"). So, he could probably get the same result by just using the input marked "high" (which is what I use).
Anyway, after some researching, I tried two new production tubes:
- JJ 12AX7 ECC803S Gold-Pin cryo-treated from cryoset.com
- Tung-Sol 12AX7 ECC803S Gold-Pin cryo-treated from cryoset.com
In both cases, I chose that model not for anything about gold pins, but because they also have been pre-selected by the manufacturer to be higher quality.
I did not compare cryo-treated to non-cryo, but I did read several threads about it, and the differences described by several people seemed not to be imaginary. The difference in price is minor, and cryoset.com is a good supplier for tubes in general, so I just went with those. The idea was to give new production the best possible trial.
The result with the new production tubes (with at least 20 or more hours of burn-in on each), was that I found the supplied tube to have some "glare" or "screech". The JJ was definitely better in that regard, and in various other qualities (I have not yet done a definitive comparison between any two tubes, it is mostly my subjective impression so far - although I do have a set of tracks that I play each time I change tubes). I later found the Tung-Sol to be an improvement over the JJ.
However, I still found all three new production tubes to have some "glare" (I am using a Shure SRH-1840, so any screechy aspect is very apparement). So, I did more research on vintage tubes. A great site is:
http://www.audiotubes.com/12ax7.htm
(His prices - even for the lower cost items - are somewhat higher than what you find on ebay from reliable suppliers, but clearly you get premium service and carefully tested and selected tubes from him. But, the site is also a great resource for information very useful in investigating tubes you find elsewhere.)
The four vintage tubes that are constantly mentioned in a variety of threads on tubes are: Telefunken (made in Berlin), "Amperex" (made by Philips in Heerlen, Holland), Mullard (made in Blackburn, Great Britain), and RCA/Sylvania/G.E. (made in USA). The USA ones always have the qualifier "great value for the low price" or "surprisingly good in guitar amps", and so I decided to try one of each of the other three European tubes - because - the HA540 only needs one tube and so price is not as much of an issue as with amps that need four, six or eight tubes. (But I should point out that the best reviewed USA tube - the RCA "black plates" - costs no more than the above new production tubes, and might be better than any of them.)
The first vintage tube I tried was an Amperex 1970 12AX7A. The sound is definitely a step up from the new production tubes, and is without that glare. It has excellent bass, and generally a wide even bandwidth from low to high.
I then tried a Siemens 1961 OEM tube made in Munich, West Germany for "Capehart" - the first high end audio company in the USA (probably for their record player which used six 12AX7 tubes). The web site linked above recommends several "equal but cheaper" subsitutions, including Siemens as sounding very close and similar to the famous and pricey Telefunkens. And I have found the Siemens to be another step up over the Amperex, due to its very superior sounstaging and imaging. The Shure SRH-1840s are unusually good in that respect, and easily reproduced the exceptional "3D" sound of the Siemens. You can hear small movements of sound in all three directions, and instruments that produce a sound from many points do have a more three-dimensional sound. It's subtle and I think fragile - for example, a cheap headphone extension cord might be enough to make it vanish.
I also ordered a 1963 Mullard made in Blackburn in Great Britain, but that has not arrived yet (and it will probably be a week before I can add my impressions of that to this post or this thread).
When a component provides something that is missing otherwise, that is very compelling to me, so at this point, I am inclined to ratify the plurality of tube fans who feel that vintage West German tubes (usually as "Telefunken") provide the best possible sound quality.