We have noticed some discussion on using various tubes in AVA equipment, particularly Mullards. We decided to try some different tubes ourselves to see what we liked best. What follows is the results we found. Please note that we tried a couple of the tubes we have been hearing about, but have not tried "every" brand available; rather, we took a sampling of tubes to see what we could hear. There are other tubes that people are using that will undoubtedly have characteristics different than the ones we tried.
One of the basic things we aim for in designing audio equipment is to accurately reproduce the sound as it was recorded. We don't want to shape, modify or alter the sound. We don't design our equipment to work better with brighter speakers, or duller speakers. We don't design our systems to have a warm sound, or a cool sound, only to be as accurate as possible.
The same rule holds true in our solid state OmegaStar series, our tube/hybrid Transcendence Six, and our FetValve/Transcendence 7 equipment. The underlying technologies of each, however, dictate how far we can go in reaching total accuracy. We do not, however, limit our engineering in any one product line in favor of another. Simply stated we strive to bring you the best product at a very reasonable price.
Please note that we understand that people like different sounds and that a particular brand(s) of tube gives them the sounds they like. We have NO problem with that! We also know that people have a variety of equipment and speakers. Further, we understand that speakers have a character of their own, some may be bright, some lacking lows, etcetera, and that tubes can help in shaping the sound to a person's liking.
With all this in mind, here is what we found in our reference system consisting of a Transcendence DAC, Transcendence 7 preamp, FetValve power amp, and Biro L/1 speakers:
This is the stock tube we have been using since we introduced the Transcendence 7 last year. The EH is the most transparent and neutral tube of the batch. The midrange is very clear, dynamic, and transparent, without an overly warm "tube" sound. The bass is controlled and reaches nicely. The highs are good and clean with no edge. The midrange micro dynamics are very good. The EH has the least amount of coloring.
This new old stock (NOS) tube has a warmer "tube" sound. The midrange sounds were very lush and generally pleasing. There was a loss of bass control, with the lows not extending as far as the Electro Harmonix. The highs also didn't reach as well as the EH. The midrange micro dynamics were good. For those looking for a more romantic or warmer sound sometimes associated with tubes this is appears to be a good choice.
Mullard 12AT7 / CV4024:
The NOS CV4024 Mullard was our least favorite tube. The overall sound was shallow, with a significant loss of transparency over the Electro-Harmonix. There was a loss of bass control and reach. The sound has an overall brightness that bordered on steely and harsh. Most important was a big loss of micro dynamics in the mids which resulted in the shallow sound.
Mullard 6201 (gold pin):
The Mullard 6201, also a NOS tube, has a bit of the warmer tube sound. The mids had good micro dynamics, but there was a bit of lifting in the upper mids. There was also a bit of loss in the bass. The 6201 was a good tube, but for the "tube" sound we preferred the Amperex.
Philips JAN 12AT7 NOS:
We did not test this tube in comparison with the Mullards or Amperex, but we have compared it in the past with the Electro-Harmonix. The Philips lacked a lot in detail. The transparency of the tube was significantly less than the EH. There was a loss of both the lows and the highs. We found the Philips JAN to lack too much detail.
Note that the use of a particular brand of tube may give you different results depending on other hardware and speakers. For example, if your speakers are a bit soft sounding in the highs a tube like the Mullard CV4024, which tends (at least the ones we tried) to be bright, may give you good sound.
An interesting note: Both the Mullard tubes had a strange startup. When the power was first applied to the tube the filament of the tube glowed very bright for an instant before settling down to the normal luminance. I have seen this in the past with tubes in other electronics. I'm not sure what negative things this is doing to the tube, but it might be possible that the service life filament may be shortened.
Based on our testing we liked the Electro-Harmonix tubes the best because they are the most transparent and offer the least amount of coloration. We felt the EH stayed the closest to the source.
We also know that some people like the soft romantic "tube" sound. After evaluating the tubes we have decided to offer the NOS Amperex 12AT7 for those that want the tube sound. We felt the Amperex had the best micro dynamics outside of the Electro-Harmonix. While there was a loss in transparency, and the lows and highs didn't reach as far, we found the sound properly balanced and very easy to listen to.
If you place an order for one of our tubed products you can select either the Electro-Harmonix 12AT7 or the Amperex 12AT7 tubes. Please note, however, that the Amperex tubes are new old stock and we will offer them as long as the stock is available.
As stated above this was not a test of all the possible combinations of tubes. It is not our intention to alienate one brand of tube over another or to discount the experience people are having with a particular tube. We fully agree that tubes have a different sound and that each person has his or her preferences. Our goal was to identify a tube that allows our customers a warmer tube sound if they want it.
Thank you for your interest in Audio by Van Alstine products!!