Thank you for your wonderfully eloquent descriptions of various valves sonic attributes and for being a pioneer introducing this fine headphone amplifier to the wider Head-Fi community.
OK. So no waiting until the weekend!
I have spent a very enjoyable hour and a half swapping between the GE 1U4's and the Mullard 1T4's. Let me say right of the bat that both are excellent tubes and in their own ways excel, it just comes down to what is more important to you as an overall musical presentation.
The Mullards start with a minus point as they are a little microphonic, no where near as bad as the Sylvanias but a gentle tap on the sides of the case will illicit a slight tinging sound. Now, this is largely irrelevant when listening to music as it cannot be heard.
Also, fit and finish of the Mullards is a little worse than the GE's,
The GE's are absolutely silent, one can knock hard on the sides of the case and nothing. Likewise they have exceptional build quality.
Now, to the sound.
The Mullards have that traditional romantic, euphonic sound signature. Immediately it draws one in as it is friendly and warming to listen to, Bass notes are stronger and are delivered with a more romantic than factual presentation. Initial listening had these as my favourites as it just sounded so lovely. Treble extension is lessened and the sound of wooden drumstick on cymbals felt larger than life.
All of this seemed lovely, I was really enjoying it and then it came to plug in the GE's
Now, The GE's have more bass weight than the Brimars but initial listening right after the Mullards left one feeling that some of the warmth and coziness had been taken away, it felt less inviting and enveloping, it felt like there was less bass. Treble extension just went on and on but is clean and no grain.
With the Mullards notes seem to keep going on and on never seeming to decay but rather smear into the next note, this on initial listening sounded great. The GE's on the other had start and stop on a pin. There is only decay of a note where it is actually present in the recording. If it is not there the GE's won't make it up, this initially felt a little cold and sudden. Guitar sounded more euphonic with the Mullards, more romantic where as with the GE's there was more definition to the notes played, more texture and detail.
However, after repeated swapping of tubes between tracks ( I used September in Montreal by Anne Bisson and from Steve Davis's quality of silence album one two free and infant eyes) the GE's started to move ahead in terms of musicality and involvement. I found that once the romance faded from the Mullards I kept preferring the directness of the GE's but to put it in context it was a diplomatic directness rather than a strict one.
Though the GE's lack bass weight bass is not lacking, rather the texture of the bass is revealed more than the Mullards making it in the long run far more involving to listen to the GE's than the Mullards as one could hear all the details but not at the expense of warmth or musicality where as the Mullards are all about warmth and musicality at the cost of detail and texture.
So, overall the GE's are ahead for me as they combine speed, accuracy and detail with musicality and warmth. Drum sticks on cymbals sound like wood hitting metal and felt in proportion. Notes decay as they should rather than as a work of fiction. Texture and detail are outstanding with the GE's digging deep into the mix and retrieving everything but not in a tiring way and not in such a way that all you end up doing is listening to detail. No, the GE's are holistic in their approach to reproducing music and combined with the Mullards in the power stage where you want some grunt and oomph this so far is my favourite all round pairing.
Over the weekend I will try the Brimars again and report back.
For reference I used my Piano Forte's solely
As far as the amp goes, well, great tubes make this amp even greater, this does not sound like a portable amp. In fact I keep coming back to my reference in pre amps when I think of this amp, the Nagra PL-P. That is another class A battery operated amp and with the combination of tubes that I prefer this comes as close as I have heard to that wonderful amp and higher praise I could not give!