Electro Harmonix 6CA7
The 6CA7 tube is a beaming tetrode tube and commonly said is the American version of the classic EL34 tube. 6CA7's are also called EL34 fat bottle. They can replace usually any EL34 pentode because they have very similar electric characteristics. In my tube amplifiers power section are Electro Harmonix tubes from which I was not that excited in highs and lows as much as in excellent mids, of this tube. So I started searching for a tube with an extended frequency range, dynamics and energy. So once I came across the Electro Harmonix 6CA7 tubes for which I read all this characteristics I wanted. I made e search in ebay and I found a nice offer of a matched quad. I ordered them and in a week and a half time they arrived nicely packed.
Next move was a communication with Luxman international to ask them if my Luxman SQ-38U is compatible with this tube type. The answer was positive and then I asked them what I should do for the fixed bias of my amplifier and I got no answer. So I had to take some advice from a tube expert and I chose somebody who knows a lot. Tsakiridis Brothers owners and designers of Tsakirides Devices Company of tube products. They told me to just install them and run them. And this is what I did.
I turned on the amplifier waited for the start up delay relays of tube warm up and when the amp was ready I started some listening.
First impression was mixed. Great Dynamics I never could thing that my amp was capable of. Low frequency extension with excellent tonal of low end, performance, with body and fine lows articulation! Extended higs that were very transparent also with great tonal performance. But mids were transistor like sounding. This was my first objection. Mids no were a bit less musical an harmonics had a feeling of quick attenuation in time, plus swallower depth of soundstage but with larger width and height.. An hour later these characteristics gave their place to better behaviour. So after some discussions with tube friends I was advised to give an amount of 50 hours at least before making my mind and this is what I did again.
And they were right. Mid frequencies became more refined and transparent. Voices became more realistic and harmonics were rich creating a charming result. Great musicality with fine tonality across the whole spectrum. Great energy and dynamics creating the impression of a power solid state amplifier but with musicality and transparency. Excellent soundstage especially in depth creating a fine instrument positioning in depth. Excellent focusing of each musician in soundstage regardless of volume levels. Ok mids were not as musical as a great EL34 can do it, but more musical than a 6550 or KT88. Charming voices and instrument reproduction with transparency and lot of energy, providing any time an excellent dynamic behaviour.
Highly recommended if you want something extra from your EL34 amplifier!