I decided to do some tube rolling for the Indeed 6N3 Tube Buffer Amplifier and the 6N11 Tube Class A Headphone Amplifier.
For the 6N3 Tube Buffer Amplifier I changed the Sino 6N3 tube for a JAN-GE 5670W which is a mil-spec rugged version of the 5670 and is fully compatible to the 6N3 as a drop in replacement. In fact I have even higher hopes and have a Western Electric 2C51 which is also compatible but thought I would try the 5670 first. The GE 5670W as seen from the box was manufactured in March of 86.
The change of the 6N3 to the GE 5670 was so dramatic, it was like night and day. The Qinpu Q1 which is hooked up to this buffer immediately benefited and the sound was so sweet, resolution, detail and impact vastly improved and narrowed the gap with the Indeed Class A Headphone Amp. One can only imagine what the WE 2C51 would do, but I will find out soon. The cost for the upgrade is also low between 6 to 8 US$ and well worth the upgrade. But if you are thinking of the Western Electric 2C51 then this will set you back US$50.00.
Above photo: The 6N3 on left and the GE 5670W on right with box. The 5670W is a much shorter tube then the 6N3.
Below: The Western Electric 2C51 tube known as WE 396A.
For the 6N11 Tube Class A Headphone, the Sino 6N11 tube would be replaced by a JAN-Philips 6922 which is a mil-spec grade 6922 and also a direct drop in replacement for the 6N11 tube. The manufacture date for the 6922 was May, 87. So why the choice of the Philips 6922? The Philips 6922 low noise tube type was rated the "best buy" by Vacuum Tube Valley magazine in their 6DJ8 / 6922 tube showdown. Vacuum Tube Valley magazine cited a better bass end and "less offensive" high frequencies as two of the main reasons for their choice. Certainly once the 6N11 was replaced by this tube it was immediately apparent that the bass was even tighter and better controlled and resolution was even higher and more refined then before the change. Transients were much much better now with the 6922. The Jan-Philips 6922 is available as NOS for about US$20.00.
Above photo: The Philips low noise Jan 6922 on the right with box before rolling. The 6N11 and the 6922 are roughly the same size.