PS Audio equipment chain all powered by P-10 regenerator.
DMP à DS Sr. à BHK Preamp à BHK 250 power amp à Polk Audio SDA SRS-2 speakers
PS Audio I2S, Grover Huffman XLR ICs, Grover Huffman speaker cables.
SR Blue fuses installed in DMP and BHK Preamp.
I initially upgraded from stock tubes to the BHK-recommended Tungsram 7DJ8 tubes (“platinum grade” and “cryoed” from Kevin Deal at Upscale Audio) in both BHK 250 and BHK preamp. Those have stayed in place for a year or more — so they are my “baseline.”
I have now auditioned Amperex 7308, Telefunken PC88 / 7DJ8, and lastly Telefunken E88CC / 6922 tubes (all “platinum grade” and “cryoed” from Kevin Deal at Upscale Audio) in the BHK preamp ( with the Tungsram 7DJ8 remaining in the BHK 250 amp for all these auditions ). Each set of new to me NOS preamp tubes was given ~ 80-100 hours prior to critical listening sessions, which included PS Audio “One” SACD, “The Quality of Silence” SACD by Steve Davis Project, Roxy Music “Avalon” SACD, Jimi Hendrix “Blues” CD, “Gob Iron” CD, Joni Mitchell “Hits” CD, etc.
All statements are “to my ears with my system.”
Amperex 7308 creates a very noticeable shift in energy balance – less energy in higher frequencies, but added some detail and “texture” to mids and bass compared to the Tungsram 7DJ8. Interesting sonics some may hear as an improvement. Probably blacker background/less noise than the Tungsram. Is this the source of the extra “texture” or is it more energy in the lower frequencies? Or both?
Telefunken PC88 / 7DJ8 (Upscale indicated these tubes as actually manufactured by Siemens) - gave a definitely more “vivid” presentation than the Amperex 7308, but with energy distribution perhaps more similar to Tungsram 7DJ8 than to the Amperex 7308.
Telefunken E88CC / 6922 — “Transformational.” “Another level.” I would even tell BHK himself I suspect he hasn’t heard his own creation to its full potential if he hasn’t heard the BHK Preamp with these tubes or similar installed. Dead quiet background – to my ears a “neutral” presentation , with greater detail at all frequencies but still very musical presentation like the Tungsrams. Increased soundstage in all dimensions (height, width, depth).
The Telefunken E88CC / 6922 are staying in the BHK preamp.
I am wondering what these tubes (Telefunken E88CC / 6922 ) will bring to the BHK 250 amp next down the chain. Is it possible that would create too much detail and thereby seem less “musical?” That remains to be heard.
I have ordered another set of Telefunken E88CC / 6922 to try in the BHK 250, or for backup.