December 8, 2025
#528
Gentle reader,
This article comprises Part Two of this article: The Robb Collections: Klipsch RB-35 RC-25 Speakers Plus OPPO BDP-93 Blu-ray SACD Player 6-Channel SACD at Last!
"Tube rolling refers to the practice of swapping out vacuum tubes in a tube amplifier to modify and enhance the sound characteristics. This technique allows users to experiment with different types of tubes to achieve their desired audio quality."
There is a lot of positive things which can be said about the Chinese people. They are very creative and capable as to creating and building all kinds of things. Far exceeding the rest of the world in many ways, such as the number of magnificent bridges they have built, for example. Especially so creating electronics.
I first wrote about the new Douk Audio (Nobsound) line of tube preamplifiers and power amplifiers back in September. All of which (preamps and power amps) are made on the same chassis here: The Robb Collections: World Premiere Review of Douk Audio's Exciting new Class A DJ587 Tube Stereo Power Amplifier!
This is a factory photo of what comes in the box of the DJ587 power amplifier. All five tubes, are of Chinese manufacture, of course.
Aside from a single tube cheap (likely Chinese) headphone amplifier I had found on eBay years ago and a small "Tube Buffer" amplifier which Bob B got for Bruce and I...
in which I DID try swapping the tubes...
a pair of these which came in these boxes..
and some of these new-old-stock U.S.A. made tubes...
In buyer's reviews of these Douk Audio (Nobsound) Chinese tube amplifiers many recommend trying other tubes in them. Either new-old-stock U.S.A. tubes. Or, Soviet-era tubes. So, I began looking on eBay.
Then this happened! The Robb Collections: Having Friends Who Are Neighbors is a Wonderful Thing! Gifted Klipsch Speakers And More.
To give you a better idea just how HUGE the organ is, see that tiny person standing in the center opening, above? That is Anna Lapwood, who IS petite, but compared to her organ she is microscopic. That being said, don't worry too much about how low your speakers can reach into the bass. 99% of the music you might play will never reach down to 20 hertz. So, save your money.
I bought a pair of these Soviet made tubes, which are "6P1P 6P1 Matched Pair Svetlana Tubes" via eBay.
And a pair of these too which are "VOSKHOD ROCKET" Soviet 6N2P-EV units, also via eBay.
(These three images are copyright of the sellers.)
The central tube, (seen below) between the two larger tubes on the right, acts as a rectifier. Thus, I thought it may not affect the sound. If I am incorrect, let me know in the comments.
While I have not run the amp for very long yet with the new tubes, the sound seems much fuller, as if it is higher and wider. The music sounds more realistic and crisp as well. 
This image and two below, show the Klipsch RB-35 speakers in place mounted atop the Dynaco A25XL units. I secured them with QUAKE HOLD!™ Museum Putty. It's a reusable adhesive.
If you have not read one of my Audio Articles lately, my system has gone through some power amplifier issues. What you see in the center of the image lower down (bottom to top) are my 1990's B&K Components ST1400 power amplifier. It had an issue in which the left channel was staticky. Atop it sits the Douk Audio DJ587 tube power amp. 
I bought a "Factory Refreshed" Marantz MM7025 power amp for 2/3rds of new price from Best Buy. I reviewed it here: The Robb Collections: Review of Marantz MM7025, their Last Two Channel Power Amplifier.
Once I troubleshot the B&K amp, I found one of the 30+ years old internal fuses blown. Since none of these power amps have more than one pair of outlet terminals, I could no longer enjoy my fifty years old Dynaco A25XL speakers. So, I put the B&K on the floor. Then, I saw how inexpensive these Chinese amps are via eBay US Sellers (well under $300USD) and bought the one you see. I was then using it to drive the Dynacos instead of the B&K unit.
These Klipsch are SO efficient and easy to drive, a pair of them was ideal to drive by the Chinese power amplifier which only puts out four watts per channel. It is Class A, which means it is on all of the time.
The one problem with this location of these amplifiers is that I easily (and without noticing) turn on the B&K power amp with the side of my foot when I walk by it.
I found another vintage Radio Shack Realistic APM-300 which you can just see sitting underneath the tube amp, above. I replaced the amp's tiny rubber feet it came with with much taller and way thicker rubber ones which clear the meter's height and allow airflow beneath the tube amp.
And, at last, here is the trifecta of clean, low cost (the speakers were free) efficient Class A sound. I have watched the power meter LEDs, (the scale can be set 0 to 2 watts or 0 to 200 watts) when the LEDs are bouncing towards the 2 watt level, the music is so loud I have to quickly turn it down! It's just too loud.
To sum up, while "More Power!" is the mantra for some things, our car engines, for example, there is another way. Look for and try the most efficient speakers you can find. Look for the maker's web site to find their specifications.
The terms "Sensitivity" and "Efficiency" are sometimes interchanged when it comes to speakers. These particular Klipsch models when tested in an anechoic chamber (below)
when driven by amplifier output voltage of 2.83 volts (=1 watt), their output produced a 96 decibel tone when measured from one meter away. My Dynaco A25XL and Cerwin-Vega! LS-12 speakers both produced 92 decibels when tested. 
As this chart shows, to increase the volume to make the music twice as loud which is 3 decibels louder and which is barely discernable it requires doubling the wattage output from your amplifier. So, if my 4 watts-per-channel tube amp driving the super efficient Klipsch speakers requires 1 watt to put out 90 decibels, it will require 2 watts to get to 93 decibels. To get to 96 it would require the entire amp's 4 watts. 
Knowing that, buying super efficient speakers, especially used ones, is a better way to get crisp clean sound at loud levels without having to drive an enormous power amplifier to where the lights in the house are dimming. The chart above shows loudness levels of things one might encounter. 
And finally, this chart shows the actual frequencies musical instruments produce. Note that ONLY a pipe organ can produce down to 20 hertz which is the lowest we are able to hear. See the organ pipes below? The largest (20 hertz) are on each end. Note how HUGE they are compared to the SEATS people sit in. 
Note: If you click or tap on any image, it will open in a new window over this one. At least on a PC, it does. Thus, this image of the organ built in 1871 in London England's Royal Albert Hall will open much larger.
Thank you SO much for taking the time to read this rather long article. I hope that you learned some things. Feel free to comment below or on Facebook. If you'd like to follow Anna Lapwood on Facebook: Anna Lapwood
Scott Robb
December 8, 2025
#528
