Best 845 tube out there?

I am the KR importer and have the only two new KR 845M's on the continent. My next shipment arriving in a few weeks should have four more 845M's.

While, I would love to say the KR's sound the best, they are not totally compatible with all amplifiers. This is why I insisted that KR reclassify their 845 as 845M.

At issue is the heater current requirements for the 845M. They draw dramatically less heater current than a traditional 845. Yes, they are way more efficient to heat, but the heater power is minimal when compared class A operation.

Many amplifier designers, to cut costs, do not use a regulated filament supply. When you use a KR tube, in these amplifiers, the voltage rises substantially above the rated heater voltage and the KR tubes burn up. This, unfortunately, is a misapplication and is quite visible in the tube and warranty replacement is difficult to defend.

An additional issue with the KR tubes is their plate coating, which is the most durable on the face of the planet (remember, metal plate tubes need an oxide coating). KR tubes need some run time to "sound proper," like 80 hours.

In a 10000 hour MTBF tube, this is small, but for flipping tubes, makes a judgement call difficult on short order.

If you would be interested in trying a pair of 845M's and your amp can handle it, email me at [email protected] and we will see what we can arrange.

You might consider a new suffix. There already is (was?) an 845M. I have a pair.

Szyckf I am definitely interested in trying the KR 845M's in my amplifier. I use a pair of Cary CAD-211AE monoblocks. I do not know if my amps have a regulated filament supply.

I haven't said so in this thread, but I have 3 KR 845's (not 845M's). I originally had two pairs, but one of them was burnt up by the amplifier - what had happened was that the bias capacitor to one of the 845's came adrift and snapped off, so that particular 845 socket was receiving a much higher bias current than all the other valves. I started to realize that something was up when the same socket kept on burning out 845's.

Szyckf and Amfibius, as far as I know there are no commercial 845 amplifiers that use a regulated filament supply. Not Cary, not Audio Note, nor ASL. The schematics can be found on the web.

Most DHT amps use a diode bridge > capacitor > resistor > capacitor DC supply, for two reasons:
-it costs less than a regulated supply;
-it sounds better.
AC supplies are not an option, too much hum.

Also, a regulated 10V 3.25A power supply is actually a 35-50 Watts solid state amplifier. Do we REALLY want power transistors (IC or discrete, does not matter) feeding a DHT filament, which is also the tube's signal cathode? I bet that amplifier would sound like the worst of two worlds.

So, maybe KR is feeding you marketing BS to justify a weird product?

A tube with a different heater voltage or current SHOULD get a different number. For example, there are 6SN7s and 12SN7s, self-explanatory (6 volts and 12 V heaters).
This very simple tube industry rule-of-thumb has kept users out of trouble for the last 70 years.

I wish KR and Sophia did not play those marketing games on unwary buyers.
My advice to you: do not import many of those tubes. You are bound to lose money and/or valuable customers.

I own 845 SET amplifiers and have used successfully with zero failures: Shuguang 845A, 845B, 845M and RCA 845.

I wish you good luck with your distribution deal.

To add to my "mini review" ...as in a few posts previous to this...the Kr845 has a significantly lower noise floor then the 845m or the 845b. It is extremely quiet. It sounds like a hybrid between a 300b and an 845 if you can imagine that, combining a sense of "lushness" and sound staging like that of a 300b but with the linearity of a 845. I have no reasons to want to go back to listening with a 845b or a 845m. If i am going to be serious about my music playback i have to utilize a KR845 in my system and build the system, ie cords , around it. With this tube there is no fooling around. To balance this positive review i know of a few people who do not like it. They say it is coolish. I have an inkling as to what they might be referring too but it has within its sonic envelope attributes that can't be found in the other 845 tubes that i mention and therefore deserves to be accommodated into a system via system matching. I need to make it work because its got something! My 845m and 845b are up for sale as i write this.