Audionotekit Kits Interstage 300B Monoblocks and KR 300B XLS


I recently purchased a pair of wonderful Audio Note Kits (ANK) Interstage Parallel Single Ended Monoblocks, factory built.  They arrived with Shuguang 300B's which sound quite good.  However, I have 2 pairs of unused KR 300B XLS Power tubes I bought 10 years ago. I read that they are drop in replacements for a WE style 300B but will only deliver standard 8 watts, which is fine.  I installed them in my new ANK PSE Interstage Monoblocks and they sound incredibly good.  The ONLY thing that concerns me is, at turn on, when power is first supplied to the monoblocks, there is a loud howling/moaning sound from each loudspeaker lasting 8-10 seconds then completely disappearing. (Sounds like a toilet with a bad inflow valve)  I don't think the loud howl is doing any damage to my KEF Referece 3 drivers, but I am a bit concerned as to the safety of my loudspeakers and new amplifiers.  From what I read the 300B XLS has higher filament and plate currents and plate voltage but it shouldn't stress normal 300B amplifiers, which will provide the standard 1.2 A to its filament.  Thank you for any and all advice!  Again the 300B XLS tubes sound fabulous in the ANK PSE Interstage Monoblocks after the initial inrush of power. (10 seconds or so)

audiobrian
I just read that the 1.8 A filament current of the KR 300B XLS (vs 1.2 A for normal 300B) will be drawn from the transformer supplying filament current.  Do I need to find out from Audio Note Kits whether their transformers can handle the additional current draw?....thanks again!
Reach out to the ANK guys. Your amps use D.C. Heat so you need to make sure the D.C. Regulators can handle the additional current draw. I use AC heat on my amps and EML300bXLS tubes pull the voltage down because of the extra current draw.
I wonder how significant the increased current draw of the EML XLS is. EML claims this tube is a simple and direct replacement for a standard 300b. I've used them happily for several years with no "apparent" problems. I love this tube, have I been just lucky in avoiding any problems so far?
Charles
1.2 to 1.5 amps is a 25% increase in current. That's pretty
significant. Most production amps are running D.C. So if the regulators are over spec you should have no problem. 

1.2 to 1.8 is actually 50%.

I found a passage in the Audio Note Kits manual that states that 'for 15 seconds after power on the amplifier will hum as DC current stabilizes but it should disappear completely'.  With ordinary WE style 300Bs this translates into a low level hum from the amplifier which is transmitted into the loudspeakers.  I'm guessing the 300B XLS is more powerful and apparently more sensitive to this transient DC ripple, thus the loud howl transmitted through the loudspeakers. KR website states that this tube has 4 filaments and 32 'functional cathodes'. Perhaps the construction of this tube makes it ultra sensitive for those brief 15 seconds. (and it does stop completely)

Also the Texas Instruments  LM-1084 5V DC voltage regulators in these amplifiers  are rated at up to 5A, with 300BXLS filament draw of 1.9A.  it is a parallel single ended monoblock but there is a separate voltage regulator for each tube.  I guess it sounds safe enough to go with the better sounding KR 300BXLS as long as the 15 second loud howling/DC settling noise doesn't damage my loudspeakers.


My Audio Note Kits Interstage Monoblocks do not have soft start circuitry, which according to Roger Madjeski, would prevent the brief loud noise on power up  from the EML or KR 300BXLS in my ANK amplifiers. 
Is it common for low powered SETs or even low to medium power like mine (20 wpc) to NOT have soft start power on? What are the pros and cons of soft start circuits?
Thanks to all for your helpful comments!