23 responses Add your response
My Jadis DA-60 gets only 60 watts out of 4 KT -88s per side, in case your counting that's 15 per tube. In class A, push parallel pull pairs, if I recall correctly. They could be understating the true output in addition you can use different output tubes in this amp.
I think the output transformers playing role in shaping the sound of most tube amps.
Definitely mechans. Modjeski offers ot that he hand winds himself as a thousand dollar option in the RM-200T, but the standard ones in the non-T version of the RM-200 Mk.2 are real good, custom built for him to his specs.
Dang Normie, that's a lotta tube power! Just think---Kevin Hayes makes 450 watts with 8 tubes, yet the Atma-Sphere M-60 also uses 8 tubes to create only 60 watts. But then it doesn't have output transformers, which is even better than really good ones!
Topology and Class have a lot to do with it as well, Pentode vs Triode and Class A vs Class AB. A case in point my own amp uses a pair of El34’s per side and puts out 17 wpc, you see other El34 amps with the same output tube complement putting out anywhere from 25-40 wpc. My amp is triode wired and Class A, and runs the tubes conservatively. Pentode and Class AB with both give you more wpc, albeit with different sound characteristics.
If your KT-88 amp is only making about 35 watts, it could be because the power tubes are wired in Triode mode. This is done by tying the screen to the plate. Output power is reduced but so is distortion as the tube is a lot more linear in triode mode.
If the amp is class A and triode the output power might only be 25-30 watts.
60 watts is pretty common for a pair of KT88s operating class AB1. But its possible to get more power without going into AB2 operation although I would suspect that the VAC design with 450 watts is a class AB2 design.
Charles you are so right so many roads and they are all valid. I lucked into mine, acquiring my amp because it sounded good, not at the time really truly understanding what went into its design. Now that I know more I am still enthralled by the sound and appreciate my amp even more. And agreed on power supply and transformers both should be high quality and overspeced.
Thank you all for your input! Agreed....many roads to Rome or great sound.
I'm considering a VAC Sig 200 IQ stereo unit using a total of 4 KT88 delivering100 Wpc in class AB1 or AB2, or a Zeso Bia 120 stereo unit, also using 4 KT88, delivering 60 class A Wpc. Both are in the $12,500 to 14,000 range.
Your thoughts and preferences would again be appreciated.
Thanks Charles and jond: I will be driving KEF Ref 3 loudspeakers. My preamplifier is VAC Ren 5 and my room is very modest at 14 x 16 ft. I'm tempted to go Zesto Bia 120, albeit less power, as class A and running tubes conservatively sounds enticing. However I know VAC is synonymous with great sound. I owned a VAC Phi 70 a decade ago but that was a much different 300B beast. Both the VAC Signature 200 IQ and Zesto Bia 120 have transformer coupled balanced inputs. Thanks!
@normie57, I heard Kevin announced a VAC Ren 5 SE upgrade. If anything like my SigMKIIa SE upgrade, Jump at it now!!! Call Kevin ASAP!!! ... (Sorry, ebm took my keyboard). Improvements are staggering in all areas.
I highly recommend the VAC Sig 200 IQ. It's probably one of the most owner friendly tube amps. Auto bias, if power tube arc, IQ trips and just replace the tube. You can roll KT88, KT120 or KT150 if need more power or linear sound. For even more power, buy a 2nd run in mono. But most importantly is VAC SQ has improved, more transparency, lower noise ...
Now that's REAL creative and outside-the-box thinking! Not just a bunch of Blab Blab ... look at me, I'm the best ... hot air.
Hi all !
Class A, AB etc. But I also noticed that there are output transformerless KT88 systems. I believe its a so called cathodefollower?.
Then again comparisons with SS amps is difficult.... Tube amps are voltage related instead of SS which are current related.
Another thing.... output transformers have a specific habit. So quality of these is realy important and will take a prominent place in the pricetag..
But most important: the fun you get from your equipment!
I would still love to know how VAC gets 100 watts per pair of KT88s without tube reliability issues or distortion. Probably some proprietary secrets, the intelligent auto bias, as well as huge power supplies to comfortably generate the needed plate voltages. I have heard Kevin use The Signature 200 IQ in monoblock configuration at a couple of shows and the sound was memorable. I'll place an order and give them a spin in stereo first. I would also love to hear from Zesto amplifier owners, either the Bia 120 or Eros 300. Thanks so much!
I don’t know about Kevin Hayes and his VAC designs, but Roger Modjeski details how he gets 100 watts out of a pair of KT88’s in his Music Reference RM-200 in the company’s now-dormant AudioCircle Forum. I know MR isn’t as hip and cool as VAC, but what Modjeski has to say may still be found to be of some interest and/or value.