Finally the Captain 845 PP amp is presented to you
It has been a while since I have done anything about 845 amp design, the Outerlimit has been built and is very satisfying it is not very encouraging to know that better will be very tough.
But maybe as good at a fraction of the price and more power is a viable and valid target. Also Lundahl has new output transformers with Amourphous cores and I also ordered Amourphous cores for LL1660 interstage transformer because Amourphous cores have big advantages in Push Pull designs. For Single Ended i would say they are sounding worse.
2 versions exist of this amp, 6BL7 as driver and the KT 66 as driver. The former sold as kit and the last one sold as kit and build. Thats because with the 6BL7 a stereo integrated was also possible as previously build.
Schematic brief description :
Long tail phase splitter with current sources in cathode, drives the PP min output stage so the 845 can effectively be driven into saturation.
Signal cabling is point to point, Mundorf silverfoil capacitors in signal and electrolytic with mkp mpp in powersupply.
No feedback and top notch components where needed also some chokes used in powersupply where necessary.
As usual negative bias is foreseen and this with the necessary regulators , also a nice delay for the high voltage is done for the commercial version .
Powersupply are a bit different offcourse depending on which version you want to build, but both are offcourse overdesigned and will satisfy totally. this amp really has extreme power and super tight control over the entire frequency range its just amazing the scale of downward dynamics that suddenly an amp can achieve . Also it makes u feel what power in a velvet glove sounds like . Not to warm sounding but never the less tube sound and excellent precision with very good tonal balance. The bass is exceptional, i dont think transistor does any better .Another proof that tube amps can outperform any transistor even in the bass department .
Amp was presented at a few high end shows and was positively received.
Picture of a small audio fair in Paris 2005.
A few pictures of the beautifull inside of this amp
Top under the hood
Schematics 6BL7 version
As can be seen, finally a balanced input is available. Since physically this would have been very heavy it was opted to build monoblocks.
Simple straightforward design, long tail phase inverter using the excellent 6SL7 tube, military version is 6188. A pair of KT66 in push pull drives the interstage transformer.The reason why i opted for KT66 is that it is the 2A3 of the tethrodes and is better then the KT88 and others.Quad new what they where doing when they selected the KT66 for their famous Quad II .The 845 use AC filament current because in a PP design the hum cancels and therefore this is acceptable. The LL1620AM PP is the ideal output transformer for a 211 or 845 output stage. Neg bias is applied to all power tubes as it is sounding faster and more precise then autobias.
and the power
Expected output power
Class A 70Watts RMS
Class AB2 125Watts RMS
Class B 200Watts RMS ( i would be surprised if anyone would ask for this to be biased in class B )
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