Vielen Dank für detailierte Schaltungsbeschreibung. Tolles Video.

Thank you so much for the thorough and detailed explanation of the schematic.

Howdy. Absolutely great. I did not know and understand how the cascode works. Now I believe I do. The upper triode is actually a common grid amplifier stage. It has a low input impedance and may be designed to deliver large headroom/swing with low output impedance. Exactly what I need to drive my 2xKT88 PP. I use fairly strong anode neg. feedback to the grid around the KT88. This reduces the KT88 input impedance and increases the signal headroom demand. I use the strong neg. feedback around the KT88.s to reduce the skewing effect of the OPT magnetization. i believe not everyone understands that all transformers produce a reactive magnetization current which lags 90 degrees from the signal current. This when the signal source allows reactive currents (the power grid). End tubes cannot pass reactive currents. The magnetization current and the signal current are in sync. The only way to get the 90 degrees shift is to forward the signal voltage in time. The large gain of the cascode facilitates using strong neg. feedback around the cascode too. This will, I believe, still decrease the cascode output impedance. Much Gratitude. High Regards.

Excellent discussion and you've made sure that people like me can understand what your mods are setting out to achieve. I've done basic work on various amps, so I can at least handle a soldering iron, so this is all possible for me. Thank you! I'm running a 5U3C rectifier and 6H8C drivers. I swapped the stock 300B tubes for some TJ Music 300B/n mesh plates. The TJ's are nice, but they didn't warrant the extra expense. The stock Psvanes are pretty good.

can't wait till building starts

This is brilliant, (I had no idea how a tube amp worked before watching the video), you are a great teacher and this is a fantastic resource.

Thank you for a valuable insight. I have one of these and plan to follow your mods! You have a great understanding of tube amps!

This is one of the best substantive discussions of how tube amps work that I've seen on KZfaq! And such a fun amp to mod. Great stuff!

I'm looking forward part 2 !

Love the explanations. Some of it was over my head but it is a great learning experience.

Does this amp use AC for the 300B heater supplies or is it DC regulated? (BTW, great walkthru and comparison and of the two schematics ,you are truly democratizing high end audio vacuum tube design!!)

There's also PSRR - look at the B+, through the 10k, past the 33uF (LPF there), and then to the 6SN7, it feed B+ noise into the grid of the 300B which then comes out 180deg out of phase to the transformer, cancelling some noise. The 0.47uF cap will phase change it but you get some benefit. At least you don't have to worry about elevated heater voltages with a 6SN7, unlike the small B9A tubes (thinking 12BH7A for example).

With more than 3 times the voltage swing for the 300B grid, you should come close to getting its full output.

I was a little surprised that this circuit has no global NFB and almost if any, local NFB. I'm looking forward to seeing what the figures are.

I have a similar front end for my 300B amp, except that it uses a different dual triode (medium mu too, but higher gm type) in cascode.. I left the lower triode’s cathode R unbypassed for the cascode since my preamp is relatively high in gain..

hello and a thank you from France for your videos, could you make one on nobsound ms-10d mkii or liston rv-1800 or madison ditto? I know it's a first of the AB hybrid range but not that bad. Personally on kef 104 ab assé good but can be better with some modification, for the lamp I have already found but there may be even better than the Russian p-ev. best regards fred