That's quite some work you've put into this. Thank you!
I've already downloaded the expressSCH, but your file makes it a lot easier.
Ok
1) I love switches, but I chose the dual input switching system for a cleaner faceplate look. The dual inputs, are simply utilized by the switchcraft marshall-type jacks. The 2 pins make connection when nothing is inserted, and can thusly be used as a passage for signal. I've included a picture "jack wiring" to show you the signal ways. Red is single triode (pale red being the grounding passage when using parallel triode), and blue being Parallel triode signal way.
2) The NFB resistor 22K is stationed at the output 8 ohm jack for wiring convenience, and the 5K presence knob being the other end of the voltage divider (remember to disable the jack switch if doing it this way, otherwise the 22k resistor is bypassed when nothing is inserted into the 8-ohm jack). This is taken directly from Sluckeys November schematics, where he mentioned that 22K gave a better response than 100k. I do not recommend ditching the presence-knob in favor of a switch, the presence knob seems very much needed in this design. Although a switch to completely deactivate the NFB loop could be of use.
3) I chose the EZ81 rectifier simply because Tube-Town had already predrilled a lot of the holes, and i felt no need to use a different rectifier. Although the TT transformer has a 5V heater tap to do so. Also there is a relatively small voltage drop across the EZ81, which was a plus in my book, according to my friends wishes of a very fast response with a tube feel. Whether you will even notice "sag" at any level is still something I question. Nevertheless it's fairly cheap to incorporate and I chose to do so for "cool factor". The solid state / rectifier switch is taken from another thread on the forum, the only difference is that I chose to put an "always in circuit"-47+47uF filtering on the solid state line, to get the heavy filtering seen on D-style amps, while still keeping it fairly low-filtered on the EZ81 line. I'll try to draw it in the coming schematics.
4) The cathode/fixed bias circuit is a direct rip-off from sluckeys november build, and it works like a charm. Only thing I did was to use the Mark Huss plexi6v6 bias circuit, although I changed the 220k resistor to 150k and the bias pot to 25k-L to accomodate for the lower voltage secondaries transformer. I'm a big fan of cathode biasing myself, why chose to incooporate the switch since the original designs use fixed biasing. I can see you made the cathode bias resistor 270R, I think this is too small for 6V6s. The voltage across the cathode resistor is nearly 27V, and thus 400R puts it at 95% of max plate dissipation.
Also I do not recommend any bypass capacitors after V1. I originally had a 5uF bypass cap on V2a, but this stiffens up the feel of the already quite stiff amp, and overdrives V2b nearly at any volumes. Using the split plate resistor in "slow" setting and no bypass cap on v2a, and a 100k resistor to ground just before v2b, ensures that v2a and b clips around the same time, giving a much warmer and rounder break up. If you were to overdrive the preamp section, I strongly recommend the use of plate-to-cathode capacitors of 280-390p as seen on the D-style overdrive section. This keeps the overdrive from becoming overly harsh, although it will take a way some shine when playing clean. Something i did not like. Bear in mind that you can surely overdrive this amp. My LP with medium-high output overdrives the preamp around noon when using HI input, and "fast mode". The preamp is overdriven when fully cranked with a strat. I prefer a slight overdrive on the preamp and having the power amp overdrive the rest, when not designing the amp for strictly rock-and-roll purposes. But to each their own :)
Hope this cleared up some.
Kind regards
Christian
Topic: Dumble 20 Watt 6V6 Build - with pwetty pictures! (Read 17177 times)