Tested the 45 filament circuit based on the capacitance multiplier. Initially got the wiring of the MJE3055 wrong, but rectified that mistake. Strange that at the LT1083 output, voltage is 2.45v, but at 45 filament, it is 2.28v. It's just a wire in between... Odd.
This perf board is for one stereo channel only. Need to build one more for the other channel when a working prototype of the amp is achieved.
Tested the capacitor multiplier and it seems to work! I used some nice parts here for the filament dc circuit. Shindengen 4A Schotty bridge diodes for rectification, followed by some Nichion Fine Gold capacitors that's reused from my very first diy project. The current regulator is a LT1083.
Need to get a few more of those larger heatsinks for my LT1083. The voltage output at the tube is around 1.65v. A little higher than the supposed 1.5v. Should not be an issue.
The same perf board will hold both the circuits for the 26 and 45 tubes. Was doing up the portion for the 45 last night.The circuit can be found at Rod Elliot's ESP site. I used two MJE3055.
There goes thoughts of re-using the power transformers. B+ after regulation has to be around 455v. I probably need around 500v prior to regulation. This also means the capacitors would need to be put it series or to use the huge oil types. Unfortunately, I only have three 660vac oil run capacitors. The rest are 370vac types.
Now, I'm starting to wonder if the C4S can drop that much voltage. Is it able to handle the wattage?
VoltSecond has some useful information about implement the C4S at his site. Just reading off the chart, it is best to keep the C4S under 300v across the MJE350. One easy way is to drop the voltage with a resistor prior to the C4S. At 5.5mA, I would need a resistor of 30k ohms to drop the voltage to 290v at the top of the C4S. This will result in a R2 at the C4S of 145k ohm.
So, here's the scribble on paper. Operating points are pretty standard stuff for 26 and 45. The brief is simple... DC coupled amp, with driver C4S loaded and with LED biasing. Filaments will be DC current regulated. B+ will be regulated by a HV Maida circuit. Tamura F475 is intended to be the output iron, but I may A/B the FT10S that I got from Andix.
Chassis will be a departure from the tower types that I have been building. I'm veering more to the Fi designed ones. Wanted my wife to lug any fi stuff back when she was in New York some time back, but boy, there's a long back log being fulfilled by Don Garber.
Anyways, since the 6T10 project was not successful, I should look for another project that can hopefully reuse the power transformer. The 45 fits the bill as I've already got suitable output transformers and even a pair of RCA 45 tubes. I've also got a stash of 26 driver tubes. This will be my first all DHT amp. Wonder what challenges I will face... Should prototype this on a board first... ;)
Work on this hopefully will start at the end of this month.
ps. an eagle-eyed reader highlighted that my schematic has some mistakes around the cathode resistor for the 45 tube. i've forgotten to stack the driver voltage for the DC arrangement. will update the schematic tonight. thanks nick!
