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In Reply to: RE: Bringing down the ripple......? posted by Tre' on July 16, 2023 at 07:27:28
When I modified the power supply for my SE amps, I tried different capacitor sizes before the inductor to maintain the voltage, but with the smallest input capacitor possible. I think I ended up at 2 uF paper in oil.
I tried different paper in oil capacitors for a cap after the inductor, but I did not like the effect (these were all very old surplus capacitors I got from an electrical supply store so that may be the reason). I ended up with Cerefine caps and I later bypassed that with a 4 uf film cap - my amps are parallel feed with the output transformer wired as an autoformer, so a different topology.
By the way, I ran far away from hum with the caps after the inductor, the Cerefine caps are 600 uF after the inductor for the output tube, and 200 uF for the input tube, which has a constant current device. Can you say overkill?
Retsel
Follow Ups:
Each of my monoblocks has one of these PS plates. That's three 680uF computer grade caps in series for the output tube (CLC). The plate contains a separate power transformer/filter for the preamp and driver stages and another transformer/filter for the bias supply. The amp is dead quiet, thanks also to an ultrasonic filament supply for the DHT output.
z
THREE 680 uF caps for each monoblock for the output tube - now I feel like a wimp.....
Back when I was doing research on DHT filament supplies, the AC supplies seemed to provide a more lively sound, but that damn hum. The ultrasonic supply filament supply might be the best option overall.
I went the DC route, with a dedicated transformer and then Shotky diodes feeding an inductor followed by a bunch of black gate caps.
One more tidbit of information. I tried different biasing methods for the input tube (6SL7 wired as SRPP), but I stopped working on this when I used a NiCad battery bias which seemed very transparent.
Your amps are very nicely laid out!
Retsel
"Back when I was doing research on DHT filament supplies, the AC supplies seemed to provide a more lively sound, but that damn hum."
I experienced the same thing, and others have too. No one seems to know what causes the higher quality sound with AC. Lots of guesses, but no real evidence. I first posted the inexpensive ultrasonic approach here on the Asylum many years ago. My prototype amplifiers went into storage shortly after that, and I just recently brought them out and finished the work.
Could you tell us more about this supply?
ray
The supplies aren't too complicated, but the writeup is somewhat lengthy. It's better if I just provide a link to where I posted the process. You might need to join in order to see the images (it's free). Here are a couple shots of my final design:
Edits: 07/19/23
Thank you. I'm redoing my GK71 amp that used these 110v modules now that I am in Australia and now have some 240 volt modules. I'll put some shielding around them.
ray
I installed the modules in the Pomona boxes primariy for safety reasons. I milled slots in the boxes for ventilation, and the boards are insulated from the boxes using .020" FR4 that I also milled to the necessary shapes. My original use of these supplies used resistors on either side of the secondary to create an artificial center tap. That was because the earlier modules had a conventional transformer at the output That couldn't be easily modified. Later modules have a toroid, and that allowed me to replace the secondary winding with one having an actual center tap. I also adjusted the turns on the primary slightly during this process to achieve the correct RMS voltage for the filament. Many of the details required to make all this work properly are mentioned in that link. It's worth reading through if you're pursuing this technique. I'll also be glad to answer any questions I can if you PM me either here or through the other site.
A minor point about the photo below has to do with the Pomona enclosure cover. These were enclosures that I bought a few years ago for a different project. They were the right size for this, so I made longer covers to provide mounting ears at both ends. One of those is shown in the earlier photo. Hammond sells cast enclosures in both styles.
Thanks for the info.
ray
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