Stereomour II with Film Caps in PS

[Jamier]

I'm building my second S II, this time with film caps in the PS. Since the films are so much larger than electrolytics, I had to build a taller base which took much longer than I had hoped.Then I built cradles for the caps which I suspended from the chassis using all-thread and nylon standoffs. As the amp nears completion I will need to connect the caps to the terminals with leads that will be about 4.5 inches long.So, my question is, should I twist the leads of each cap before connecting to the terminal or just run them directly to the terminal ( or does it matter)? I'll try to attach photos.

[Paul Joppa]

Yes, I would recommend twisting the wires together. The objective is to minimize the loop area, so that local magnetic fields (from the power transformer mainly) do not induce hum currents. Twisting also reverses the direction of sensitivity with each turn, cancelling out much of the residual pickup.

[Jamier]

Thanks PJ,

Should I make the same number of turns per inch as the manual advises with the heater leads?

           
Jamie

[Paul Joppa]

That's a reasonable goal, but not critical.

[Jamier]

I am almost ready to voltage test the amp. I have built it in the stock configuration and included all the required tests to be certain that it functions as intended before I begin the film cap substitutions. Is it safer to replace the caps one stage at a time,beginning with the last stage and working back? I feel like this approach will have greatest chance of success. I am concerned that if I change all the caps at once there could issues at the end of the PS that might be a problem, like increased B+  Voltage. Given that the film caps should have lower ESR, is this a possibility? If so I guess I will need to increase the values of the 130 ohm resistors that seperate the caps(?).

Jamie

[adeep42]

Some of you guys really blow my mind. Your Skills are just off the charts. That's just beautiful!!!!!!!!!!

Alan

[corndog71]

I've used Clarity Cap TC film caps in several projects from my Bottlehead Reduction to my VTA ST120 and they do a great job.  I don't believe you need to change resistors.  Another great feature is they discharge within a few minutes of turning off.

[mcandmar]

Fancy mounting brackets, how did you make them?

[Jamier]

Hi Mark. This is the reason I haven't finished my F4. I'll be getting back to you for some more advice when I pick that up again. The cradles for the caps are made from 3/4 inch pine. I started by routing holes that are the same as the diameter of the caps. Then I cut those in half creating the cradles. Those half pieces are then placed back to back with about 1 inch of space between them and screwed down to a piece of 1/8 inch aluminum that has holes in it to allow zip ties to pass through it to hold the  individual caps. Some end pieces of the same 3/4 inch pine completes the cradle.They hang from the chassis on All-Thread, washers and nuts. I sprayed them with rubber paint (Plastidip). It's all gotten from Home Depot (well, actually Lowes).MDF might work but the end pieces are screwed to cradles and screws just don't hold well in MDF.

[mcandmar]

Nicely done, looking forward to seeing it finished

The F4 isn't as much fun to build, but its a wonderful pairing with a tube preamp.  You get the best of both worlds without the compromises.

[JamieMcC]

Super effort I bet its going to sound just epic.

[Jamier]

Thanks to Alan, Rob, Mark and Jamie for the words of encouragement. I really hope this works out. If it does I will post all the construction details so anyone can duplicate and/or improve it.

Jamie

[Jamier]

And, to PJ, for the words of wisdom.

Jamie

[BNAL]

That is some great work. I wish I had good woodworking skills like that.

[Jamier]

I finished the stock build, resistance checked, voltage checked and now listening to the stock configuration. I will let this run for a 10-20 hrs to be sure there are no problems and then I will replace the last stage ( the last 100 uF caps) with Mundorf 100uF M tube caps. If that goes well I will change the second stage, listen for a while and then move on to the 220uF caps in the first stage. The second stage will also be the Mundorfs, the first stage will be replaced with Cornell-Dubilier 947C series 230uF / 1KV caps. I chose these particular capacitors for a few reasons. They meet the required specs, have good reputations and, while physically large, still fit under the new base that I built for the amp with enough clearance to remain well below the warmer components of the amp. I created adequate ventillation in the base (I hope) and suspended the new caps below this level feeling that air will enter above the caps to keep the rest of the components cool, carrying the heat out the top leaving the area around the new caps relatively cool. The replacement film caps also have screw terminals which made this process much easier with all the in and out that comes with fitting, etc. Originally the plan was to use ASC PP in oil but I could only find 50 uFs which required 8 of them. I tried several configurations but I just couldn't get them under this base with enough room to spare so I had to go with Mundorfs. So as this process moves forward I will compare each change to the stock SII that I built a few months ago and make progress reports.

Jamie