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Old 8th November 2006, 06:46 PM   #1
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Default best type cap for preamp PSU

Yet another Aikido question (I apologise)

My PSU has been designed, and I have bought some surplus/used motor-run caps 1.5uF, 45uF, and 60uF.

Now, the thing is - the 45uF is huge (2.5 x 5 inches), and the 60uF is not much smaller. The 1.5uF is small enough to not be a concern.

I looked in the Antique Electronic Supply catalog, and they supply CE can capacitors that are made using Mallory specs and equipment. These are FP type cans and a multisection 30/40/80uF 525VDC measures only 1 3/8 by 3.

Capacitor size is going to have an effect on the size chassis that I eventually choose.

So, how would this FP cap sound compared with the 45uF and 60uF motor runs caps in the PSU? I would still use the 1.5uF AC motor-run for the cap-input to the first choke.

Thanks,
Charlie
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Old 9th November 2006, 12:16 AM   #2
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Use the motor runs from small to big with a couple of chokes in between and get a big chassis. I used some Mallory computer grade electrolytics once and whatever they did for computors they were complete **** in a tube PSU. Dead, slow, sluggish, dreadful.
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Old 9th November 2006, 03:03 PM   #3
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Eusebius,

Well......I'll be using the motor runs caps then!

Where in Britain are you located? I grew-up in Rochdale.

Regards,
Charlie
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Old 9th November 2006, 08:23 PM   #4
Bengali is offline Bengali  United States
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Hi Charlie,

I'm starting on an aikido board. Did you finish building yours?

Did you make a preamp or amp? If you don't mind me asking what tubes did you decide on? Did you go with SS or tube rectifier?

I'm still looking for a 5ar4 tube power supply circuit. My transformer will be 234V. I think the 5ar4 drops 17volts, so I'm left with 217v. I just need 200V for the +B, 6cg7/6dj8's.

I don't know for preamp, if the +B should be regulated or non regulated.

thx.
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Old 10th November 2006, 02:51 PM   #5
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Bengali,

I just stuffed and soldered the Octal Stereo preamp board. It was really easy work. I will use four 6sn7's as I want to keep to gain relatively low.

My hunch right now is to build the PSU in a separate case to the preamp. I'll sit the PSU on the floor and run umbilicals to the preamp.

The PSU consists of Hammond 269AX (125-0-125), a bridge rectified using 1N4007's; 1.5uF cap, 10H, 155 ohm choke; 45uF cap; 10H, 155 ohm choke; 60uF cap. That will give around 300VDC. I will use a separate transformer for the 6.3VAC heaters.

What this will mean is that I can keep the noisy components away from the actual preamp.

From what I have read, the arrangement of the tubes in the Aikido really minimize on noise. I am not planning on regulating the B+.

Good luck with your Aikido.

Charlie
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