100v or 63v capasitors for the Aleph??? - Page 2 - diyAudio
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Old 1st February 2006, 11:13 PM   #11
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All the models in the range are wonderful but I took a shine to the one second from the left.

..I don't think I am alone on that score!
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Old 2nd February 2006, 08:38 PM   #12
folkeb is offline folkeb  Norway
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I have a possible solution given to me elsewhere. If I go for transformers with secondarys at typically 45v, this would give some 63v out. If I then use resistors with high watt tolerance then I could adjust the voltage to about 58. With this it should be safe to go with the 63v. Is this a correct, or to some extent correct to asume? If so, I'll put in 8x47000uF for each channel, brand: Fischer and Tauche as these have been recommended in this forum (better values than the RIFA)
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Old 2nd February 2006, 08:54 PM   #13
MikeW is offline MikeW  United States
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You will not get 1.4 X VAC in a class-a amp. It is more like 1.2 to 1.3 depending on your current draw?
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Old 2nd February 2006, 09:09 PM   #14
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If you have around 60 volts and use 63 V caps I see no problems with it, what so ever.

I have had 47 volts on 40 V caps since 1977, works still. Seimens caps. Almost 20% over voltage is maybe a bit much but in your is totally safe.
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Old 2nd February 2006, 09:19 PM   #15
MikeW is offline MikeW  United States
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Quote:
Originally posted by peranders
If you have around 60 volts and use 63 V caps I see no problems with it, what so ever.

I have had 47 volts on 40 V caps since 1977, works still. Seimens caps. Almost 20% over voltage is maybe a bit much but in your is totally safe.

Not always a good thing P-A.
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Old 2nd February 2006, 09:33 PM   #16
folkeb is offline folkeb  Norway
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I'm sort of confused. The dealer first recommended that I should go for 50v on the secondaries, however not with 63v capasitors as he said this would be a safety issue. Also he says that "his" transformers give 1.4 x VAC. So he recommended 45v and then use resistors to bring the voltage down. As it is, I don't know anything about transistors and class A. My problem is that I would like to get within a safe operating voltage range (for 63v capasitors), but at the same time stay as close to the 60v(rails) of the original (and 200w) Aleph 1.2. Can someone explain me the details or give me a reference to a thread with more info?

I plan to use CLC (2x47mF, 2.2mH 0.1ohm, 2x47mF) if this is of any help.

Are the big differences within transformers with regard to actual secondary voltage, as in; do different transformers with the same spesifications give the same secondary in the same setup?

Thanks for your help and insight!
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Old 3rd February 2006, 09:49 AM   #17
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A 50 Vac transformer gives 70.7 Vdc, 50 *sqrt2.
A rectifying diode causes a 0.6 volts drop, after rectifying you get 70 Vdc.
The voltage coming to your home can fluctuate, probably 10% higher as it can be here.
So the actual transformer voltage can be 77 volts.
Without a current load the voltage can become even higher than that, depending on the type and size of the transformer.
Average values are 5%, so for 50Vac transformers the secondary can become as high as 80 Vdc.

That is without a load. A regular amplifier is Class AB, without a signal the current through the output transistors is very low.
So low that the voltage on the capacitors may reach 80 volts, for such an amplifier you need capacitors that are rated for 80 volts minimum.

A Class A amplifier has high bias currents going through the output devices constantly. On an Aleph amplifier these currents start running the moment the voltage level is high enough to open the output devices.
With this constant load the regulation factor of the transformer is of no importance. (the 5%)
Transformers that are loaded do not deliver the nominal voltage, the voltage will drop from the 50Vac to a level that again depends on the size and type of transformer.
But even the highest load will not bring the maximum output voltage of a nominal 50Vac transformer below 63 volts, you need to use a lower voltage transformer on 63V capacitors.

The next regular series lower voltage transformer is 45Vac, loaded it will get near 60 volts dc. How well depends on the transformer you intend to use.

I tried F/T capacitors a long time ago, they were easy to buy here, not impressed by them then. I gathered the high voltage double capacitor F/Ts are good for tube amplifiers, no idea how well the current production lower voltage F/T capacitors are.
A 33.000/63V Fischer & Tausche does $30 here, i bought the PEH169 for a lot less.
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Old 3rd February 2006, 10:12 AM   #18
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Hi, volkeb

I would try 4 (or 6) X 47,000uF/100V instead of 8 x 47,000uF/63V, reminding me of the original having 4 x 25,000uF . . .

Good luck.

Regards
jh
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Old 3rd February 2006, 10:26 AM   #19
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Quote:
Originally posted by folkeb
My problem is that I would like to get within a safe operating voltage range (for 63v capasitors)
A 63 V cap will start to leak around 70 V approx. So can you garantee not more than 65-67 V it's perfectly OK.

Which transformer are you going to use, VA rating and secondary voltage?
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Old 3rd February 2006, 12:26 PM   #20
folkeb is offline folkeb  Norway
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I'm thinking of two 625 VA transformers, for a total of 1250 VA with two 45v secondaries. I know that many in this forum use a lot bigger transformers, but the original (as far as I can see uses 1200 VA). Another issue with higher voltage is the increased power, and size of heatsinks.

My conclusion is that 63v capasitors will be fine with 45v secondaries, and that this voltage will after the brigde recifier and so on give something in the region of 60v on the rails, give and take some. On PassDIY 42v gave 57v, and the capasitors where in this project 63v.

If I had a good deal on the PEH169, all would be well. However, I have not and ca. 25 euros for F&T 47000uF is not too bad from what I have experienced (actually quite good in fact).

F&T were hyped in a dutch thread. If I'm not mistaken they were the same as Krummer or Mundorf to much higher prices. I'm not sure, so don't take my word for it. Unfortunately, I can't find the thread again.

Thanks for all the respons! This is a great forum!
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