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Old 25th September 2008, 08:36 PM   #1
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Default F3 Power Transformer

I've been looking around for a cost effective transformer for an F3 build and am wondering if this is adequate:

http://www.partsexpress.com/pe/showd...number=122-620

It's dual 18v secondaries, but 250va... maybe 2 of these for dual mono supplies, or could I get by with one of these to get started with?

I have searched the site for this info, but F3 is only two letters long, seems the search engine needs three letters minimum

Thanks,
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Old 25th September 2008, 08:55 PM   #2
cfcubed is offline cfcubed  United States
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Yes, it took a bit of digging around here to pin down transformer requirements for my mini-Aleph & F1/F2 builds...

I used AnTeks like this one and they are working fine for me. There are better toroidals around (for more $$s), but mine are nicely serving their purposes for me (no hum mechanical or otherwise, don't get overly warm in my builds, etc.).

Good luck!
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Old 2nd October 2008, 11:01 AM   #3
gionag is offline gionag  Italy
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don't exagerate with VAs....

IMHO is still sufficient a 350VAC for both channels.

In my model i used a 650VA (for both ch.) and i have a lot of problems with start-up and 8 amps per rail is a huge value...
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Old 2nd October 2008, 03:33 PM   #4
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TVMan,

In the US, you can also use the 240vac primaries with 120vac to halve the secondary value.

This model might also work "Avel Y236752 330VA 35V+35V", if you need a higher VA rating. With this model, you'd need to wire it up as a 220vac for 120vac to get 17.5vac out.

http://www.partsexpress.com/pe/showd...number=122-650

Looking at tranfo's with double the voltage output and then wiring them up for 220 provides more options.

-David
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Old 9th October 2008, 05:08 PM   #5
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TV man,

Search for "F3 Amp"

A 250VA trannie will do the job quite well - no problem. Just hitch up the two secondaries to give 36V for both channels, and feed them to seperate diode bridges for L& R supplies. A bigger trannie will be better, but as you say, try one first and see - at <$50, good price.

The F3 draws about 1.6A at 48V (dc) per channel (about 80 VA).

As David has said, the 330VA one is probably better and the 35v instead of 18+18v won't be a problem either,

The recommendede use of the CL60 on each of the Act & Neut supply (110v - USA) will stop all the surge problems - however, they DO alter ther sound a bit, so use them as the current limiting "resistors" on a standard soft-start cct.

While talking about the transformer, strongly suggest use of seperate diodes (u/fast ones, too) instead of the commonly used block bridges - makes HUGE difference to sound.

And for heavens sake, don't use cheap wiring for it - spend a few bucks and get some instrument wire, speaker wire, etc, of at least 1 sq mm conductor. (#18 ?)

Incredible amp with good supply and Simics - better yet with BG-NX caps. Try it with headphones!!
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Old 11th October 2008, 05:22 AM   #6
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Thanks for all your replies

Was digging around the closet today and found two nice old transformers from a non working Kenwood 6300 (?) integrated amp i disassembled a few years ago. The 6300 was rated for 80-100w in class AB. The transformers could be used in dual mono, but i wonder if they pass enough current. They're pretty heavy, but don't have any markings indicating VA rating. I'd like to give them a shot, but wonder if they'll over heat...
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Old 11th October 2008, 05:24 AM   #7
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Wondering too how much heatsinking the Lovoltech power JFET needs.
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Old 11th October 2008, 05:40 AM   #8
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Forgot to mention the transformers are 36v, perfect for the F3 if they can pass enough current.
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Old 11th October 2008, 05:41 AM   #9
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Measure it! Don't guess.
Suggest buy one with known parameters and don't just knock up a doghouse.

The Lu (with 1.6A) dissipates about 6 Watts. Do read the ZV9 and F3 articles. Need to track with o/p devices (temp).
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