a bit OT: so ive decided to build a firefly...

[jimmy]

hi everyone

after much debate ive decided to build a firefly. its my first high voltage project. ive studied the schematic and ive got a few questions:

1) it says to use 400V caps. problem is i can only get a few values in 400+ volts. the schem for the AX84 project has 25V caps in places. where can i use lower voltage caps in the firefly?

2) 240V comes out of the wall in Oz so getting a 1:1 transformer from jaycar is a little odd. can i use this one? they jaycar cat number is MA1512. sorry the url is huge. its an isolation transformer but it says something about telephone lines  :?

cheers
Jim

[Paul Perry (Frostwave)]

The MA1512 transformer from Jaycar shouldn't go anywhere near the mains!! It is for isolating phone line stuff from ground,  it won't work as a mains transformer. Where is the Firefly ckt?

[Peter Snowberg]

I think you'll like the results:

The only positions that you could use 25V caps in would be C2, C3, and C6. Even there I would still use 50 volt units, or 35V at the very least. Maybe that's overkill; a voltmeter across them will tell. I think it really helps to use good quality caps for these positions too.

As Paul mentioned, a 1:1 telephone tyransformer will not do any good unless you want fireworks. You need a real-deal 1:1 line isolation transformer made for plugging into 240VAC. You can also use two filament transformers. The first one takes 240 to 6.3 or 12.6 for the filament and the second one is wired in reverse to step the low voltage back up to 240V. You could always use a 12VAC wall transformer to power the amp and put the step-up transformer inside teh chassis. Then if you travel with the amp, all you need is a new 12VAC wall adapter.

-Peter

[petemoore]

From the clips I heard, I'm certain I would like a Firefly amp.
 Your homebrew ckt's will be 'happier' seeing their ouputs coupled to tube technology...IMO...TUBES RULE [for powering guitars/efkts into speakers].

[jimmy]

thanks for the advice!! soooo i can use 2 of these 12.6V transformers instead of the two in the schem? they are 500mA. is that enough?

built my chassis today in electronics class. thank god for my teacher!! he supplied me with all the materials needed. good bloke. its 30cm by 20cm by 5cm. i capitally stuffed one side because the block i was drilling in to moved and the drill bit went in diagonally and made the holes too big for the rivets :x  so that panel is the back.

if i have any probs ill report back here.

cheers
Jim

[Peter Snowberg]

Two 500mA transformers will give you plenty of power to spare for both low and high voltage.

I hope you can post pictures.

You're going to love it!

[jimmy]

awesome!!! all i need to get now its tubes and that output transformer...

the wheels are in motion...

cheers
Jim

[Ansil]

i may be a little late on the thread here. but i thought i would trhough in my two cents here.   you can also use center tapped transformers and connect the 12.6 volt side of one to the center tap and to one side of the coil, to get more voltage, as long as you have a good transformer it should be fine.  i have done this a few times.  of course the first one i built had three transformers..  one 120:12.6v  centertapped. to give me the 6.3v to the tube heaters.  then it went into one centertapped 12.6:120v and also at the same time went into a standard 12.6v:120v transformer, to give me like 140V for the preamp and around 200 something volts for the power section.

[jimmy]

yeah thats what ive done in my setup.

cheers
Jim