Tube Amps / Music Electronics
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|12/15/1999 7:42 PM|
||Re: Me too, what power tranny?|
What kind of idle current are you running across those EL84's? My "Epic" amp is running about 42 ma per tube with a plate voltage of about 310VDC.
You figure thats only 84 ma + 1.5 ma for each 12AX7.......how are you pulling so much current?
You must be running those EL84's way above max dissapation rating???????
|12/15/1999 10:40 PM|
|Bob A DynaQamps
Benjamin, I'm running the tubes at about 40 ma. each. Your figures are about right for idle current. The issue that I don't here about is the current draw while in use and under high demand. English amps usually have larger transformers than Fender's and seem to run cooler. I've tried a Thordason 120ma. trans on that design and it gets pretty hot. When it'the "cranked up mode" this amp was drawing 148 ma. I'm not comfortable with this design without a least a little head room. Say, 160-180ma.
My plate voltage is about 350vdc with current @ 37 ma. Idle current is around 90 ma. But when you gas it, it draws up to 150 ma. Now I don't know about you but I like to play my amp big and bad so you need a larger trans.
Bob @ DynaQamps
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|12/15/1999 11:26 PM|
And your right, it never hurts to have some headroom to play with!
Thanks for the input!
|12/16/1999 1:47 AM|
OK, the FX it is. I'll use the output tranny that is in the amp now (2xEL84). I need a different power tranny because this old Traynor is pulling 438v. B+ from its 330-0-330 unit and s.s. rectifier. I haven't played it much but I don't imagine the power tubes would last real long at that voltage.
|12/16/1999 5:20 AM|
I have the 270FX in a 2-el84/2-12ax7 amp and get 350v b+ (5ar4 rect.) FYI.
|12/16/1999 5:50 PM|
Good info........as Doc has pointed out in the past, hammond transformers are rated for a 115 AC supply. So your really seeing about 280-85vac off the secondary instead of it's 275 rating.... depending on you AC outlet. We all know after you throw in the rectification calcultaion ( x 1.414) your dealing with quite a bit higher B+ than any original (Smaller) Vox ever had.
I used the old zener trick ( thanks again Bruce) to drop it down to about 305-310vdc. This gives you a little bit more
relief for today cheap ass tubes.
|12/16/1999 6:15 PM|
||Re:anyone has built a spitfire?|
I set my mind on the spit.
But there's somethings i want to ask.
1,does Hamond makes a 272 in 220V?
2the two grid two res,are 100 but what?100 omhs i guess?
3same thing with the 120/5 watts omhs again?
4The first 12 ax 7 looks like the two triodes are connected in paralel(look at the pin numbers on Ampage schem)
5what are the specs for the choke.
6Where do i find cheap caps in europe?
or can i replace the three after the choke for 330 Mfd 385V
I know the first one i can't,it would make too much of a curent draw onto the rec.
And thanks for your help.
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