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Re: Me too, what power tranny?


 
12/15/1999 7:42 PM
Benjamin Fargen
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Re: Me too, what power tranny?
Damn Bob!!!!!  
 
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???????  
 
Thanks,  
Benjamin  
 
 
12/15/1999 10:40 PM
Bob A DynaQamps
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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.  
 
Playing safe;  
 
Bob @ DynaQamps
 
 
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12/15/1999 11:26 PM
Benjamin Fargen
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Bob,  
 
Smart thinking.........  
And your right, it never hurts to have some headroom to play with!  
 
Thanks for the input!  
Benjamin  
 
12/16/1999 1:47 AM
Lee
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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
dave rutherford
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I have the 270FX in a 2-el84/2-12ax7 amp and get 350v b+ (5ar4 rect.) FYI.
 
12/16/1999 5:50 PM
Benjamin Fargen
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Dave,  
 
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.  
 
Benjamin
 
12/16/1999 6:15 PM
Max
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Re:anyone has built a spitfire?
Hi guys!  
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.  
Best regards.  
And thanks for your help.  
Max.  
:@)
 
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