micpre#9

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ioaudio

Well-known member
Joined
May 11, 2005
Messages
2,087
Location
vienna/austria
again a pentode/double triode circuit, but this time i changed the output stage and ommited any kind of feedback completely.
its not build yet, what do you think?

micpre%239%7E0.jpg


edit: output transformer ratio.
 
[quote author="solder_city"]pentodes w-out feedback are great if u like noise and distortion.[/quote]

yes, i´m completely addicted to noise and distortion :twisted:
seriousely i dont care for 3db more noise, as long as its nice audiophile noise :green:
can you suggest good reading about partition noise and such?

what about the output stage around the ecc88, do you think it works nice?
 
what tube is the ecc 88 output?
the cathode resistor looks low, i know you have two sections = 1/2 cathode r value, but it still looks a bit low.
how much current thru output plates?

you need the grid biased up for headroom due to strong hits on the ef 86.
 
[quote author="CJ"]what tube is the ecc 88 output?[/quote]

while i can't speak for io, i think he's using a ... ECC88 :wink:

[quote author="CJ"]the cathode resistor looks low, i know you have two sections = 1/2 cathode r value, but it still looks a bit low.
how much current thru output plates?

you need the grid biased up for headroom due to strong hits on the ef 86.[/quote]

depends on the B+. if it's 250VDC, and he's dropping 100V across the 10k, 10mA is flowing through both tubes, which gives a bias point of roughly -3V and a a (single) cathode resistor of 300r

i'm not sure this is the best operating point. you need to push a lot of voltage through that ECC88 with a 10:1 output tx

not too fond of the EF86s (or pentodes in general) and i probably would have used a pair dual low MU triodes instead
 
[quote author="sismofyt"] you need to push a lot of voltage through that ECC88 with a 10:1 output tx[/quote]

uhh, thanks for pointing to that...the output transformer should be a 4:1 10k:600 , i mixed that up on the schematic!

i think cj was asking for the type of ecc88, in regards of its capability to push current maybe? but i dont know yet, just planning...



[/i]
 
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