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single ended EL84 in pentode mode

All,

I'm new to this forum. I've posted numerous times on the Bottlehead forum in the past, but am just now getting back into the hobby after a 4 year break.

I'm interested in building a small EL84-based amp using iron that I I salvaged from an old console. I measured the OPTs to have a 4.5k primary and am thinking of building this circuit:

http://db.audioasylum.com/cgi/m.mpl?forum=tubediy&n=9930&highlight=SE+pentode+EL84&r=&session=

I need to figure out if my 4.5k OPTs will work also. Based on a quick scan of the data sheets for an EL84, 4.5k should be fine for a class A1 amplifier using a plate voltage of ~250V.

I like the idea of SE pentode since I'm fairly certain that's what the original console amp was (it had an EZ81, 12AX7, and 2 EL84s). I've never designed or built an amp using feedback, and the whole concept is very foreign (and baffling) to me at this point. I have many questions about negative feedback - how much do you apply, how do you design for it, etc. I'm hoping that I will learn more about it as a result of this project.

It seems that I'm in the same boat as the original designer (Erik) who posted this schematic!

Does anyone have experience with this circuit?

I've also come across this second schematic which looks interesting as well (some of the values are incorrect, as noted in the post):

http://www.diytube.com/phpBB2/viewtopic.php?p=1261&sid=6693fd10a1e28cb49ee75552b709a6a7

I know this topic has been discussed many times (I've searched and read many posts over the past few days) but I would appreciate feedback (no pun intended) before I begin.

Thanks!
-Matt


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Topic - single ended EL84 in pentode mode - eedork 10:28:50 03/15/07 (22)


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