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)
- Here's the schematic of how Magnavox used to do it. - wpod 17:55:24 03/16/07 (2)
- Re: Here's the schematic of how Magnavox used to do it. - Eli Duttman 18:29:34 03/16/07 (1)
- Another option - Owen 06:46:37 03/19/07 (0)
- Re: single ended EL84 in pentode mode - AnalogSushi 13:39:20 03/16/07 (3)
- Re: single ended EL84 in pentode mode - Eli Duttman 16:31:03 03/16/07 (2)
- Re: single ended EL84 in pentode mode - AnalogSushi 18:12:22 03/16/07 (1)
- Re: single ended EL84 in pentode mode - AnalogSushi 06:27:46 03/17/07 (0)
- Re: single ended EL84 in pentode mode - andrewbee 10:01:51 03/16/07 (1)
- Re: single ended EL84 in pentode mode - eedork 12:04:39 03/16/07 (0)
- Re: single ended EL84 in pentode mode - Eli Duttman 15:52:37 03/15/07 (8)
- thank you - eedork 18:09:44 03/15/07 (7)
- leave the tube rect in & add ss at the same time - Janos 16:10:09 03/18/07 (0)
- Re: thank you - Eli Duttman 18:53:02 03/15/07 (4)
- Re: thank you - eedork 04:11:41 03/16/07 (3)
- Re: thank you - Eli Duttman 16:41:18 03/16/07 (1)
- Re: thank you - eedork 18:49:31 03/16/07 (0)
- Re: thank you - eedork 04:38:44 03/16/07 (0)
- Re: thank you - zobsky 18:20:58 03/15/07 (0)
- Re: single ended EL84 in pentode mode - Tom Bavis 14:24:24 03/15/07 (0)
- suggestion: be sure to clamp down on the screen voltage (NT) - zobsky 11:02:30 03/15/07 (2)
- Re: suggestion: be sure to clamp down on the screen voltage (NT) - eedork 14:12:15 03/15/07 (1)
- Re: suggestion: be sure to clamp down on the screen voltage (NT) - zobsky 15:26:52 03/15/07 (0)