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Old 28th August 2009, 04:28 PM   #1
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Default looking for fairly simple project for Eico 81 OPT's

Hi,
I recently picked up a pair of nice OPT's from an Eico 81 amp. I am looking for a good, fairly simple to build, EL84 or similar PP schematic to use them with. I have Googled and searched around some but haven't really seen anything that caught my attention.

Thanks for your help.
Jeff
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Old 28th August 2009, 06:00 PM   #2
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Quote:
Originally Posted by jmillerdoc View Post
Hi,
I recently picked up a pair of nice OPT's from an Eico 81 amp. I am looking for a good, fairly simple to build, EL84 or similar PP schematic to use them with. I have Googled and searched around some but haven't really seen anything that caught my attention.

Thanks for your help.
Jeff
The Dyna ST-35 is one - and you can by a PCB at diytube.com. Or point-to-point wire the same circuit.
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Old 28th August 2009, 11:26 PM   #3
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About 6 years ago, I copied a Leak Stereo 20 schematic and it sounded fantastic. There's something special about the sound of PP, cathode biased EL84's. I found it was quite noisy with a 12AX7 for the LTP, so I used a 12AT7 instead. There are no UL taps on those trannys....just use a 330 ohm to 1K ohm resistor between the screens and the B+.
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Old 29th August 2009, 07:55 AM   #4
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I found it was quite noisy with a 12AX7 for the LTP, so I used a 12AT7 instead.
Was there ant particular changes made to the circuit to do this?
Jeff
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Old 29th August 2009, 08:55 AM   #5
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Default el84 amps

I have all the circuits and details for the Mullard 5.10.

Eme if you are interested.

Hugh.
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Old 29th August 2009, 09:10 AM   #6
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This sounds good considering its simplicity. Needs a bit of modification for EL84
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File Type: jpg Self Splitter.jpg (40.0 KB, 120 views)
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Old 29th August 2009, 03:00 PM   #7
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I just finished the Oddblocks project at www.Diyaudioprojects.com, which uses this type of CCS arrangement with a LM317 as a self inverting circuit. It sounds fantastic! I have never seen it using 2 CSS like here, I wonder what the purpose of x2 LM317's serve?
I think if I were to go this route again I woud use Bruce Heran's design for the EL84. Thanks though, again a very interesting design.
Jeff
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Old 29th August 2009, 03:13 PM   #8
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I was wondering if it would be possible to use the original Eico HF-81 circuit from the phase splitter through the OPT's and just using a simple SSRP in front of the phase splitter, maybe using a 12AU7 or 5670 or similar.

Here is the original circuit:

http://home.earthlink.net/~eico_hf81...matic_full.gif

Any thoughts?
Jeff
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Old 29th August 2009, 03:16 PM   #9
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Was there ant particular changes made to the circuit to do this?
Jeff
Not really. Use a CCS at the tail.
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Old 29th August 2009, 03:28 PM   #10
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I built Eli Duttman's El Cheapo/Bargain Basement with a pair of salvaged Sherwood transformers. It is thoroughly modern (not too much gain and/or nfb like older circuits), and it is awfully simple (you do need to assemble the CCS's on a breadboard). Mine sounds great! If you want to avoid NFB, you might look at Poinz' Musical Machine.

pj
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