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-   -   looking for fairly simple project for Eico 81 OPT's (http://www.diyaudio.com/forums/tubes-valves/150208-looking-fairly-simple-project-eico-81-opts.html)

jmillerdoc 28th August 2009 05:28 PM

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

Tom Bavis 28th August 2009 07:00 PM

Quote:

Originally Posted by jmillerdoc (Post 1909156)
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.

TubeHead Johnny 29th August 2009 12:26 AM

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+.

jmillerdoc 29th August 2009 08:55 AM

Quote:

Originally Posted by TubeHead Johnny (Post 1909430)
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

ecc83 29th August 2009 09:55 AM

el84 amps
 
I have all the circuits and details for the Mullard 5.10.

Eme if you are interested.

Hugh.

Shoog 29th August 2009 10:10 AM

1 Attachment(s)
This sounds good considering its simplicity. Needs a bit of modification for EL84

jmillerdoc 29th August 2009 04:00 PM

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

jmillerdoc 29th August 2009 04:13 PM

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

TubeHead Johnny 29th August 2009 04:16 PM

Quote:

Originally Posted by jmillerdoc (Post 1909651)
Was there ant particular changes made to the circuit to do this?
Jeff

Not really. Use a CCS at the tail.

pjanda1 29th August 2009 04:28 PM

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
www.wildburroaudio.com


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