looking for fairly simple project for Eico 81 OPT's

[jmillerdoc]

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]

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]

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]

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]

el84 amps

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

Eme if you are interested.

Hugh.

 

[Shoog]

This sounds good considering its simplicity. Needs a bit of modification for EL84

 

[jmillerdoc]

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]

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/schematic/eico_hf81_schematic_full.gif

Any thoughts?
Jeff

 

[TubeHead Johnny]

Was there ant particular changes made to the circuit to do this?
Jeff

Not really. Use a CCS at the tail.

 

[pjanda1]

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

 

[Shoog]

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

By using two LM317's you fix the standing current in both valves which avoids core saturation in the OT. It never needs adjustment. The caps allow the differential nature of the output to be preserved.

Shoog

 

[DougL]

If I was looking for a project that used 8K:8 transformers,
the one I admire most is http://syclotron.com/?page_id=3, SY's RED LIGHT DISTRICT. Solid engineering, clear documentation. Looks like a straightforward build. no exotic parts.

Doug

 

[Shoog]

If I was looking for a project that used 8K:8 transformers,
the one I admire most is http://syclotron.com/?page_id=3, SY's RED LIGHT DISTRICT. Solid engineering, clear documentation. Looks like a straightforward build. no exotic parts.

Doug

Doesn't sound very special though.

Shoog