Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: Doc B. on May 17, 2012, 01:25:13 PM
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Just a notice that Eileen was packing S.E.X. kits to go out today and not only got caught up, but she also has one extra one ready to ship today.
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I'm interested in building a SEX monoblock with only the best components. Is this possible. Purpose is to use one to test horn speaker designs. Long term plan would be to build second block down the road. I prefer the amp to be close to the speaker. Any thoughts are appreciated.
Dave
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Yes, absolutely!
You could use one side to build out essentially the stock circuit, then throw a 6V6 in the other side to use as a shunt regulator. You would need a Speedball board to feed the 6V6, and a C4S board with the TL431 pads to implement the regulator, and a different operating point since you will lose about 30V through the CCS/Regulator.
I believe PJ has been wanting to try this for a long time, hopefully he chimes in.
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I was never able to come up with what I thought was a sensible version of a shunt-regulated monoblock SEX amp. By that, I mean a version that I would expect to sound better. You have to make compromises that impact distortion and power, in exchange for regulated goodness, so it would sound different; better in some ways and worse in others.
A reduced-power version, perhaps 1.5 watts, would be easy, keeping the original circuit but reducing the voltage with the regulator. A more powerful version would best be built around the 6EM7, which is to my ear an inferior tube. I know I've worked something out a couple times before. I never documented my notes because I wasn't happy with the result, but I'll dig out the pencil sketches if anyone really wants to experiment with it.
A much better idea in my mind would be a shunt-regulated 45, which I have been working on at a slow pace for a few years. Some recent developments have made that more practical.
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Doc,
Can you/Eileen hold it for me - for the next three days?
If not no worries. I need to place my order so I have it for Christmas break (14 days).
Cheers
Stephen
Wormwood
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Eileen will be happy to give you an update on the current inventory when we are back at the office tomorrow.
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Thanks Doc.
I forget it's only Sunday there - Living the Monday midmorning right about now.
Stephen
Wormwood
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Doc,
Would there be any update from the Lady Eileen?
Cheers,
Stephen
Wormwood
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Thanks for the comments fellows. Paul, I find the 6EM7 to sound brutally honest, sonically. Would you be open to it's implementation outside the parafeed circuitry ? I frankly considered it my choice for the S.E.X.
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The 6EM7 can work in the SEX amp, there's a cathode resistor/bypass capacitor change, and ultimately it works best with the C4S upgrade with R1 set to 1000 ohms.
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Now that it comes up, I don't think I ever revised the operating points for the 6EM7 in the Version 2.1 (current version). Very few (PB is one) actually tried it, and the feared shortage of 6DN7s has not materialized, so I put it on the back burner. I'll try to do that this weekend, for those who love the 6EM7. They will be only a little different from the old version 2.0 values, but we might as well take our best shot!
The biggest problem with the 'EM7 is the high plate impedance of the driver section; I'll see what I can do to get the driver current up a bit. I don't think I've ever heard one with the new (v2.1) output transformers and plate choke - should be interesting!
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Yeah, I finally got my ears on a 2.1 last week, quite a surprise compared to the old model!
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Great. I'm interested in a "tricked out" 6EM7 "SEX" with realistic pricing. Thanks fellows !