If I wanted to build an SR45...

[jrebman]

Paul,

Yes, a lot of the east coast was hammered.  A couple feet of snow in Philly should bring things to a grinding halt for about a month :-).  I grew up not far from Philly and that much snow is tantamount to a national disaster there.

-- Jim

[xcortes]

There was an article called the "Simple 45" that was a 45 version of the circuit that John Tucker and I developed back on the late 90's for 2A3s. It does not use shunt regulation, and it was direct coupled with the active loaded driver tube sitting "under" the 45 tube. It was originally published in VALVE (which I hope to publicly archive on the Bottlehead site some day) and I believe it may currently be available through the Enjoy the Music website.

It's on positive feedback:

http://www.positive-feedback.com/Issue1/single.htm

The article doesn't call it "Simple". I think that was a nickname it got later. Cool and "Simple" amps that sound very nice (I built a pair which I later dismantled to cannibalize some parts).

[2wo]

Damn, just lost my post, I think if someone is replying while you are typing the forum drops yours, or something.
Anyway, I would like to build a SR-2A3, maybe using a 6V6 at the shunt tube. Paul, if you have any hints it would be appreciated. I often plug in a set of new 2A3’s to save my NOS 45’s for critical listening. The 2A3 sound surprisingly good at that operating point.
I live in Valley Forge Pa. (just west of Philly), we got about 14”, unfortunately we are getting kind of used to it…John         

[jrebman]

John,

And I'm here in Boulder and it's 64 degrees and sunny out.  We've had almost no snow at all this year, and temparatures more like Seattle area -- 40s/50s.  I've been here 16 years now and this is by far the most bizarre winter we've had.

An SR 2a3 sounds lovely too.

-- Jim

[Paul Joppa]

To make a SR 2A3 you need a minimum of 80mA supplying the shunt regulator - more is better. Regulated voltage will be (let's say) 380v. Allowing 5% compliance and another 20% for possible power line variations (+/-10%), the current source feeding the regulator must dissipate 9 watts, minimum. If your power supply voltage is a bit higher than optimum, it will be more. You can't reliably dissipate that much power with a TO-220 transistor unless you have a very large heat sink - around 10 cubic inches volume, and well ventilated for convection cooling. Incidentally, you must allow for the possibility that the mounting washer will fail, placing the heat sink at 400-500vDC, so it must be protected from accidental contact - without interfering with the ventilation.

That's an example of what I meant when I said "The issue is mostly the voltage and power dissipation capability of available transistors in the current sources" in a previous post in this thread. All these are solvable problems, but it would take a lot of engineering time to solve them in a safe and reliable way.

[Paul Joppa]

It's on positive feedback:

http://www.positive-feedback.com/Issue1/single.htm

The URL is "...single" maybe that's how it got that name.

[awsjr]

Doc, Xcortes - that's the one...single / simple, looks like a nice 45 amp to build....thanks Paul for the history of the cp-06006....actually I think I bought those from Xcortes....Jim - you can not go wrong with the SR45...it is a fantastic amp....I switch between my 2A3 Horus w/ exo-36 cobalt OPT's (see the Magnequest site) and the SR45 and the SR45 every bit as good....

[jrebman]

awsjr,

Thanks for the note and another thumbs up for the SR45.  The Horus has always been another of those amps that has caught my fancy, though I've never heard one, and from what I understand, the cobalt transformers are no longer available at all, so no need to worry about that.  The SR45 should make a fine match for my office system, which is where I do my serious listening and where all the best gear endss up.

-- Jim