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Old 7th February 2008, 02:34 AM   #11
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[QUOTE]Originally posted by tubelab.com
[B]

I am building one because I can

The only reason I am not building one right now is becase I can't...
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Old 7th February 2008, 03:02 AM   #12
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Quote:
The only reason I am not building one right now is becase I can't...
Thats OK. You (and most of the readers on this forum) can let us figure out what works and doesn't work, and blow up a few (OK lots of) parts. The working stuff gets posted and some of the circuits will make their way into stuff that you can build.

Seriously, I can remember someone giving me some monster Heathkit OPT's for KT88's back in the 1970's. I set out to design a state of the art direct coupled P-P power amp. After blowing up several 6550's and KT88's, I gave up and passed the transformers on to a friend who used them in a guitar amp. I would love to have those OPT's today. I now have 30+ more years of electronics experience and a couple of college degrees, and I still blow stuff up, especially when playing with SMPS's fed from the power lines.

I doubt that any 250 WPC tube amp will ever be reduced to the simplicity and with the success rate of a SimpleSE, but the lessons learned with the big stuff can be applied to smaller tube amps to improve them.
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Old 7th February 2008, 03:25 AM   #13
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Quote:
Originally posted by tubelab.com

The regulator design is easier if the pass device is is series with the negative side of the rectifier bridge (or transformer CT). The cathode (source) is grounded and its drive is ground referenced. My experiments used an IRFPG40 N channel mosfet rated at 1000 volts and 4 amps of drain current.

Maybe a little easier, but the output impedance and ripple rejection is much worse.
The power supply chassis the the first part of the amp I'm going to build (I have nearly all the parts already). I'll get stuck into it this weekend (have nothing else planned) and post up the schematic. I've done this before, so the PSU circuit is already 90% drawn in my head

The pass element will consist of five parallel 12E1's, each cascoding a BD681 darlington emitter follower - grid connected to the emitter, cathode to the collector, anode to +700V (this is for just one channel, supplies will be independent).
This way you get the low output impedance of a biploar emitter follower while the valve dissipates (nearly) all the heat.

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Old 7th February 2008, 03:49 AM   #14
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BTW - nice Mopar
I'd like to build a hot rod with one of these engines one day (especially an "elephant" engine)........
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Old 7th February 2008, 04:08 AM   #15
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Got an email back from Hammond - List price of the 1650W is $389.58 AUD each plus (10%) gst.

Turns out that I don't live far from Hammonds Australian warehouse, so atleast I won't have to foot the freight bill to my front door (they're 28 Lbs each !)
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Old 7th February 2008, 05:58 AM   #16
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There is a higher power and higher bandwidth alternative. Though shipped to AU Im sure its a pretty penny.

400W toroidal OPT. Supports 8 KT88.

$408.35CAN, 10.65Kg.


Edit: Whoops, not UL.
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Old 7th February 2008, 07:00 AM   #17
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Quote:
Originally posted by tubewade
I admire you guys for building giant amplifiers like these, ..... I already have amplifiers that are too big to be of practical use in the living room.

I'm the 2nd nut who has built several monster amps and somehow get to listen to them......strong man to lift'em too with extra bracing in loft floor.
Series pass tubes in psu wouldn't hold up without consuming more heater power. Chassis big enough as it is.
My cue to the psu would consider pfc boost converter, esp when uprocessor would be on board. Complexity ?

richj
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Old 7th February 2008, 07:17 AM   #18
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I regularly contemplate hi-po tube amps as bass heads for my rig. Then sense takes over and I leave it alone. I don't want to have to hump it in and out of gigs along with my mudmagnet speakers. Contemplating a very small tube amp on the end of the preamps to give a similar O/D effect.

For hifi, I fail to see he point except for the 'because I can'.
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Old 7th February 2008, 08:36 AM   #19
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I started out working / building stuff in/for chemistry and nuclear physics/fusion research labs (495kW RF generators with 10kW drivers, ROTOMAK's, racks/rooms full of charged 16kV capacitors, 5V to 100,000V variable regulated power supplies, 8W lasers, etc, etc.

This amp I'm building now is neither complex nor big (well from my perspective anyway especially compared to some of the other things being built up in my shed)!

Attached below are a few crappy conceptual drawings of how Im going to construct this amp. (No dimensions added yet and the scribbles are not really to scale, but they should give an idea.)
The amp will stand upright, like a tower, probably 1 to 1.5m tall. It will be constructed around a TIG welded frame made from 50mm by 50mm aluminium angle 5mm thick. This frame will support everything, including the transformers.
Two varnished solid pine bits (15 or 20mm thick) will form the side panels and the legs. The front panel will be cut from 5mm thick aluminium sheet either painted or powder coated gloss black. The lower section of the front panel will consist of a big Conrad heatsink for the heater supply regulators, behind which the numerous power supply toroidal transformers will live.
Nearly all the electronic circuitry and all the valve sockets will mount on various sub panels attached to the main frame, about an inch from and parallel to the inside surface of the front panel. All tubes will mount horizontally, poking out the front panel.
The front panel wont actually provide structural support for anything, being easily unscrewed for servicing access. The rear panel will be cut from a sheet of pegboard, with flyscreen wire glued to the inside surface, over all the holes. This will ensure adequate internal ventillation. As for the top panel, that will just be another pine sheet.
The aluminium angle frame will be fitted out with pneumatically riveted Nutserts for screw mounting of all the panels.

BTW, ~250W per channel for HiFi use driving not-so efficient speakers with high dynamic range material at reasonable listening levels (but still avoiding clipping) is much less over the top than many people here might imagine.
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Old 7th February 2008, 08:40 AM   #20
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A drawing of the front. There will also be a vintage style pair of current and voltage monitoring meter movements, switchable between the various anodes, cathode, etc and several blue leds.
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