To mount power devices onto a heat-sink, you need the appropriate mounting kit which comprises a top-hat shaped plastic washer/spacer and a special insulating "sheet" made I suppose of some sort of silicone rubber which is slightly larger than the device and of course a 3mm screw, washer and nut. These are available from the usual sources
Note that it is most important very carefully to de-burr the mounting holes in the heat-sink to obviate the risk of short circuits. I have blown up enough high-voltage regulators for one lifetime; I became so neurotic about it that I used to buy 317s in 25s and used an old Megger tester to check the insulation, An ohm-meter is not enough!!
Paul
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Joined 2009
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Hi Bjarne, Thank you for the feedback!
Hi Bigun,
The preamp that Bjarne tested is a 2A3.
The filament supply quality with a 2A3 requires the same care as every other filament!
With ac, you get large amounts of 50/60Hz sidebands, and 100/120Hz sidebands from distortion cross-products. And you will have difficulty filtering out the broadband mains noise. This is not HiFi.
With the 3-terminal dc regulators (I believe the DIYHFS is based on these) you have the usual problems of far too much noise from the IC reference (see previous posts, above), and, worse still, the cathode current (music signal) is not properly isolated from the IC control loop.
Sure, with a 2A3, the raw HUM level is lower, but that's not the same thing as high quality sound - as Bjarne has just found!
Hi Bigun,
The preamp that Bjarne tested is a 2A3.
The filament supply quality with a 2A3 requires the same care as every other filament!
With ac, you get large amounts of 50/60Hz sidebands, and 100/120Hz sidebands from distortion cross-products. And you will have difficulty filtering out the broadband mains noise. This is not HiFi.
With the 3-terminal dc regulators (I believe the DIYHFS is based on these) you have the usual problems of far too much noise from the IC reference (see previous posts, above), and, worse still, the cathode current (music signal) is not properly isolated from the IC control loop.
Sure, with a 2A3, the raw HUM level is lower, but that's not the same thing as high quality sound - as Bjarne has just found!
Hi Dennis, It's easily explained - the filament in a DHT is the same thing as the cathode. So the music signal runs through the same internal wiring as the filament current.
Meanwhile, the Heat-current is controlled by some kind of regulator that reacts to its own incoming supply. Any irregularities in the DYNAMIC heat current are imposed on the music. So we must allow only the minimum noise into the heat current, and no component-induced artefacts into the current either. This requires extraordinary care in the design of the regulator, because our ears are so sensitive to signals/noise that have no origin in the music.
Some folks have amps and ears that can discriminate the effect of components that have only a minor influence on this - and here is an example!
That makes sense Rod. I know I experienced that in my John Hogan 300B with hum pots. Even though the amp sounded wonderful, there was always, to my ear, noise other than hum coming through. I have everything layed out on my bench to finally complete the boards, but the stuff is SOOOOO dang small, I have to work my nerve up to assemble them. Now I am up against a dead line to have this amp done by the end of the month....that helps.
I just can't fit a full-blown LCLCLC supply into the chassis and had some MJE15032 lying around so built a quick breadboard CCS ring of two for heating 2A3 . I don't think the MJE15032 is a good choice and seems to require a good few volts across it = lots of heat . Are there any better biploar transistors than the MJE15032 recommended for heating 2A3 ?
316A
316A
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Joined 2009
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I like the sound of this.
Is it possible to configure your regulator for a 2A3 and then easily re-configure it for a 6A3 ?
The generic name is "shoulder washer", but that includes any of that shape.
All the best,
Chris