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4 minutes ago, sandyk said:

 

In the 2nd and 3rd photos from the top, the electrolytic capacitors are too close to the valves and will have a reduced service lie due to the heat.

Unless there's enough meat in the caps to last years, unless that is.

 

That's one reason not choosing tube gear, the heat build up affects not only caps, but insulation materials, those 1950's jobs don't have the insulation of today with Teflon for example. Heat will break down and crumble early bakelite stuff. The low voltage (up to 1500V DC) just adds to the mix. If you like the tube sound, fine, but consider the downsides.

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  • 3 weeks later...
12 hours ago, Sam Lord said:

 

 

Ventilation certainly helps longevity, even with massive heatsinking.  But for components using less than about 30 watts in a full-sized (1RU or bigger) unit, I wouldn't worry.  A bigger concern is with internal parts which lack bolt-on heatsinks.  I've seen many parts like TO-220-cased regulators and transistors that have no business operating without heatsinks.  A basic LM317 regulator is rated about 15 times higher dissipation when well-sinked compared with unsinked operation. 

A regulator fitted to a grounded heatsink is an open invitation for high impedance leakage currents to form. 

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11 minutes ago, sandyk said:

 

Adhesive Silicon Washers or Mica washers should reduce this ? .

 Other than  the 78XX , most adjustable voltage regulators need to use them as the metal tab is not the 0 volts connection. 

My experience is with 300A+ Power transistors. Even though the base is metal, the interior silicon stack forms a capacitor between the substrate and the metal. This propagates RF when the transistor switches in a PWM fashion about 1kHz and under. For HV applications 3300 V-11,000 V, the heatsink floats above ground to avoid common mode noise output. Mounting is via ready made heatsink wafer or a thin layer of silicon paste applied with a paint roller.

 

This is an older 3rd gen IGBT.

Image result for 300A Power IGBT Fuji

 

 

2MBI400VD-120-50.PDF

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On 1/27/2018 at 7:37 AM, sandyk said:

 

How about something like this?

Incidentally, the John Curl Blowtorch Preamp part 2 Thread in DIY Audio , now has almost 100,000 replies !!!

 

Click on the image twice for a much larger image.

John Curl's Blowtorch Preamplifier.jpg

 

That's a Lumin xx1 series. There's minimal power losses in that design, 25W , tops, so the heat is dissipated through the solid aluminium easy enough.

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1 minute ago, sandyk said:

 

 My mind boggles at the thought of applying heatsink paste with  a paint roller  ! :o

 

Are Aussies the only ones who don't put a space between " heat"  and "sink" ?:D

 I often  do to avoid nit picking by the U.S. members.

I use heatsink, spell checker hates it, never mind!

 

For routine maintenance, the Xeon workstation's heatsink paste is removed with WD40 and a rag, let to dry. Bunnings have a very small paint roller, it's only about 20mm wide, just perfect, takes a bit of effort to get the paste onto the roller, but you can't beat it for providing an even amount of paste. Just paint on until the top of the processor until the grey is gone, done!

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  • 2 years later...

Nothing wrong with bare wires internal to equipment. In normal use, access to the inside is by the way of a key or tool, totally legal.

 

Problem is, the right hand connection has split the plastic, under the right circumstances can track to the outside from the bare terminal. There is quite a bit of kit removed on the mains board, or bypassed, you can see the original connections at the hot and cold points on the board.

The bare copper wires can be come loose at the board since the split can get wider. In the case of semiconductors soldered directly on boards, there's heat expansion through years of power cycling that causes the solder to come adrift from the pads and the music stops.

 

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17 hours ago, mansr said:

Yes, that particular contraption would fail compliance since it has no safety ground and can hardly be considered double insulated. The stiff wires are troublesome as well.

 

More broadly speaking, exposed metal with dangerous voltages can be legal if it doesn't endanger the user during normal operation. Consider, for instance, a toaster. Now, regardless of legality, using bare wires where insulated ones would work just as well is poor design, reckless even, something the people defending this monstrosity seem not to realise.

Surely you jest at the Marantz in the photos above are original construction? 

 

The original Marantz CD player would have been compliant when it was submitted to approval authorities,  one owner who changed the power inlet and added the bare wires, voided that compliance.

 

Just because there's no safety ground now doesn't mean there was one in the first place either,   many sources don't have one. 

 

In any case I've yet to see an IP21 rated tube amp with the cover off with voltages at 350V dc ++, so where do you provide compliance with  that. Same legal nonsense as before. 

 

If you open any cover on live equipment, then welcome to the  Darwin awards. 

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