And likewise with myself. Indeed, I will admit to having a flat spot that is somewhat flatter that in used to be. Still, its worth it from a progressive (not flat spot progressive…although, hmm) view point.
Best,
Shane
The OA3 is used to drop the B+ voltage to the preamp tubes only, so very little current is invloved. Buf of course the "no heat loss" part is an exageration, perhaps he was just referring to the heat loss of the resistor, in any case, it's just the usual marketing BS!😀 This is what he said in the Decware forum:
"Of course to feed the preamp stage (smaller tubes) we need to drop the voltage and the common way to do that is a high wattage resistor followed by a small capacitor. That is how the Torii Mono's were done. In this amp, I am replacing this resistor with a vacuum diode aka voltage regulation tube (OA3) which will give me the same voltage drop as the resistor but with 20 times the ripple reduction and 100% decoupling so that harmonics from dirty power grids in your city do not contaminate the pure DC power feeding your critical preamp stage. This also means that again 100% of the heat has been eliminated."
For preamp tubes, I don't think you need that much current, so for the OA3:
75 x 0.005 = 0.375W, where 5mA is the minimum current required for the VR.
It was the amount of heat that was the surprise, not the calculated dissipation.
Its not like the stabiliser tube is much of a heatsink. I wonder if it has something to do with (lack of) copper loss. ??
It was claimed by the guy that made my "600 watt" computer speaker system. The satellites use 3 inch drivers, and the subwoofer is maybe 6 inches. It's all powered by a 12 volt linear power supply that is maybe 2 amps max. The whole "system" cost me $40 new (20 years ago). It does sound quite nice at low volume. My guess is 15 watts RMS total at 10% distortion.
Copper loss is not an issue at 5 or 25 mA.
3.75 watts are lost, whether it's in a resistor or a VR tube. The temperature difference is due to the surface area of the VR tube (about 5 inches) VS the surface area of a 5 watt resistor (about 1 inch). The VR tube IS a better heat sink than the resistor due to its surface area.
Note that some of the new tiny 1 and 2 watt resistors are made with modern materials that can run at temps up to 200C. This allows a 2 watt resistor in a 1/2 watt case size. DON'T flush mount them on a PC board unless you want a brown spot and a funny burning smell. If using them for PTP wiring, allow 1 inch lead length minimum, and crimp the wire joint before soldering. A tin - lead solder joint will brittle with age due to thermal stress. These were meant for modern no lead solder which needs 260C to melt.
I'd also watch out for the voltage drop across these tiny resistors. It's best to put several in series when using them in VT based equipment where voltages are considerably higher than most of SS work.
Many of these new resistors carry the same or higher voltage rating than their big brother counterpart.
I used some tiny resistors in a tiny guitar preamp I made about 3 years ago. It used PC board construction and the small 2 inch by 4 inch board contained 2 12AX7 tubes. Six resistors were laid side by side flush mounted on a home made PC board. Four resistors were conventional 1/2 watt resistors. Two resistors were the plate loads for a 12AX7 and dissipated about 1 watt each. I used 2 watt resistors from BC components that were about the same size as the 1/2 watt resistors adjacent to them. The exact part is no longer carried by Digikey, but there are several other vendors with similar parts.
The preamp worked great for over 2 years, but I discovered the discolored PC board when I was swapping tubes. I replaced both resistors, standing them about 1/4 inch above the other 4 resistors, swapped the tubes, and put the amp all back together. It still works good despite the brown spot in the board.
A quick scan of the Digikey catalog revealed that a resistor of the same size and specs is available from Stackpole and others.
I grabbed the spec sheet from Stackpole's web site, because it was the first vendor listed for a tiny 100K 2 watt resistor. The 2 watt version is rated for 350 volts working and 600 volts "overload". The dielectric coating is rated for 500 volts. The part is .43 inches long (11mm) and .18 inches in diameter (4.5mm). It is rated for 2 watts up to 70C and is linearly derated to 0 watts at 235C!
A cheaper, smaller part is available from Yageo. It is rated at 500 volts working, and 700 volts overload, but only goes to 155C. It is 9 mm long by 3.9 mm dia.
I used some tiny resistors in a tiny guitar preamp I made about 3 years ago. It used PC board construction and the small 2 inch by 4 inch board contained 2 12AX7 tubes. Six resistors were laid side by side flush mounted on a home made PC board. Four resistors were conventional 1/2 watt resistors. Two resistors were the plate loads for a 12AX7 and dissipated about 1 watt each. I used 2 watt resistors from BC components that were about the same size as the 1/2 watt resistors adjacent to them. The exact part is no longer carried by Digikey, but there are several other vendors with similar parts.
The preamp worked great for over 2 years, but I discovered the discolored PC board when I was swapping tubes. I replaced both resistors, standing them about 1/4 inch above the other 4 resistors, swapped the tubes, and put the amp all back together. It still works good despite the brown spot in the board.
A quick scan of the Digikey catalog revealed that a resistor of the same size and specs is available from Stackpole and others.
I grabbed the spec sheet from Stackpole's web site, because it was the first vendor listed for a tiny 100K 2 watt resistor. The 2 watt version is rated for 350 volts working and 600 volts "overload". The dielectric coating is rated for 500 volts. The part is .43 inches long (11mm) and .18 inches in diameter (4.5mm). It is rated for 2 watts up to 70C and is linearly derated to 0 watts at 235C!
A cheaper, smaller part is available from Yageo. It is rated at 500 volts working, and 700 volts overload, but only goes to 155C. It is 9 mm long by 3.9 mm dia.
smaller body, same dissipation, obviously the heat has to go somewhere ...
would it make sense to increase the mass of of connecting leads, like wrapping with copper wire ?
would it make sense to increase the mass of of connecting leads, like wrapping with copper wire ?
When I think of the "Doc" in regards to diy audio, I think of Bottlehead, not Decware.
Perhaps you are confusing them? Or perhaps I am?
I have followed the Bottlehead guys since they released their first amp kit and Dan S. (Doctor Bottlehead) was still repairing antique radios and publishing a short but interesting magazine called "Valve". In hindsight, it was the next best thing to Sound Practices at the time. I don't recall him ever claiming to be a hot shot design engineer. If anything, he was humble about his abilities. He had and has some pretty talented design guys on his team and seems to credit them appropriately.
His ad copy was and is clever, but I've never thought if it as "creative".
I do think of his products as creative, in the best sense of the word.
Perhaps you are confusing them? Or perhaps I am?
I have followed the Bottlehead guys since they released their first amp kit and Dan S. (Doctor Bottlehead) was still repairing antique radios and publishing a short but interesting magazine called "Valve". In hindsight, it was the next best thing to Sound Practices at the time. I don't recall him ever claiming to be a hot shot design engineer. If anything, he was humble about his abilities. He had and has some pretty talented design guys on his team and seems to credit them appropriately.
His ad copy was and is clever, but I've never thought if it as "creative".
I do think of his products as creative, in the best sense of the word.
I very well have mixed the two up... sorry 😱
Dan Schmalle = Bottlehead aka "Doc"
Steve Deckert = Decware
Thanks. I can see what you mean by heatsink - I'm wondering if its all to do with surface area, or if theres more to it than that.
The copper loss thing might not have been expressed correctly... with a resistor you have a solid conductive element (nichrome wire, copper, carbon or metal film, whatever it is).. and its the current through that conductor which creates the heat.
With a VR tube, if the current is passing between two electrodes using the inert gas as the 'conductor' perhaps it has less of a heating effect than something solid?.
Frequency dependant also, perhaps, slightly inductive?.. I've measured AC impedance at various AF when using them as Shunt's (0A2 and not 0C3), the impedance changing noticeably with frequency, would you suspect this would add to the temperature created if dissipation (W), and radiating envelope surface area were constant?, and would you expect the size and spacing of electrodes to play some part?
Again, thanks.
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I have owned a Decware Zen Select SET amplifier for years and I still love it to this day. Everyone knows that it's the sizzle that sells the steak, I cannot blame the guy for catering to his customers. Most of the complaints here seem to be that the marketing is geared towards audiophiles and not audio engineers. The amp looks aesthetically pleasing and very well built from the pictures. The transformers and PS look impressive. I am not sure if it hits the rated 38 watts while in class A but it might. His amps also come with lifetime warranties if you are the original buyer and great support. Something that is rare in this day and age.
But this is more like someone playing a recording of sizzle while dropping spam onto the plate.
(It's one thing to talk up your product (cook a steak in view/earshot of the customer), but it's another to just make things up)
edit- Just wanted to mention, it does look like a nice amp, and using "spam" above was just to make a point about that style of advertising.
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