THE AROMA OF POWER SUPPLY CAPACITORS
CHECK OUT ALL ELECTRONICS INC
THIS ARTICLE IS WRITTEN FOR EXPERIENCED
KIT BUILDERS WHO KNOW HOW TO HANDLE HIGH VOLTAGE,
AND KNOW HOW TO DISCHARGE CAPACITORS.
In the 1970s while rummaging around in my most favorite place to spend Saturday afternoons Canal Street, near the southern tip of Manhattan, a surplus electronics Heaven, I discovered high voltage capacitors used in strobe flash units. They cost $1 each and compared to the price of comparable capacitors they were dirt cheap, so I started to experiment. Most of these were 360 volt so I had to put them in series which doubled their voltage rating and halved their capacitance value. I loved the way they sounded in my tube amplifier power supplies, and they sounded very different than the "normal" computer grade capacitors for a good reason: they were intended to work very differently, meaning their discharge rate.
Photoflash caps are designed to completely discharge and charge very quickly, while computer grade capacitors are designed for constant current running through them and charge and discharge much slower. The "stuff" inside them is chemically different. As you know your power supply is constantly charging and discharging, just like a photoflash.
At this time I was using tube amps that had solid state rectifiers so charging these big capacitors was not a problem and I used twenty of them in my bass amplifiers to produce very exciting bass dynamics.
Many years later I discovered that Julius Futterman also used the same photoflash capacitors in his amplifiers, and in my search for a better capacitor, I couldn't find one for this circuit in terms of sound. At New York Audio Labs we used thousands of them.
WARNING: DO NOT USE HIGH VALUE PHOTOFLASH CAPS IF YOU USE A TUBE RECTIFIER.
It was obvious that the "aroma" of the power supply capacitors made a big difference in the ultimate quality of an amplifier, which is why in the Moscode amplifiers I offered a "Maxi" version, which used a very large polypropylene capacitor in parallel with the large computer grade capacitor in the output stage. This made the amplifier sound smoother.
The question then arises for the DIYer is what capacitors to use in tube amp power supplies. The answer depends on the type of rectification you are using. If you are using tube rectification you can not use large value power supply capacitors without damaging your rectifier because of the large current demands of the large capacitor's charging and discharging will strip the plates of the this tube.
On the other hand if you are use state rectifiers you can go gonzo with photoflash capacitors.
When you go to All Electronics web site you will notice that they have great prices on computer grade, photo flash and oil capacitors. Each type has its unique aroma. The oil capacitors are the smoothest, and most natural sounding, but have the least "slam". The photoflash capacitors sound smoother than the computer grade, but you must connect them in series with a high value 270K balancing resistor from the plus and minus terminal of each.
When you get these capacitors DO NOT use them at full voltage, until you age them at 50% voltage for 24 hours.
You may have to use an outboard chassis to mount these capacitors, and then connect them to your amplifier with an umbilical cord that can handle the voltage and current. Make sure you use a bleed resistor so that these capacitors discharge when you amplifier is off BUT REMEMBER THEY MAY STILL HOLD A CHARGE SO BE CAREFUL WHEN HANDLING THEM AND DISCHARGE THEM WITH A 100 OHM RESISTOR BEFORE HANDLING THEM .
Am I suggesting that you can change the personality of your amplifier by changing the "mix" of your power supply capacitors?
I remind you that I only use Jensen oil power supply capacitors in my personal hot rod amps on the output of my tube regulated power supplies.
CHECK PAGE 66 AND 67 of catalog. You can use 4 of the oil motor starter/run capacitor 12 mfd 600 VAC with a tube rectifier. CAT #MRC-1266 at $3.50 each. Photoflash caps cost between $1-2.50 each . the 2400 uf at 450 cost only $4.50 and this is perfect for 300B power supplies using solid state rectifiers. All of these is a great bargains.
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