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OK, I admit it. You can calculate circuit values until the cows come home but sometimes it's so much easier and faster to just dial it in. I've been a ham and involved in engineering for over 35 years, and I gotta tell ya,
these are undoubtedly some of the most indispensable tools I have ever had.
With the low and high value Resistor Sub Boxes, rather than providing resistance decades like most resistor sub boxes do, I decided to provide 45 of the most common values on two rotary switches. It seemed more practical to use the standard values we would most likely incorporate in the amps. The resistors are metal film and are rated at 1/2 watt. For the Capacitor Sub Boxes, I decided to provide the most common values that we typically see in guitar amps. Just like the resistor sub boxes, it seemed pointless to include some oddball values that we wouldn't use anyway. The poly caps are rated at 630VDC, the ceramics are 1KV. The electrolytic caps in the ECC-HV type Sub Box are rated at 500 volts DC, and are 105 degree C parts, while the electrolytics in ECC-L type Sub boxes are rated at 50 volts and are meant to be used for experimenting with the capacitor value in cathode bypass caps in preamp and power amp circuits. The LSUB Inductor Sub Boxes are rated at 200ma and 400ma, although I wouldn't run them all day at that current. The units are meant to be used for temporary insertion in a circuit while developing your high voltage supply. The inductance ranges are 0 (straight wire) to around 16H and zero to 10H. The RSUB Power Rk-Ck Sub Box is used for dialing in cathode bias by substituting it for the cathode bias resistor in a cathode biased output circuit. The box includes two terminals to connect an electrolytic capacitor in parallel with the cathode resistance. The rheostat is rated at 500 ohms and 25 watts. The Rk-Ck Preamp Sub Box has both a pot and a selection of 12 different electrolytic capacitors in parallel with the pot for dialing in the cathode bias components of a preamp stage. The electrolytic capacitors are rated at 50 volts, and the pot is 2 watt, 5K linear. The High Power Resistor Sub Box has a 47K 5 watt pot. With it, you can quickly dial in the dropping resistors in your high voltage (B+) power supply chain for the screens and on down the line. The Low Power Resistor Sub Box is a 50K, 2 watt wirewound pot you use for final tweaking in the power supply chain feeding the preamp stages. Believe me, tweaking this way and dialing in a sweet spot will just make your jaw drop, it is so easy and fast. I realize these are unregulated power supplies, but getting it close and 'nominal' by this method saves a ton of time. And finally, the C-Cap Sub Boxes are full wave or full wave bridge rectifiers with adjustable sag so you can emulate a tube rectifier of a certain type in the development of your high voltage circuit. The C-Cap Sub Box is adjustable from a 5Y3GT to a straight SS (no sag) rectifier and everything in between. For instance, if you determine by the setting on the C-Cap Sub Box that your amp sounds best between the setting of a 5V4 and a 5AR4/GZ34, you can use a 5AR4/GZ34 with a power resistor in series to split the difference between the two. The label on the C-Cap Sub Box indicates the approximate resistance between straight SS through and including a 5Y3GT, so you can do the math easily to determine that series resistor value. This box is about 1/4" taller than our copper cap module since it contains a rheostat. It also has two mounting feet on both ends, the same as the copper cap module. It may be installed in an amp permanently and used as an adjustable-sag rectifier. The only issue is that the rheostat has a wiper and might move some due to the vibration in a combo amp or in a head sitting on a speaker cabinet. You could experience some slight noise or scratching sound if that occurs. |
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