![]() Ofcourse the cap doesn't contain any signal but it wil set the frequentie handling of the tube. So, all what I could think of is the goal of de the bypass cap for AC level, ie raising the level of a specific frequentie range passing through the tube. (680nF) I aspect Marshall chose a (signal) cap because you can't find a electrolytic cap that small. It set me to thinking and then also realising that Marshall uses oft (bipolar signal) caps as a cathode bypass. The bipolar electrolytic caps in a German amp which I had for repair. Just that, as you mentioned in quote, made me earlyer confused when I saw But since the tube has no way to pull the cathode below ground, thus pulling the capacitor's posative terminal negative, there is no danger of reverse polarity across the bypass cap. Looking at the cathode bypass cap, we see there us both a DC component and an AC component to the signal present across the cap (and I think this is where some designers get confused). A good example of this is a passive speaker crossover network. When an electrolytic capacitor is used to pass or couple an audio (AC) signal, where the polarity across the cap alternates between forward and reverse, a non-polarized capacitor is mandated. But the AC component sits on top of the DC component, and its magnatude is such that the positive terminal of the capacitor never comes close to crossing over the 0V line into negative voltage terratory. A good example of this is the power supply filter cap here, you have both a DC component as well as an AC component (ripple voltage). In other words, the voltage on the plus terminal must always be more posative than the voltage on the negative terminal, regardless of whether the voltage across the cap is AC or DC. The standard (polarized) electroylytuc caps don't like to see reverse polarity. The RCA sockets aren’t gold-plated and the circuit itself is balanced to express the designers’ emphasis on fully symmetrical operation.IMO, usign bipolar caps for the cathode bypass is just misguided engineering. The overall construction is very solid and draws attention with its oversized power supply, discrete volume control circuit and Mosfet-based buffering and voltage gain. Polypropylene caps nicely decouple the power supply rectifier diodes. Adjacent are many filter capacitors of varying sized including 6 x 10.000uF audio-grade Nover units and 14 smaller Rubycons. It consists of many multi-stabilized and filtered stages powered by a Hegel-made triple-secondary toroid. This accommodates a recording device, external headphone amp or subwoofer.Īs already stated, the power supply section is extremely sophisticated. One of the RCA outputs has jumpers to select between variable/fixed output. Here we see traditional thru-hole construction to rely on premium parts like metalized precision resistors of ultra-tight tolerances. ![]() This circuit is based on Hegel’s proprietary SoundEngine concept and consists of two complimentary 2SK2013/2SJ313 Mosfet pairs in a balanced arrangement. Those promise significant current reserves. ![]() Here we find pair-matched mid-power transistors. Post attenuation the signal meets the voltage gain section placed close to the rear panel. This array is surface-mounted and powered from a discrete transformer secondary. First the signal enters one of the smaller PCBs mounted above the mother board for the volume control, a nice black Alps potentiometer that’s outside the signal path to merely control a resistor array triggered by transistors. Hegel states that the signal in their preamplifier runs through only two transistors and between one to three resistors. The big use is in speaker crossover networks. It is used where you want the price and volume advantages of an electrolytic, but have AC current that crosses 0v. That way you get a polar cap with out poles. This review page is supported in part by the sponsors whose ad banners are displayed below A bi polar cap is really two polar caps cross connected, - to+ and +to. ![]()
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