DIY Hi-Fi Supply Modules | Tentlabs Modules
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Tentlabs Negative Bias Control
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PURPOSE
Power tubes need to be biased at a constant current to achieve optimal performance of the amplifier. Both cathode and fixed bias methods suffer from the fact that the current depends on tube age and mains variations, not to mention the aging of other passive components.
As a solution, servo circuits have been applied in many designs, but the amount of bias of these supplies all depends on the music signal and as such the bias current drifts with the music played, which is unwanted.
The new Tentlabs / Vanderveen circuit offers rock solid bias, independent of tube aging, music signal or mains power voltage changes. The module biases up to 4 tubes at exactly equal currents, with the setting of only 1 trimmer. All classes of output stages can be biased, A, AB or B, triode, tetrode or penthode, single ended and push-pull.
Result areas are:
- better imaging and stage due to lower hum and noise levels
- better bass due to near perfect (<1% error) current matching in push-pull stages
- Better resolution and imaging due to optimized left / right channel matching
TECHNOLOGY
Module contains an integrated negative bias supply, which is properly filtered and stabilized to achieve a clean bias voltage. A measurement section for each tube measures the actual current around a very small window around the bias hence is not affected by any music signal.
The maximum output voltage is -160V, enabling the use of virtually any tube up to a 211 or a 845. Every tube can be biased up to a maximum of 175mA. The outputs of the module provide linear and low output impedance to avoid interaction with the preceding driver stage driving the power tubes. Each of the 4 outputs can sink and source 1.5mA, allowing the use of relatively low grid resistors, if required.
The module has an integrated high voltage detection circuit and a 45s switch on delay whereafter the output tube current gently increases, after the heaters or filaments have had their chance to heat the cathode. This avoids clicks and plops, and enhances tube life.
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code: TENT_BIAS
 APPLICATION and MOUNTING NOTES
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Electrical specification:
- Output voltage range to grids: -2Vdc to -85Vdc or -2Vdc to -160Vdc
- Output sink & source current: max 1.5mA
- Input mains voltage: 115Vac or 230Vac (+6% / -10%)
- Input range high voltage sense: 200V to 500V
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Mechanical specification:
- Total size 100*100*40mm (W*L*H, standoffs excluded), can be separated in 2 equally sized boards
- Hole pitch 91mm * 91mm (symmetrical)
- Total size separated boards 49*100*40mm (W*L*H, each board, standoffs excluded)
- Hole pitch separated boards 91mm * 40mm (symmetrical, each board)
- Hole size 3.5mm
- Weight 375 gram
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PRICE 1 off: £143.26 + vat + p&p
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