TAD Bias Master BM4

Measuring Device For Bias

  • Four octal socket adapters
  • For the control of the retirement
  • At 6L6GC, 6550, EL34, 6V6 GT, 5881, KT88, KT66, KT90, KT100, 7027A
  • With illuminated display
  • Made in Germany

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TAD Bias Master BM4
Robert814, 09.03.2014
This model comes with 4 octal probes, but I ordered 2 noval probes as well so that I can set up EL84's as well as 6V6's and 6L6's etc.
WARNING! - There are no instructions! - If you don't know what you are doing, don't try to use this unless you have a friendly tech to show you. You can download them from the TAD site, 2 sides of A4 folded into a leaflet. Very basic instructions.
The probes each contain a 1 ohm resistor in the cathode lead, so they are measuring total cathode current (anode + screen grid). Circuit schematic diagrams usually state a bias Voltage (e.g. -37Volts) rather than current. This is a good starting point, but then you need to find the valve manufacturer's specifications from their data sheets. Then you can balance up each side of the push-pull stage.
The readout on the unit is 00.0 mA to presumably 99.9 mA.
A "Chicken head" pointer knob selects each of the 4 individual valves, or the OFF position.
It's really simple and easy to use (as another reviewer has said) and you don't have any high voltage connections to make through a test meter. The real skill is knowing just where to set the current level, which is of course different for each and every valve type and can be slightly tweaked for your preferred sound.
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quality
It`s okay
Amateur Slash, 27.05.2017
Unfortunatelly there aren?t too many options on the markt to choose from.
Would have preferred a tool that can measure the plate voltage too.
It does though what it says in it?s title therefore i?m quiet satisfied with this product.
Quality of the material has a bit of a cheap expression.
Color coding or numbering would have been preferable for the cables.
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Decided not to keep it.
Ian294, 15.02.2015
I bought this as an upgrade to my previous method of basing my amps which consisted of a multimeter and simple bias probe.
However I found that the BBM4 unit gave widely differing readings so I decided to revert to my old simple method of biaising and sold the Bias Master.
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Very handy
Tore Stjerna, 14.08.2014
This is a great thing to have around if you use tube amps. Gives a clear mA readout of each tube. The probes are in pairs and have white and red RCA connectors in the other end. I only wish that they had marked the probes so you would know which is which. I've done this myself of course, but I think it should have been like that out of the box.
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£129
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