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Pictured: Noval
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Bias Master™ - TAD, tube tester, with 4 probes
Bias Master™ system BM4 Measures Bias current of the vacuum tubes in your amp. Includes 4 probes and english/german operation manual.
The Bias Master™ allows you to monitor the bias current safely and easily. While adjusting the Bias control pot of your amp, the Bias Master™ shows the actual result. This lets you set and evaluate the full reasonable biasing range your amp and tubes offer to find and set your personal perfect choice.
The Bias setting has a dramatic impact on the amp's response, break-up and dynamic character.
| Probe Type | Measures |
|---|---|
| Octal | 6L6GC, 6550, EL34, 6V6GT, 5881, KT66, KT88, KT90, KT100, KT120, 7027A |
| Noval | EL84 types |
For additional probes (for testing other types of tubes), see S-TBMA2-X
Accessory Items:
| Probe Type | Our Part Number | UPC/EAN |
|---|---|---|
| Octal | S-TBM4 | 841358106163 |
| Noval | S-TBM4-EL84 | 841358106170 |
| Item Height | 2.1 in. | |
| Item Length | 5.76 in. | |
| Item Width | 3.6 in. |
| Packaging Dimensions | 8 in. × 5 in. × 3.75 in. | ||
| Weight (Packaging) | Noval version | S-TBM4-EL84 | 0.922 lbs. |
| Octal version | S-TBM4 | 1.048 lbs. |
| S-TBM4 - Octal version | Item Height | 2.1 in. |
| Item Length | 5.76 in. | |
| Item Width | 3.6 in. | |
| S-TBM4-EL84 - Noval version | Item Height | 2.1 in. |
| Item Length | 5.76 in. | |
| Item Width | 3.6 in. |
 Operation Manual | All Models |
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Specifications, Files, and Documents
Questions and Answers
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3 answers
Does it come with a list of different amps to get bias numbers from ?
Asked by Anonymous on January 15th, 2019.
January 16th, 2019
Staff Member
No, such a list is not included with this meter, but we have provided a bias calculator that may be of assistance: https://www.amplifiedparts.com/tech-corner/tube-amplifier-bias-calculator
I was looking at the formula to calculate bias. It's states "Let’s say we found it (PLATE VOLTAGE) measured 420VDC..." How does one measure that ? Does the Bias Master have that capability ? I notice for the 6L6GT in the equation 420V is used but that value differs a lot from both what is on the pdf file and the sheet that shown on the video of 300 -390 V for that tube.
If you know your plate voltage, you calculate bias current by multiplying the percentage of max wattage you want, typically 70%-80%, and divine that result by the plate current. For example, if your plate voltage is 408 VDC, 75% of 19 watts max (this is for 7591A tubes) is 14.25 watts, divided by plate voltage = .035 amps or 35mA. Set your bias current at 35mA.
1 answers
Can you bias an amp with a multimeter?
Asked by Anonymous on November 8th, 2017.
Yes you can but the bias meter simplifies the process and does the mathematical conversions for you.
1 answers
I received the bias master. However, I am surprised that the manual and inside did not mention that it can measure KT120 tubes unlike it is mentioned in your website. Please confirm that it can be used on KT120 or not.
Asked by Anonymous on April 12th, 2018.
According to the TAD site this measures KT120 tubes. You may want to contact them for confirmation.
1 answers
I read the bias calculations and understand how in your example to get 70% of I (bias voltage). In equation I = P/V. I see that value for P of 14W is listed for the 6V6GT right on your .pdf file that will also be included if I purchase the Bias Master. However, you stated you measured V, the plate voltage (420V) in your example. (as opposed to using measurement chart shows V to be 300 - 390, so it seems measurement prevails) How would I find that value out myself without any additional equipment ? Also say in 100W Marshall P is listed as 25W but for EL34's, but If my Marshal 100W amp is using 6550's can I use the P value for Ampeg SVT since that amp lists 6550A as that tube type ?
Asked by Anonymous on January 23rd, 2020.
January 23rd, 2020
Staff Member
A multimeter would be required to measure voltage. For questions on how to properly bias your specific amplifier, we advise consulting a professional repair tech.
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