Compu-Bias Automaic Bias Meter Fully Automatic Tube Amp Bias Meter

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Quick FAQ Page

Q-Does the Compu-Bias use filament voltage?
A-No, the filament voltage is not used by the Compu-Bias. Filaments are isolated from the measuring circuits.
Q-How does the Compu-Bias show balance?
A-Because the display is dynamic you can monitor Plate voltage and Cathode current for up to two tubes. Setting the bias balance to an equal dissipation value for both tubes will assure that the tubes are in balance. This is an important feature, it has been found that not all output transformer have identical resistance on both sides.
Q-Can the Compu-Bias be used with tubes other than the tubes listed?
A-Yes, please email us with specific requests or use the Contact Page.
The Compu-Bias will not work with directly heated Cathodes using a standard probe. Email for more information
Q-It seems to me that the Compu-Bias is pretty expensive. Why?
A-The Compu-Bias is an exceptional value and can actually be less expensive than some of the "others" if you add up the all the stuff you need to do the same job. It is purpose built for automatically calculating tube dissipation as an aid in the measuring and setting bias and balance. It is not a simple off the shelf meter /display with switches here and there that do no more than display a single value leaving you to do the calculations or figure out what you have measured. It is manufactured in the USA with as many US parts as possible. It is "soft" and can be updated as new features are released.
Q-Is there an advantage to using the Compu-Bias instead of the simple current only probe?
A-Yes, Current is only half the answer. You need to know the Plate voltage to figure the dissipation of the tube. For example, if you have a single 6L6GC tube with 320v on the plate @ 25ma the Plate dissipation would be 8watts. If there was 500v on the Plate @ 25ma the Plate dissipation would be 12.5watts. As you can see a simple current measurement is pretty useless without knowing the voltage. How you actually measure these values is another matter.
Q-I noticed that the Compu-Bias measures Cathode current. My buddy told me that this is incorrect. What about screen current?
A-Yes and No, The Compu-Bias (like most others) does measure Cathode current. This represents both Plate and Screen current. The Screen current should be no more than 10% of the overall Cathode current at idle (no signal) and in most cases much less than that. This actually adds a small safety factor to the dissipation results.
Q-I have seen many other products like this come and go how can I trust that you will be around until the warranty expires?
A- The Compu-Bias meter concept began development in 2005. The prototypes were built at the beginning of 2006. The production process started in the second quarter of 2006. After completing development of electronics, enclosures and software the unit was offered for sale in the last quarter of 2006. Since that date we have sold many of the devices with various configurations of probes. Comments from customers have been nothing less than amazing. As far as the future, we believe that we have a solid product and a solid business plan. Nobody here has a crystal ball (or would know how to use it if we did) so predicting the future is impossible. We do however expect to be around for a long time, are currently developing new devices and supporting our growing customer base.
Q-I can't see the value in the the Compu-Bias for a hobbyist. Why wouldn't any of the other methods be better for me? After all resistors are only 10 cents.
A- Everybody has their own concerns about value. Hobbyists and DIY types will find the Compu-Bias quite valuable. It only takes a single slip to damage an output transformer during voltage measurement or ruin a set of high dollar tubes because of improper bias. This can be far more expensive than the purchase price of any bias tool. In most cases it is also easier and safer for the amp than removing it from cabinet simply to check bias. 10 cent resistors are not typically 1% or better in tolerance and therefore not good enough to use as accurate shunts for measurements. Additionally these resistors would need to be installed on every Cathode pin of every tube in every amp you intended to check. You would then need to separately measure the voltage across each one of them and the Plate voltage for that tube then do the math. If you need to change the bias after the calculations are made for all of the tubes you need to start all over again.
Q-I have heard that this whole current measuring thing is a farce... you can't measure anything without affecting it, so you'll never know the current you're trying to measure, nor the voltage. Isn't this true?
A-Absolutely NOT, Even if you exclude the small voltage drop across shunt devices measurements can and are made daily expecting accurate results without affecting the circuit measured. Be it current or voltage, using meters, oscilloscopes, analyzers or whatever. This would be a concern if you need to permanently add various ancillary circuitry (like additional Cathode resistors) to the device to simply make those measurements, especially if they are not necessary for normal operation.
Q-Experienced ears can tell when bias is off. Playing the amp, you can set the bias just below the level that the Plates glow red. Some times there is not much difference then when checked with a meter, isn't this true?
A-NO, Experienced or not you can't hear proper bias. There is no way to tell if your tubes are being damaged by excessive currents simply by listening or looking for lack of red plates..
Q-I am not experienced with tubes or amps. What are the pins on your probes made from? Why aren't they gold?
A-Our probes are made from high quality sockets and bases. The pins in the bases are rolled and staked for years of service. We have hundreds of cycles on our test probes with no problems or failures. Gold or other precious materials are soft, this is why most connectors are only plated with these materials. Multiple uses may wear through the plating and actually create connection problems. Additionally very few if any power tubes found in either audio or guitar amplifiers were manufactured with gold pins.
Q-I found an error in the documentation or web-site and I am really excited about it, what should I do??? Would posting the error for comments in any forum I can find so my buddies can see it be the best way to handle this.
A-Actually NO , Questions, errors and comments can be emailed to or use the Contact Page. We appreciate your comments. Changes or corrections are reviewed and updates made as needed. Your buddies can't update or change the documentation or the web-site and probably have no idea how our products work or details of their specifications.

Compu-Bias reserves the right to change or cancel any information listed including availability, specifications, and technical information appearing on this site at any time without notice.
Compu-Bias Company
Lakewood, Colorado 80226

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