Dougs Bias Tester / Cant Find Order Page

[plexi50]

Maybe i need some visiene but i cant find an order page for Dougs bias tester kit
The one with the PC board that i need to assemble*

[John]

http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Tools&ORDER_ID=!ORDERID!

I think that's it.

EDIT... fixed link... sluckey

[plexi50]

Thanks i just found them. In the tool page. Order placed. I built one a few years ago and forgot to put the 1 ohm resistor on pin 8. I had filled the socket with JB Weld. It was too late to go back in the socket. I have some dummy days

[sluckey]

Doug's bias checker doesn't have a 1Ω resistor, but you can add one internally or just put it across the dual banana plug screw terminals.

[plexi50]

Thanks Steve. My friend has a Compu Bias. I love that tester. Maybe i will buy one with money from the next amp i sell

[EL34]

As Steve said, there is no one ohm resistor

The bias Checker routes the cathode current through your multi meter
You set your meter to DC milliamps and read the current flow.

The assembly instructions link for the bias checker is right next to the order button on the tools page

[plexi50]

Like this? Super fast delivery* 1r 3 watt across terminals

You can move this to the amp tools section. Thanks all!

[Willabe]

Hey Plexi, That looks nice.

I think I'm gonna have to get me a pair of those.


               Thanks,   Brad    

[plexi50]

It's a must have anyway you look at it. I built a few a couple years ago and at some point i needed the shielded cable i used to make them. The tube amp builds come first if you know what i mean. I am going to buy 3 more from Doug as soon as i pay next months bills again. Dam never ending cycle of slavery. Slavery is alive and well /

[LooseChange]

I have a couple. I need to build a box to accept 2 or four of these so I can switch between tubes when biasing.

[plexi50]

Out of all the tools we need, i have no clue as to why i have not bought the bias probes up till now other than to say i am always concerned about the next electric bill. I could buy and plug in a 7'x7' Spa though

[Jack1962]

Ok I hate to sound stupid , but here we go , if there needs to be a 1 ohm resistor in line with the cathode , why isn't it included in the kit? 

[stingray_65]

Ok I hate to sound stupid , but here we go , if there needs to be a 1 ohm resistor in line with the cathode , why isn't it included in the kit? 

It's like this:

If you put the 1 ohm resistor in it you read on your mV scale of your meter. mV will = mA. What you are reading is the voltage drop across the resistor.

If you do not use the 1 ohm resistor you must use the mA scale on your meter.

Most meters read both mA and mV so its a matter of preference

Ray

[Jack1962]

Yeah that's what I was think 

[sluckey]

Here's a good reason to put 1Ω resistors across the banana plug...

http://www.el34world.com/Forum/index.php?topic=12987.0

I don't have any bias testers, but if I did, I'd have a pair or maybe even a quad. And there would be a 1Ω resistor on every bias tester. Using a single tester to check bias in a P/P amp seems very inefficient to me. You gotta plug it in, check the current, power down, plug into another socket, power up, and check the other tube current. Maybe you need to make an adjustment. If so, now you're gonna repeat that whole scenario.

I'd rather use two checkers plugged in at the same time. But wait, I've only got one meter, so I have to plug a tester into the meter, take a reading, then plug the other tester into the meter and take another reading. About the same effort as moving a meter probe from one cathode to another. But while checking one tube what do you do with the dangling, unused tester? If you are using Doug's tester as built, you'll need to short the unused banana plugs together to provide a ground for the tube that's not being checked. And that's the main reason I would put the 1Ω resistors on the banana plugs.

I don't personally have anything against checking actual current rather than volts across a 1Ω resistor. But I've seen many, many casual amp tinkerers that barely know how to use their meter. Checking current means turning a function switch and may even mean moving meter leads to another meter hole. This can lead to some confusion, and possible damage to the meter if you forget to change the function switch AND meter holes when you go to check plate voltage. Using the 1Ω resistors can simplify the bias test and may even save your meter. I'm not picking on tinkerers. Accidents happen to everyone. I've blown an expensive meter before!   

[Jack1962]

Yes I understand what you saying , I just wasn't thinking of measuring voltage , and yes I too have seen many tinkerers blow meter and alot more up . I agree checking bias one tube at a time that way would be a real pain . I would be something fun to build during break though.

[plexi50]

Well if anyone comes up with a switching method im game to build one

[PRR]

> Checking current means turning a function switch and may even mean moving meter leads to another meter hole. This can lead to some confusion, and possible damage to the meter

The Amps function on my Fluke takes a VERY EXPENSIVE fuse. (How would I know that?)

[EL34]

Ok I hate to sound stupid , but here we go , if there needs to be a 1 ohm resistor in line with the cathode , why isn't it included in the kit

I already explained this
read reply #5

You don't use a 1 ohm resistor, you read the current flowing through your meter

If you want to use a ohm ohm resistor, just install them on your power tube sockets and use the bias probe jacks that I sell.

If you want to alter the bias probes, that your business


 

[Fresh_Start]

I prefer to read the actual current rather than wonder about the accuracy of a 1 ohm resistor and how well my meter reads millivolts.

At first I had only 1 bias probe.  Frustrating, so I built a second with an extra tap to measure voltage between the plate and the cathode.  I also got a female bannana plug and shorted across the terminals inside so that I can safely jumper the unused bias checker.  Do I have to be really[/i]careful with this setup?  YES  And it takes two meters, but it speeds up the process and gives me good results.  Especially helpful when trying to dial in an amp with bias vary tremolo.

Cheers,

Chip

HINT to Doug - female bannana plug connector.

[sluckey]

HINT to Doug - female bannana plug connector

Most banana plugs are hermaphrodite. I've got 6 stacked up right under my monitor.   

Ever think about putting the banana plug in series with pin 3? No more wondering how much of that cathode current is actually flowing thru the plate. Be careful.

[EL34]

HINT to Doug - female bannana plug connector

As Steve pointed out
You can plug one banana plug into the back of another one

They are male on one end and female on the other

[Jack1962]

hell I still think it would be a good break time project , and I am going to buy the materials to build it from ya doug 

[TubeGeek]

> Checking current means turning a function switch and may even mean moving meter leads to another meter hole. This can lead to some confusion, and possible damage to the meter

The Amps function on my Fluke takes a VERY EXPENSIVE fuse. (How would I know that?)

  I learned the same lesson when I built my bias testers.

[EL34]

My radio shack meters take a .10 fuse

The only way I blow a fuse is if I forget and leave the meter on Resitance/continuity and then check a voltage

After blowing up a couple expensive meters in my shop back in Sarasota, I only bought radio shack meters for my bench
Have had the same RS meter for 10+ years and it's still going good.

When you are measuring cathode current on a power tube you are measuring less than 50 milliamps and there is no high voltage like the plate shunt method

Not sure if some people understand how the whole deal works?
Sounds like a few are scared to set their meters to DC milliamps?

[Jack1962]

I have no fear of testing current , I have tested systems with over 10,000 amps of current, so a unit that the max current is 7 amps doesn't scare me at all. I fully understand how to use test equipment , I was a electrician for 20 years and have been a technician for about the same . I do understand how your bais probe works , I think it is a fine addition to any test bench.

                                                            Jack Latham
                                                  Latham Electronic Systems

[plexi50]

Hey Plexi, That looks nice.

I think I'm gonna have to get me a pair of those.


               Thanks,   Brad    

Yeah it went together fairly easily. I am going to order one more next week. Best to have a pair of them at least.

[EL34]

I have no fear of testing current , I have tested systems with over 10,000 amps of current, so a unit that the max current is 7 amps doesn't scare me at all. I fully understand how to use test equipment , I was a electrician for 20 years and have been a technician for about the same . I do understand how your bais probe works , I think it is a fine addition to any test bench.

I wasn't speaking to anyone in particular
I just got the impression several people really did not understand that a meter can measure DC miliamps current flow because they are adding one ohm resistors to my bias probe.
Just in case someone else reads this, you are measuring less than 50 DC milliamps, no where near 7 amps (7000 milliamps)

[plexi50]

I think i got confused about the 1ohm resistor myself weather i needed it or not. I understand now that it is not needed. I was also reflecting back on an Ebay sellers bias testers,claiming that most other sellers did not have a 1r resistor and that theres did making there bias probes safer or better.  Heres another question: Why dont all amp manufactures put that 1r on the cathodes? I see many schematics using mv info instead of ma info. Why is that? 

[EL34]

Why dont all amp manufactures put that 1 ohm on the cathodes?
I see many schematics using mv info instead of ma info. Why is that?  

I don't know
The 1 ohms are on all the amps I built

If you have an external bias pot, use these test probe jacks
I sell tons of these, so lots of people are using them
You use one black and two reds in a two power tube amp

You can even install them on cathode biased power tubes to check the voltage drop across your cathode resistor

[plexi50]

I believe i bought some from you a year or so ago. I liked them because they were smaller than what i was getting at Radio Shack.  They take up very little rear panel space unlike the bigger test probe jacks