Bias Tool

  • Thread starter Thread starter shampoch
  • Start date Start date
i use the one from ted weber. $110 include meter and duet bias probes. push one button for current and another for plate voltage.

steve
 
i.ak":9w4qzsdi said:
I use a more or less basic multimeter or TAD BiasMaster (see link bellow).

http://www.tubeampdoctor.com/index.php?cPath=74
Click to expand...

Hey i.ak (or anyone else), l am thinking of getting that TAD BiasMaster soon to be able to bias both my VH4 and my ENGL Savage whenever I need new power tubes. Would you know, do I need the multimeter with two probes or the one with four probes? At the moment I think I'd need two probes only, to be able to bias each side at a time (i.e. 2x2 tubes), but I'm not sure as there are 4 tubes in total with the VH4 (as you might be able to tell from this I don't know too much about these things)... thanks!

cheers

jjj
 
there is only one bias adjustment pot on the VH4. not sure about your engl. i use the weber with 2 probes for shits and giggles. buy a matched quad of tubes and you will be set.

steve
 
jjj123":dum4u7jf said:
i.ak":dum4u7jf said:
I use a more or less basic multimeter or TAD BiasMaster (see link bellow).

http://www.tubeampdoctor.com/index.php?cPath=74
Click to expand...

Hey i.ak (or anyone else), l am thinking of getting that TAD BiasMaster soon to be able to bias both my VH4 and my ENGL Savage whenever I need new power tubes. Would you know, do I need the multimeter with two probes or the one with four probes? At the moment I think I'd need two probes only, to be able to bias each side at a time (i.e. 2x2 tubes), but I'm not sure as there are 4 tubes in total with the VH4 (as you might be able to tell from this I don't know too much about these things)... thanks!

cheers

jjj
Click to expand...


Two probes are fine, but with four it's easier and faster. This is because then you do not need to remove the tubes and change the probes when you want to check the other two tubes' bias. You know, before removing the tubes you need to turn of the amp and I think that the cost for additional two probes is not that significantly higher.

There is only one bias adjustment pot in VH4 (as in ENGL as well).

If you do not know much about these things I strongly recommend getting a bias tool rather than starting to experiment with the wires and multimeter. You can kill yourself (or your amp) if you do not know what you are messing with inside the amp.
 
i.ak":31dy46uk said:
If you do not know much about these things I strongly recommend getting a bias tool rather than starting to experiment with the wires and multimeter. You can kill yourself (or your amp) if you do not know what you are messing with inside the amp.
Click to expand...

Yep, that was my line of reasoning... I don't wanna kill myself and these things seem to make biasing possible without too much risk! Guys, thanks very much for your answers so far!

One more question though - let's say I'd get one of these Bias Tools (with 4 probes). Now the VH4 has one bias pot and I should bias only two tubes at a time. Can I bias both pairs with the same pot? How does that work? Maybe this is a stupid question but I don't really understand this!

Thanks again!

By the way, sorry for "hijacking" this thread but I thought It'd fit in here quite well...

Cheers

Jan
 
Having been on the receiving end of a transformer shock, I can attest that using a bias tool is a much safer way to do it! I use the Weber and like it. I had to nag them a few times to get my order shipped (took about 6 weeks total), but it's a nice tool to have.
 
i can't get a email response from them and that's with - "I want to place an order" in the subject line! :doh:
 
jjj123":2g06zm0w said:
i.ak":2g06zm0w said:
If you do not know much about these things I strongly recommend getting a bias tool rather than starting to experiment with the wires and multimeter. You can kill yourself (or your amp) if you do not know what you are messing with inside the amp.
Click to expand...

Yep, that was my line of reasoning... I don't wanna kill myself and these things seem to make biasing possible without too much risk! Guys, thanks very much for your answers so far!

One more question though - let's say I'd get one of these Bias Tools (with 4 probes). Now the VH4 has one bias pot and I should bias only two tubes at a time. Can I bias both pairs with the same pot? How does that work? Maybe this is a stupid question but I don't really understand this!

Thanks again!

By the way, sorry for "hijacking" this thread but I thought It'd fit in here quite well...

Cheers

Jan
Click to expand...


There is no stupid questions - only unknown surprising answers. ;)

The bias adjustment pot affects all four tubes. Thus, in a way you do not need to know all four tubes bias individually, but very often even so called "matched" pairs or quartets or sextets or octomillionets may have at least some variety. The thing here is that, you may want to make the two pairs' bias as even as possible (two "inner" tubes vs. two "outter" tubes). Also, by checking all four tubes' bias you will immediately recognize if a tube is bad or out of bias range.
 
i just order matched quads and check 2 pots as that is what my bias rite has. it costs no more for a matched quad than 2 matched pairs. with the VH4, if i am going to the trouble of removing the chassis, i will change all 4 and be done with it. if you got one with four probes, you would be seeing just how close your quad is matched. with the weber, you will read the bias for one pot (i.e. 32 ma or whatever comes up), not combined for the pair or quad. so no bar napkin math to determine each pot bias. i ran my bias up to about a 36 for the first tube. the rest fell in line from 34-36. flip the switch on the weber, and you can ready plate voltage, which is about 480 for the VH4.

steve
 
Everyone, especially Steve and i.ak, thanks so much for your help - and sorry for my late reply! I think I might be starting to understand how this stuff works (or at least how I could bias my amps)...

So as I understand it: in case of the VH4, I'd basically buy 4 matched power tubes (EL34 in my case), take the head out of the headshell, put in the four new tubes with the four probes between tubes and amp, turn the amp on (connected to speakers of course) and read whatever the bias-tool tells me.

I would do this for the first tube (as I believe that I can only "read" one tube at a time) and adjust the bias pot accordingly in order to bias the first tube "right". Then I would check the values for the next tubes, which should be somewhere in the same ballpark (+- a few ma). When they are all really close to what I'm aiming at I don't have to do anything else.

If they were showing somewhat different values, I'd go about finding some "middle ground" - i.e. if the first tube was at 35 and one other tube at 39 (and the others in between) I'd know there is a difference of four ma between the most "extreme" tubes. Then I'd try to adjust the bias so as to have all tubes around my "target value", knowing I can only adjust the overall bias and not a bias "per tube". So if i was aiming at 35 I'd have to lower the bias somewhat so that the tubes would be between say 33 and 37. I hope this is correct?

Guys, sorry for the long text but I didn't wanna bother you with 10 more questions so I wrote this up so that all I need from you now is a "yes you're absolutely right" or a "nooooo - you're gonna kill yourself and the amp too" ;)

And one more question; with the TAD Biasmeter, you can only read "ma" and not the plate voltage which steve mentioned. Is that a reason to look for another bias tool or do I not necessarily need to know the plate voltage?

Thank you all very much again and sorry for the long post!

Cheers

J

(PS: I know that there's quite a lot of info available online about biasing but i think it's pretty hard to understand and sometimes mixed up so I hope to find some answers here! thx)
 
Correct! :thumbsup:

It is not absolutely necessary to check all the tubes (as Steve stated), but that is what I want to do always. The matched sets are not that matched always. Remember that the tubes are pairs (outer two and inner two) so take that into account when swapping them around. Also, that is extremely easy way to diagnose a bad tube, which can be malfunctioning due to transportation mishaps etc. Makes it easier to claim for new tubes from the dealer :gethim: .

And no, you cannot read the plate voltage with the TAD, but it should be 480 V (DC) for VH4. You can check that from the withins of your amp by a multimeter capable of reading current of that range, but if you get propper bias readings for the tubes and it sounds good there is no need for checking the plate voltage.

I know what will be your next question: "How can I know what is the suitable bias range for my particular tubes?" ;)
 
i.ak":3tc9e8yh said:
Correct! :thumbsup:

It is not absolutely necessary to check all the tubes (as Steve stated), but that is what I want to do always. The matched sets are not that matched always. Remember that the tubes are pairs (outer two and inner two) so take that into account when swapping them around. Also, that is extremely easy way to diagnose a bad tube, which can be malfunctioning due to transportation mishaps etc. Makes it easier to claim for new tubes from the dealer :gethim: .

And no, you cannot read the plate voltage with the TAD, but it should be 480 V (DC) for VH4. You can check that from the withins of your amp by a multimeter capable of reading current of that range, but if you get propper bias readings for the tubes and it sounds good there is no need for checking the plate voltage.
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Man, thanks again! You rock!

But what do you mean with "swapping them around"?


i.ak":3tc9e8yh said:
I know what will be your next question: "How can I know what is the suitable bias range for my particular tubes?" ;)
Click to expand...

Nope! :D I think I kinda know that now because Duesentrieb posted something about this (at least for the VH4) a while ago... plus I found some stuff online on how to figure this out (although I haven't had the time yet to really look at that properly).

But anyway, if you want to explain I'm not gonna say no ;-)

No, seriously, thanks so much for your help!

J
 
i.ak":15vixcuz said:
By swapping I ment, that changing the places of new tubes if you want to make the pairs more even. However, the variation should not be too much.

For the suitable bias range you might find the links bellow rather interesting:
http://www.webervst.com/tubes1/calcbias.htm
viewtopic.php?f=14&t=32936&hilit=+plate+voltage+

And yes, please DO trust Duesentrieb and follow his instructions.
Click to expand...

Thanks, I guess I can call you my personal biasing consultant by now! ;)

Yep, the second link is the one I meant with Duesentrieb's info... the other one is really good too! Very helpful!

Ok so I think I'm ready to go now... thanks again!

J
 
No problem on the assistance.

The last tubes I bought were SED Winged C 34's from the Tube Store (http://www.thetubestore.com) and a set of Chinese 12AX7's with a Tung Sol in the V1 position and a balanced Chinese in V7. If you order online, buy 2 matched sets of power tubes and put in the comments you want it a matched quad. All were measured at 45 and he puts a little sticky on them to show you. I did check all 4 when I put them in just to see, as this is the first time I had bought tubes there. Yes, the bias was pretty even across the 4 of them.

If you go to Weber's site, he also has a bias calculator on there and ranges for tube families as were to set the bias. Plug in plate voltage (480 for the VH4) and you can also check it with the Weber tool. The calculator will spit out the bias with 70% dissipation built in. I set mine at 36 mA.

One thing Randall did well with at Mesa, self-biasing! Noodling around with this $4500 amp is half the fun though.

Steve
 
Steve, thanks again for the great info! You guys rock!

It'll be a few weeks until I'll get that bias tool but I'll let you know how it went...

Cheers

Jan
 
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