Weber BiasRite users, how the heck does this thing work?

[That90'sGuy]

I got in my BR-2 and I don't know how to use it. The directions on the website aren't very clear and I didn't receive any documention.

I know I'm supposed to let the amp warm up on standby, then turn on the amplifier and the BiasRite to get readings. What is the whole "A,B,C,D" thing on this? Anybody know what I should set my dual EL-34 Bogner Shiva to? 35ma or so?

Can anybody provide any insight into this because I'm lost???

 

[UfoPilot]

Re: Weber BiasRite users, how the heck does this thing work?

The A,B,c,d thing selects the tubes.did you get the one that reads the voltage? Mine has a switch that reads the plate voltage and cathode current. I take a voltage reading and flip the switch and take current reading and thenn multiply the two numbers. you might have to move the decimal point two places.

The power dissipation calculation is plate volts times cathode current.(Vp*Ik)

 

[Scott_F]

Re: Weber BiasRite users, how the heck does this thing work?

You really need to calculate the high voltage on the tube to accurately know what your bias settings should be. I just finished jeremy's latest amp.

Go to the Weber bulletin board and click on the tubes section. There is a bias calculator there where you can select your class, your tube type and then enter in your voltage. Works great.

Now, if you have more than one of those Weber adapters, you can plug them into a and b and then you can select back and forth between the tubes. I"m not sure that's too useful for me.

 

[Chaos]

Re: Weber BiasRite users, how the heck does this thing work?

The BiasRite has a selector switch labeled A, B, C and D. These selections are used to choose between tube sockets 1, 2, 3 or 4. If you only have one tube socket connected choose “A”. If you have two sockets connected you can toggle between them with ‘A’ and ‘B’. Three sockets….


To bias your amplifier:

First you need to know the maximum power dissipation (in watts) for the type of tubes you are using. Take 70% of that value. This is your target.
Then measure the plate voltage and plate current using your BiasRite and a multimeter.
Multiple the voltage x current to find watts. Adjust your tube bias to match your target.

You could also just adjust your bias current to a ‘recommended’ value, but that is just a guess that may or may not be appropriate for your amp.

 

[That90'sGuy]

Re: Weber BiasRite users, how the heck does this thing work?

Aha, that all makes sense... thanks guys!

I was initially confused by seeing 4 different switch positions on a 2 tube meter. I didn't realize 2 of them weren't active, it's just A and B to switch between the two power tube slots. I guess it was cheaper for Weber to keep uniformity with parts rather than ordering separate parts for different models.

This'll be my first time biasing an amp, so I'm a little slow to this stuff :smack: I need to try and find the bias pot for the Shiva next... :chairfall

 

[That90'sGuy]

Re: Weber BiasRite users, how the heck does this thing work?

Oh yeah, since you're supposed to adjust for each individual power tube rather than an average for the two (from the way it looks on the BiasRite), are there two bias pots to be able to set each one individually?

 

[Scott_F]

Re: Weber BiasRite users, how the heck does this thing work?

Oh yeah, since you're supposed to adjust for each individual power tube rather than an average for the two (from the way it looks on the BiasRite), are there two bias pots to be able to set each one individually?

On most amps, there is only one bias pot. The old silverfaced fenders ahve a bias "balance" pot where your dual headed adapter would be most useful.

 

[That90'sGuy]

Re: Weber BiasRite users, how the heck does this thing work?

On most amps, there is only one bias pot. The old silverfaced fenders ahve a bias "balance" pot where your dual headed adapter would be most useful.

Thanks for the reply and insight Scott, it was very helpful

I guess I overbought :smack: Hmmm... then the 4 tube switcher must really be a waste :27: Nice, now atleast I know what to look for on the inside of my amp :laugh2: Ok, looks like I'll be checking power dissipation first from the BiasRite, calculating it online and biasing the amp accordingly tomorrow.

Wish me luck! :fingersx:

 

[Gearjoneser]

Re: Weber BiasRite users, how the heck does this thing work?

I usually like to set books under the transformers, when the chassis is flipped over and plugged into the cab. Make sure you use gloves or a plastic handled mini-screwdriver when turning the pot, so you don't electricute yourself.
If the numbers on the bias rite start jumping around and don't settle, turn off the amp, let it cool for half an hour, and start again. Sometimes, when turning the pot, you'll get the tubes hot and the numbers won't settle.

 

[That90'sGuy]

Re: Weber BiasRite users, how the heck does this thing work?

Ok, first step done... checked the plate dissapation and it's 474V, the calculator says 36.9 ma should be about right (according to the Weber chart, it seems like that's the "hot" end of the bias. Maybe 35ma isn't a bad setting considering 32ma is considered "average".

How long should I keep the amp on standby before adjusting? Last time I checked, one EL-34 tube was at 16ma and the other was at 17ma and it looked like they were slowly climbing. Is this normal? Should I be adding the ma from each tube to get the numbers like 30-40ma? (And WHY doesn't it explain any of this on the website???????? Either way, I'm not getting 30ma on either one of the tubes right now like what is shown in the diagram on the website and I'm not sure what's going on with this thing).

Please, anyone?

 

[That90'sGuy]

Re: Weber BiasRite users, how the heck does this thing work?

Can anybody give any feedback on this?

 

[Scott_F]

Re: Weber BiasRite users, how the heck does this thing work?

You shouldn't have to be adding them together.

Some tubes are just different. I was biasing different tubes in jeremy's new amp today. I'd put in the Tung Sol 5881's and bias them to 41. Then I'd put in the TAD's and the bias current was 34, so I had to bump them up to 41. THen I put in some Winged C 6L6's and the bias was 32 or so.

So, new tubes could clock in at 17 when they should be a lot higher.

Just let hte amp warm up for 30 seconds or so. Then take it off standby and when the numbers settle, the tubes are ready to be biased. It shouldn't take very long.

 

[mrid]

Re: Weber BiasRite users, how the heck does this thing work?

This helps me: http://www.webervst.com/tubes/calcbias.htm

IIRC, and it's been a while since I retubed/rebiased my Shiva so my memory might be a bit rusty, the plate voltage is around ~500VDC. I believe I set mine somewhere between 34-36mA. Anyway, I'd err on the lower side of that 30-40mA generally accepted range because of this.

That's a good thing that the tubes are biasing so low, at least I think so, for the Shiva. I remember getting a set of Winged C's that would not bias under 45 or so mV. I think this is what Scott's getting at...tube draw? The numbers you are seeing will most likely be a bit off, but not too much, as they are likely matched within a given tolerance range.

As for increasing the bias, have you adjusted the pot as far as it will go and still get around 17mA per side?

 

[That90'sGuy]

Re: Weber BiasRite users, how the heck does this thing work?

Hmm... I just don't get why each tube is only putting out around 16-20mA... will this change over time??? I feel weird just leaving tubes at that, but it sounds good right now, so maybe I should give it a week and check again?

Yep, I'm with you mrid, my plate voltage was around 475, so it's not too far off. I guess I'll have to check back with this, but so far I don't like the readings I'm getting (maybe I have a bad meter, although it read plate voltage just fine....???) Glad to see you're back mrid

 

[Scott_F]

Re: Weber BiasRite users, how the heck does this thing work?

His question still holds though, *can* you bias it to the right spot (34?) or do you have the bias pot maxed out in that direction?

If so, you might require a new resistor in that bias circuit.

Email Bogner if your'e in this situation.

 

[That90'sGuy]

Re: Weber BiasRite users, how the heck does this thing work?

His question still holds though, *can* you bias it to the right spot (34?) or do you have the bias pot maxed out in that direction?

If so, you might require a new resistor in that bias circuit.

Email Bogner if your'e in this situation.

Unfortunately, I can only bias it to 27mA when the pot is maxed out. Looks like I'll be shooting Bogner an e-mail. Thanks for your help Scott!

 

[Gearjoneser]

Re: Weber BiasRite users, how the heck does this thing work?

I've asked Bogner before, and they say 35mA, although I think mine is around 36-37.

 

[That90'sGuy]

Re: Weber BiasRite users, how the heck does this thing work?

Alright, good update! I called up Bogner and got the rundown on where the bias resistor is and all I have to do is put in a slightly lower value (it's resistor R53 and I need to take out the 68k and put in a 50k).

I also learned something valuable today, always bias while playing your amp because it changes the readings a lot. Playing, looking at the bias meter, with the pot fully cranked, I got up to 36ma playing heavy chords (27ma when I just took it off standby, no playing), so maxed out, it's just about perfect.

Reinhold was a great guy, very down to earth and extremely helpful. Big props to that guy for explaining it all to me :fing2:

The sound is so much better now that it's biased a lot hotter. The overdrive is more aggressive and has more harmonics, the cleans are warmer and fatter and since I have new tubes, the bass stays together. Overall, I'm really happy with the end result