Alternative to rebiasing...

[Pierre]

Could I just take the plate voltage and send it to whoever would sell me the tubes and ask for a matched set..? Or I could do the method with taking the current across a 1ohm resistor between ground and pin 8 and read the tubes' voltage, but since they're very old I'm guessing it'd have decreased by now?

 

[MDS]

Re: Alternative to rebiasing...

What amp?

 

[Pierre]

Re: Alternative to rebiasing...

Laney AOR 30 combo. Two 6V6s power tubes.

 

[Lewguitar]

Re: Alternative to rebiasing...

You can't really do what you're saying. I adjust my bias by ear, BTW, and then measure it to make sure I'm in a safe range.

What you might want to do is buy a set of 4 or 6 matched tubes.

Install two and set the bias.

Then when they need replacing you could install the next set and you wouldn't have to readjust the bias.

Lew

 

[Quencho092]

Re: Alternative to rebiasing...

lew, when you bias, how do you listen for crossover distortion? And do you check it to make sure that it isnt over 70% so the tubes dont roast? Just curious, i've biased my amps with a bias rite, but i havent had a great result, I need some tips!

 

[Pierre]

Re: Alternative to rebiasing...

You can't really do what you're saying. I adjust my bias by ear, BTW, and then measure it to make sure I'm in a safe range.

What you might want to do is buy a set of 4 or 6 matched tubes.

Install two and set the bias.

Then when they need replacing you could install the next set and you wouldn't have to readjust the bias.

Lew

Yeah... My main problem IS setting the bias unfortunately. The only way to do it here would be to simply drop it off at the shop (a mile away, and I can't afford a cab), wait two weeks for it to be done, and pay 30 pounds (which I can't afford either..) so I'm screwed :jester: If I do end up doing this though I think I'll order 4 matched tubes, that's a nice tip thanks

 

[Lewguitar]

Re: Alternative to rebiasing...

lew, when you bias, how do you listen for crossover distortion? And do you check it to make sure that it isnt over 70% so the tubes dont roast? Just curious, i've biased my amps with a bias rite, but i havent had a great result, I need some tips!

Nope. I use the 1 ohm resistor method and set it by ear and then make sure it's not set to hot. My ear never lets me set it to cold. Lew

 

[wixedmords]

Re: Alternative to rebiasing...

Pott, the bias tools eliminate the need for the 1ohm resistor.

Now, I know what you said about a Weber being pricey, but there are bias tools on Ebay for much less.

If you can get plate voltage, you are half way there. Be careful of plate voltage though. Sometimes you can smell your filling melting.

I do understand if you want to do the whole process manually. Good luck.

 

[STRATDELUXER97]

Re: Alternative to rebiasing...

Pott, the bias tools eliminate the need for the 1ohm resistor.

Now, I know what you said about a Weber being pricey, but there are bias tools on Ebay for much less.

If you can get plate voltage, you are half way there. Be careful of plate voltage though. Sometimes you can smell your filling melting.

I do understand if you want to do the whole process manually. Good luck.

Those bias meters are nothing more than the 1 ohm cathode resistors and meters built right into a single unit...The 1 ohm cathode resistor method is what I've been doing for many years and it's cheap and easy to get the same results as those expensive meters....I Like to get inside of my amp when it's time to retube,but some guys install external banana plugs and a method of adjustment so they can bias without having to pull the chassis out..

 

[Pierre]

Re: Alternative to rebiasing...

The voltage reading... It's ground and pin 5 of power tube right..? So basically as I turn the bias meter I keep the voltmeter on and stop when I read the same measurement as the tubes? Of course I simplified it a lot haha I got this great website though:
http://www.duncanamps.com/technical/lvbias.html
If I understand correctly, those bias right tools don't save that much hassle if you're ok with soldering. They just allow you to do all the reading at once with the power tubes on and without having to do soldering...

Also, my amp doesn't have a bypass switch. When time comes to turn it on, should I just have all the controls down to 0?

 

[STRATDELUXER97]

Re: Alternative to rebiasing...

The voltage reading... It's ground and pin 5 of power tube right..? So basically as I turn the bias meter I keep the voltmeter on and stop when I read the same measurement as the tubes? Of course I simplified it a lot haha I got this great website though:
http://www.duncanamps.com/technical/lvbias.html
If I understand correctly, those bias right tools don't save that much hassle if you're ok with soldering. They just allow you to do all the reading at once with the power tubes on and without having to do soldering...

Also, my amp doesn't have a bypass switch. When time comes to turn it on, should I just have all the controls down to 0?

You're reading off the cathodes of the output tubes pins 1 and 8 are tied together on a Marshall and just pin 8 on Fender amps and these cathodes are grounded...The 1 ohm cathode resistor just changes milliamps to millivolts across the resistor....

Pin 5 gives you - bias voltage reading...We're talking about the 5881,6L6,EL34,6V6,and 6550 tubes specifically though..

 

[wixedmords]

Re: Alternative to rebiasing...

Those bias meters are nothing more than the 1 ohm cathode resistors and meters built right into a single unit...The 1 ohm cathode resistor method is what I've been doing for many years and it's cheap and easy to get the same results as those expensive meters....I Like to get inside of my amp when it's time to retube,but some guys install external banana plugs and a method of adjustment so they can bias without having to pull the chassis out..

Yes on the first part, most amps need the chassis pulled on the second part, to get to the bias pot, albeit many of the newer amps have outside test points.

On the first part, the bias tester is truely just a 1ohm adapter rig.

Either way is fine though. To each his own. It is cheaper and easier to do it manually.

But, one thing to think about here, the use of a bias tester, which is placed between the tube and the socket, minimizes the tech's time at the top of the tube socket where there are more opportunities to grab 300-500 volts.

The weber tester, while fairly expensive, even eliminates the need to get plate voltage at the top of the tube socket. It does it right at the bias tester.

Minimizing high voltage exposure is very important to me.

 

[STRATDELUXER97]

Re: Alternative to rebiasing...

Yes on the first part, most amps need the chassis pulled on the second part, to get to the bias pot, albeit many of the newer amps have outside test points.

On the first part, the bias tester is truely just a 1ohm adapter rig.

Either way is fine though. To each his own. It is cheaper and easier to do it manually.

But, one thing to think about here, the use of a bias tester, which is placed between the tube and the socket, minimizes the tech's time at the top of the tube socket where there are more opportunities to grab 300-500 volts.

The weber tester, while fairly expensive, even eliminates the need to get plate voltage at the top of the tube socket. It does it right at the bias tester.

Minimizing high voltage exposure is very important to me.

As always,a guy shouldn't be inside of an amp unless he knows what he is doing! The meter is safer for sure.I use the 1 ohm cathode resistors and know what I'm doing though. :13:

 

[Pierre]

Re: Alternative to rebiasing...

If I use rubber gloves am I safer? :jester:
It doesn't actually seem as hard as people make it to be. The main problem seems to be security if I get this right. I'll get tubes and maybe a better voltmeter once I have the money and give it a try. I think I'll try checking the bias on the old tubes first, then the new ones. If I'm not dead then And yes my tubes are 6V6s. So pin 8 for tube voltage and 5 for plate then.
Thanks guys! If you do have any other tips of course, feel free to tell...

 

[shredaholic]

Re: Alternative to rebiasing...

I use rubber gloves and wear slippers with rubber soles just in case! :laugh2:

The first few times you do it are quite nerve racking due to the high voltages you might tough, but you'll quickly get used to it and it'll be like second nature.

 

[Marcel]

Re: Alternative to rebiasing...

what rubber gloves? the red from an electronic store are f***in expensive?!

 

[Pierre]

Re: Alternative to rebiasing...

So basically, biasing is the process of balancing out plate voltage and tube voltage.

What are the risks if I work carefuly, slowly and I have a steady hand? I'm assuming that if there's no direct skin contact with the high voltage parts, it's safe? Would cloth take fire though?

 

[STRATDELUXER97]

Re: Alternative to rebiasing...

So basically, biasing is the process of balancing out plate voltage and tube voltage.

What are the risks if I work carefuly, slowly and I have a steady hand? I'm assuming that if there's no direct skin contact with the high voltage parts, it's safe? Would cloth take fire though?

You're scaring me reading this! :fingersx:

 

[Pierre]

Re: Alternative to rebiasing...

Why don't you just tell me John, or do you want me dead? :laugh2:

 

[STRATDELUXER97]

Re: Alternative to rebiasing...

Why don't you just tell me John, or do you want me dead? :laugh2:

I don't want you dead brother,but I'd rather you know you weren't going to hurt yourself by not being 100% sure of what you are doing....I'd not want to take any responsibilty in you hurting yourself....

I thought I already told you what to do? Do you need pictures on how to install 1 ohm cathode resistors across your output tubes,or are you using the bias meter?